61016529-PSV-anual

Safety and Relief Valve Testing andMaintenance Guide

Technical Report

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WARNING:Please read the Export Controland License Agreement on theback cover before removing theWrapping Material.

Effective December 6, 2006, this report has been made publicly available in accordance with Section 734.3(b)(3) and published in accordance with Section 734.7 of the U.S. Export Administration Regulations. As a result of this publication, this report is subject to only copyright protection and does not require any license agreement from EPRI. This notice supersedes the export control restrictions and any proprietary licensed material notices embedded in the document prior to publication.

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EPRI Powering Progress

EPRI TR-105872s Electric Power Research Institute August 1996

R E P O R T S U M M A R Y

INTEREST CATEGORIES

Nuclear Plant Operationsand Maintenance

Nuclear plant life extensionEngineering and Technical

SupportMaintenance support

KEYWORDS

MaintenanceRelief valvesValvesMaintainability

Safety and Relief Valve Testingand Maintenance GuideThis guide gives a broad overview of self actuated and power oper-ated pressure relief devices (PRDs) — safety, relief, safety relief, andpower-operated relief valves — and their application and mainte-nance. The non-reclosing devices, like the rupture discs, are outsidethe scope of this guide. The information in this guide, though directedtowards the nuclear power plant personnel, will assist all power plantpersonnel responsible for the maintenance of PRDs. This guide canalso be used by training instructors to develop course materials.

BACKGROUND In nuclear power plant applications, a high demand of reliabil-ity is placed on safety and relief valves. These valves might be required to openfor accident mitigation and reseat after system pressure is reduced and re-turned to normal operating conditions. Certain recent incidents involving im-proper operation of the relief valves in nuclear power plants have raised con-cern about their operability within the specified limits. This guide has beendeveloped to provide utility personnel with a background on valve design,selection, application, maintenance, repair, refurbishment, and testing to gain athorough understanding of the principles and operating mechanisms of PRDs.

OBJECTIVES

• To provide general information on PRDs

• To provide necessary guidance to power plant personnel responsible forselection, maintenance and testing of PRDs.

APPROACH EPRI organized a Technical Advisory Group (TAG) consisting ofPWR and BWR utility personnel, leading relief valve manufacturers and USNRCto provide input and review the guide. Plant visits were conducted and personnelfrom the manufacturers and various utilities were interviewed for detailed informa-tion. The Nuclear Plant Reliability Data System (NPRDS) and Licensee EventReport (LER) databases provided information on reported failures and theircauses by valve type. Highlights of ASME Code requirements for testing of safetyvalves along with guidelines on bench testing with auxiliary-lift devices are alsoincluded, as well as recommendations on predictive and preventive maintenance.

RESULTS This guide attempts to address the concerns of the operatingnuclear utilities as expressed in various documents (SERs & SOERs) issued bythe Institute of Nuclear Power Operations (INPO), and the USNRC in its reportAEOD/S92-02. This guide is divided in 10 sections that progress as informationbuilds from previous sections. Persons being introduced into the field of safetyand relief valves should approach this guide beginning to end. Experiencedtechnicians looking for specific information should refer to specific topicalsections. Appendices provide advanced information.

EPRI PERSPECTIVE During the period 1980–1982, EPRI and GeneralElectric conducted extensive research on pressurized water reactor andboiling water reactor safety and relief valves. Summary of this research ispublished in the EPRI report EPRI NP-4306SR. This NMAC document hasdrawn information from this report as well as other sources. This guide isdesigned to help utilities understand the root causes of any PRD problems,and mitigate them. Certain aspects of the PRD problems (for example,setpoint drift) are not well understood and are still being studied by themanufacturers and the various owners’ groups. These aspects have beenidentified and temporary remedies have been suggested. This guide canalso be effectively adapted for training of plant personnel.

PROJECT

Work Order 2814-82

EPRI Project Manager: Vic Varma

Nuclear Maintenance Applications Center

Nuclear Power Group

Contractor: QES, Inc.

For further information on EPRI research programs, call EPRI TechnicalInformation Specialists 415/855-2411.

Safety and Relief ValveTesting and Maintenance Guide

TR-105872

Work Order 2814-82Final Report, August 1996

Prepared byQES Inc.One Shell SquareNew Orleans, LA 70139

Edited byJ.R. (Dick) Zahorsky32 Quince Island RoadFranklin, MA 02038Engineering Consultant (Chief Engineer-Retired)Crosby Valve and Gage Company

Prepared forNuclear Maintenance Applications Center1300 Harris BoulevardCharlotte, North Carolina 28262

Operated byElectric Power Research Institute3412 Hillview AvenuePalo Alto, California 94304

EPRI Project ManagerV. Varma

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIESTHIS REPORT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORKSPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHEREPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW, NOR ANY PERSON ACTINGON BEHALF OF ANY OF THEM:

A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I) WITH RESPECTTO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THISREPORT, INCLUDING MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, OR (II) THAT SUCHUSE DOES NOT INFRINGE ON OR INTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY’SINTELLECTUAL PROPERTY, OR (III) THAT THIS REPORT IS SUITABLE TO ANY PARTICULAR USER’SCIRCUMSTANCE; OR

(B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER (INCLUDING ANYCONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVE HAS BEEN ADVISED OF THEPOSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOUR SELECTION OR USE OF THIS REPORT OR ANYINFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS REPORT.

ORGANIZATION(S) THAT PREPARED THIS REPORT

QES Inc.

ORDERING INFORMATIONPrice: $25,000.00

Requests for copies of this report should be directed to the Nuclear Power Maintenance Applications Center(NMAC), 1300 Harris Boulevard, Charlotte, NC 28262, 800/356-7448. There is no charge for reportsrequested by NMAC member utilities.

Electric Power Research Institute and EPRI are registered service marks of Electric Power Research Institute, Inc.Copyright © 1995 Electric Power Research Institute, Inc. All rights reserved.

iii

EPRI Licensed Material

Safety and Relief Valve Testing and Maintenance Guide

ACKNOWLEDGMENTS

The NMAC Safety and Relief Valve Guide was developed with the help of many orga-nizations and individuals. We specially wish to recognize the following individualswho volunteered to form the Technical Advisory Group and freely contributed theirtime and knowledge in molding this guide into its present form.

Robert Wright Crosby Valve & Gage Co.David Thibault Crosby Valve & Gage Co.Rolland Huffman Dresser IndustriesSteve Hart Duke Power Co.Jack Wade Entergy OperationsWillard Roit General Electric CompanyWilliam Phillips Omaha Public Power DistrictRichard Langseder Target Rock CorporationRichard Simmons Tennessee Valley AuthorityBarry Catanese Toledo Edison Co.Peter Seniuk Toledo Edison Co.John O’Neil Toledo Edison Co.Mary Wegner USNRCTom Nederostek Westinghouse ElectricKerry Craft Wisconsin Electric Co.Patrick Turrentine Wyle Laboratories

Robert Gwinn and Jim Petro at the Seabrook Nuclear Power Station were instrumentalin providing technical input and relief valve failure analysis.

Particular thanks are extended to the staff of the following plants for their time andeffort in support of the site visits performed during this project:

North Atlantic Energy Service Co., Seabrook Nuclear Power StationToledo Edison, Davis-BesseNiagara Mohawk, Nine Mile Point Unit 2Baltimore Gas & Electric, Calvert Cliffs Nuclear Power Plant

Finally, the support of the following utilities, manufactures, and test facilities wasinvaluable both for technical clarifications, supplying the technical manuals, drawings,procedures and information, and/or allowing on site visits to support the guide’sdevelopment and content.

Omaha public Power District, Fort Calhoun Nuclear StationTennessee Valley Authority, Corporate Maintenance SupportCrosby Valve & Gage CompanyDresser Industries

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Furmanite, Inc.G. E. Nuclear EnergyTarget Rock CorporationThe National Board of Boiler and Pressure Vessel InspectorsWestinghouse ElectricWyle Laboratories

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CONTENTS

Section No. Page No.

1.0 SYMBOLS AND ABBREVIATIONS................................................................................................ 1-1

2.0 SUMMARY ...................................................................................................................................... 2-1

3.0 INTRODUCTION ............................................................................................................................. 3-1

3.1 Purpose ..................................................................................................................... .......... 3-1

3.2 Organization of This Guide ................................................................................................ 3- 2

4.0 TECHNICAL DESCRIPTION OF PRVS ......................................................................................... 4-1

4.1 Types of PRVs and Functional Descriptions ................................................................... 4-14.1.1 General Description ................................................................................................. 4-14.1.2 PRV Design Theory ................................................................................................. 4-54.1.3 Safety Relief and Relief Valves .............................................................................. 4-144.1.4 Operational Characteristics of PRDs ..................................................................... 4-21

4.2 Nuclear Power Plant PRVs............................................................................................... 4-244.2.1 Pressurizer PRVs .................................................................................................. 4-254.2.2 BWR Main Steam Service PRVs ........................................................................... 4-374.2.3 PWR Pressurizer Power-Operated Relief Valves (PORVs) ................................... 4-474.2.4 PWR Secondary System Main Steam Safety Valves (MSSVs) ............................. 4-564.2.5 Auxiliary and Secondary System/BOP Safety Relief and Relief Valves ................ 4-60

5.0 FAILURE MODES AND FAILURE CAUSE ANALYSIS ................................................................. 5-1

5.0 Introduction ................................................................................................................ ......... 5-1

5.1 Failure Mode and Cause Analysis ..................................................................................... 5-1

5.2 Failure Mode and Cause Classification ............................................................................ 5-35.2.1 Failure Modes .......................................................................................................... 5-35.2.2 Failure Mode Causes............................................................................................... 5-4

5.3 Safety and Relief Valve Failure Data ................................................................................. 5-65.3.1 BWR MSS/Relief Valve Failures .............................................................................. 5-75.3.2 PWR Pressurizer Safety Valve Failures ................................................................ 5-105.3.3 PWR MSSV Failures ............................................................................................. 5-125.3.4 PWR PORV Failures ............................................................................................. 5-145.3.5 Relief Valve Failures .............................................................................................. 5-14

5.4 Failure Modes Analysis .................................................................................................... 5- 16

5.5 Causes of Failure Analysis .............................................................................................. 5-175.5.1 Aging...................................................................................................................... 5-185.5.2 Disc-to-Seat Bonding ............................................................................................. 5-18

5.6 Failure Significance on Outage Durations ..................................................................... 5-19

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6.0 PRD TESTING ................................................................................................................................ 6-1

6.1 Codes Governing Safety-Related PRV Testing ................................................................ 6-1

6.2 Codes Governing Non-Safety-Related PRV Testing ........................................................ 6-26.2.1 Allowable Overpressure ............................................................................................... 6-2

6.3 General Test Requirements ............................................................................................... 6-36.3.1 Test Methods ........................................................................................................... 6-36.3.2 On-Site Bench Testing ............................................................................................. 6-46.3.3 Auxiliary Lift Devices (ALDs) ................................................................................... 6-56.3.4 Developing a Repeatable Test ................................................................................. 6-6

6.4 In Situ Testing ............................................................................................................. .......6-116.4.1 ALDs ....................................................................................................................... 6-11

6.5 Testing for Ambient Temperature Conditions ................................................................ 6-156.5.1 Thermal Profile Mapping........................................................................................ 6-156.5.2 Temperature Profile ............................................................................................... 6-17

6.6 Pilot-Operated Relief Valves ............................................................................................ 6-17

6.7 Setpoint Drift .............................................................................................................. ....... 6-18

7.0 HANDLING AND SHIPPING OF SAFETY AND RELIEF VALVES ............................................... 7-1

7.1 Handling of Safety and Relief Valves ................................................................................ 7-17.1.1 Typical Rigging and Handling Instructions: Target Rock Safety

and Relief Valves (Including Valve Auxiliary Equipment Removal) .......................... 7-27.1.2 Typical Rigging and Handling Instructions: Consolidated, Crosby, and

Dresser Safety and Relief Valves ............................................................................ 7-87.1.3 PRD Cleanliness Control Instructions (at Workstation or Maintenance Shop) ...... 7-137.1.4 PRD Storage.......................................................................................................... 7-14

7.2 PRD Shipping to an Off-Site Vendor for Inspection and Testing ................................. 7-147.2.1 PRD Preparation for Shipment .............................................................................. 7-157.2.2 PRD Valve Receipt (Typical) .................................................................................. 7-187.2.3 PRD Packaging and Return Shipment Preparation ............................................... 7-197.2.4 PRD Documentation and Procedures.................................................................... 7-207.2.5 PRD QA Requirements .......................................................................................... 7-21

8.0 MAINTENANCE AND PERFORMANCE TRENDING .................................................................... 8-1

8.1 Predictive Maintenance and Inspection ........................................................................... 8-18.1.1 Parts Control ............................................................................................................ 8-18.1.2 Visual Inspection ...................................................................................................... 8-28.1.3 Acoustic Monitoring ................................................................................................. 8-48.1.4 Temperature Monitoring ........................................................................................... 8-4

8.2 Trending Safety and Relief Valve Performance and Maintenance History .................... 8-68.2.1 Safety and Safety Relief Valve Performance and Maintenance Trending ............... 8-68.2.2 NPRDS Trending and Failure Codes ....................................................................... 8-88.2.3 Trending and Analysis of Adverse Conditions ......................................................... 8-9

8.3 Preventive Maintenance (PM) and Inspection.................................................................. 8-98.3.1 Valve External ........................................................................................................ 8-108.3.2 Valve Internals ....................................................................................................... 8-13

8.4 Generic Corrective Maintenance ..................................................................................... 8-338.4.1 Lapping .................................................................................................................. 8-33

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8.5 PRV Control Rings and Their Settings .......................................................................... 8-42

8.6 Disassembling and Assembling Typical PRVs .............................................................. 8-438.6.1 Disassembling and Assembling Pressurizer Safety Valve ..................................... 8-438.6.2 General Information ............................................................................................... 8-45

8.7 Pressurizer Valve Disassembly ....................................................................................... 8-458.7.1 Remove the Cap .................................................................................................... 8-458.7.2 Record Ring Settings ............................................................................................. 8-458.7.3 Disassembly Retaining Spring Compression ......................................................... 8-458.7.4 Disassembly without Retaining Spring Compression ............................................ 8-48

8.8 Pressurizer Valve Assembly ............................................................................................ 8-498.8.1 General .................................................................................................................. 8-498.8.2 Assembly of Valve with Spring Compression Retained ......................................... 8-498.8.3 Assembling a Pressurizer PRV.............................................................................. 8-51

8.9 Disassembly and Assembly of MSSVs ........................................................................... 8-528.9.1 General Information ............................................................................................... 8-548.9.2 MSSV Disassembly ............................................................................................... 8-54

8.10 MSSV Assembly .............................................................................................................. .. 8-598.10.1 General .................................................................................................................. 8-598.10.2 Assembly of Valve (Spring Compression Not Retained) ....................................... 8-608.10.3 Assembly of Valve (Spring Compression Retained) .............................................. 8-61

8.11 Auxiliary PRVs ............................................................................................................. ..... 8-628.11.1 General Information ............................................................................................... 8-638.11.2 Disassembling Auxiliary PRVs .............................................................................. 8-648.11.3 Assembling Auxiliary PRVs .................................................................................... 8-678.11.4 Assembly ............................................................................................................... 8-678.11.5 Troubleshooting ..................................................................................................... 8-69

8.12 Summary .................................................................................................................... ....... 8-70

9.0 TRAINING AND PERSONNEL QUALIFICATIONS ........................................................................ 9-1

9.1 Codes and Standards for Training .................................................................................... 9-19.1.1 PTC-25.3 Training and Qualification Requirements ................................................ 9-19.1.2. OM-1 Training and Qualification Requirements ....................................................... 9-2

9.2 The NBBI.................................................................................................................... .......... 9-29.2.1 NB-65 Training and Personnel Qualifications .......................................................... 9-39.2.2 Repair Facility Certification ...................................................................................... 9-3

9.3 Site Training and Personnel Qualifications...................................................................... 9-49.3.1 Program Elements ................................................................................................... 9-49.3.2 Training Aids ............................................................................................................ 9-59.3.3 On-the-Job Training (OJT) ....................................................................................... 9-6

10.0 INDUSTRY DATA AND CONTACTS............................................................................................. 10-1

10.1 Safety and Relief Valve Testing Facilities ....................................................................... 10-1

10.2 Safety and Relief Valve Manufacturers ........................................................................... 10-2

10.3 ALD Manufacturers.......................................................................................................... . 10-4

10.4 Safety and Relief Valve Types, Applications, and Distribution .................................... 10-5

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APPENDIX A: SAFETY AND RELIEF VALVE MAINTENANCE GUIDELINE REFERENCES ............. A-1

United States Nuclear Regulatory Commission Documents .................................................... A-1Information Notices ............................................................................................................... A-1Generic Letters ..................................................................................................................... A-2

Bulletins and Reports .......................................................................................................... ......... A-2

Institute of Nuclear Power Operations (INPO) Documents ....................................................... A-2Significant Operating Experience Report (SOER) ................................................................ A-2Significant Experience Report (SER).................................................................................... A-2

Codes and Standards............................................................................................................ ........ A-3American Society of Mechanical Engineers ......................................................................... A-3

Vendor Technical Manuals ....................................................................................................... ..... A-4

EPRI Reports................................................................................................................... ............... A-4

Miscellaneous Publications..................................................................................................... ..... A-5

APPENDIX B: SELECTION, SIZING, AND INSTALLATION OF PRVS ................................................ B-1

1.0 Introduction ................................................................................................................ ......... B-1

2.0 Overpressure Protection.................................................................................................... B -1

2.1 Determining Required Relieving Capacity ....................................................................... B-1

2.2 System Allowable Valve for Overpressure (Certified Relieving) .................................... B-2

2.3 Determining Set Pressure .................................................................................................. B- 2

2.4 Set Pressure Tolerances .................................................................................................... B -3

2.5 Determining Blowdown ...................................................................................................... B- 7

3.0 Selecting PRVs .............................................................................................................. ..... B-7

4.0 Installation ................................................................................................................ ........... B-9

5.0 Sizing Relief Devices ....................................................................................................... ... B-9

APPENDIX C: ASME CODE TESTING REQUIREMENTS .................................................................... C-1

1.0 Code Requirements ........................................................................................................... . C-1

1.1 Test Frequencies ............................................................................................................ .... C-2

1.2 Test Methods ................................................................................................................ ....... C-2

1.3 Test Types .................................................................................................................. ......... C-31.3.1 Set Pressure ............................................................................................................ C-31.3.2 Blowdown ................................................................................................................ C-41.3.3 Capacity ................................................................................................................... C-41.3.4 Seat Tightness Testing ............................................................................................. C-5

2.0 ASME OM Code Mandatory Appendix I ............................................................................ C-6

2.1 Seat Leakage ................................................................................................................ ....... C-7

2.2 Setpoint Tolerance .......................................................................................................... .... C-8

2.3 Bellows Testing............................................................................................................. ...... C-9

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2.4 Testing Sequence ............................................................................................................ . C-10

2.5 Testing Frequencies ......................................................................................................... C-11

2.6 Requirements for Testing Additional Valves .................................................................. C-13

2.7 Test Media .................................................................................................................. ....... C-13

2.8 Testing at Inservice Ambient Temperature ..................................................................... C-13

2.9 ALDs ........................................................................................................................ .......... C-14

2.10 Personnel Requirements ................................................................................................. C-14

2.11 Test Instrument Requirements ........................................................................................ C-14

3.0 Documentation, Records and Record Keeping ............................................................. C-14

3.1 Records and Record Keeping ......................................................................................... C-14

APPENDIX D: AUXILIARY LIFT DEVICES ........................................................................................... D -1

1.0 Auxiliary Lift Devices ...................................................................................................... ... D-1

1.1 ALDs Used in the Industry ................................................................................................. D- 2

1.2 Crosby ALD Devices .......................................................................................................... D-31.2.1 Crosby ASPD ........................................................................................................... D-41.2.2 Crosby SPVD Model ................................................................................................ D-61.2.3 Dresser Hydroset ALD ............................................................................................. D-81.2.4 Trevitest Furmanite ALD .......................................................................................... D-91.2.5 AVK Industries ....................................................................................................... D-13

APPENDIX E: TEST BENCHES AND TEST SYSTEMS ....................................................................... E-1

1.0 Introduction ................................................................................................................ ......... E-1

2.0 Testing Techniques .......................................................................................................... .. E-1

3.0 Test Benches................................................................................................................ ....... E-5

4.0 Test Bench Arrangement ................................................................................................... E-5

5.0 Test System Design .......................................................................................................... .. E-8

6.0 Test Vessel Sizing .......................................................................................................... ... E-13

7.0 Typical Test Procedure ..................................................................................................... E -13

APPENDIX F: GLOSSARY .......................................................................................................... .......... F-1

1.0 Terms, Abbreviations, and Symbols ................................................................................. F-1

1.1 Glossary of Terms ........................................................................................................... ... F-1

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LIST OF FIGURES

Figure No. Page No.

4-1 Typical Safety, Safety Relief, and Relief Valve ....................................................................... 4-2

4-2 Typical Safety, Safety Relief, and Relief Valve ....................................................................... 4-3

4-3a Simple PRV Disc with Bevel Seat ........................................................................................... 4-6

4-3b Simple PRV with Enlarged Disc Area Outside of Velvel Seat that Providesan Additional Lifting Force ...................................................................................................... 4-6

4-3c Simple PRV with Huddle Chamber to Provide Pop Action and EnlargedDisc Area Outside of Bevel Seat that Provides an Additional Lifting Force ............................ 4-6

4-4 Typical Low-Lift Valve Design with Huddle Chamber and Adjusting Ring............................... 4-8

4-5 Typical Curtain Areas of Pressure Relief Valves ..................................................................... 4-9

4-6 (a-b) Pressure Relief Valve Control Rings ...................................................................................... 4-11

4-7 Typical Disc Lift Curve Crosby Style HC/HCA Safety Valve ................................................. 4-13

4-8 (a-b) Typical Safety Relief and Relief Valves................................................................................. 4-14

4-9 Typical Control and Huddle Chamber for Safety Relief and Relief Valves............................ 4-15

4-10 Effect of Backpressure on Set Pressure of a ConventionalSafety Relief and Relief Valve............................................................................................... 4-16

4-11 Piston-Type Pilot-Operated PRV .......................................................................................... 4-18

4-12 Diaphragm-Type Pilot-Operated PRV ................................................................................... 4-19

4-13 Power-Actuated Pressure Relief Valve (PORV) ................................................................... 4-20

4-14 Crosby Safety Valve.............................................................................................................. 4-26

4-15 Dresser Safety Valve ............................................................................................................ 4-27

4-16 Crosby Pressurizer Safety Valve, Style HB-BP .................................................................... 4-29

4-17 Dresser 31700 Safety Valve ................................................................................................. 4-31

4-18 Dresser Detail Showing Force Balance ................................................................................ 4-32

4-19(a-b) Target Rock Pilot-Operated Valve (Open) (a) and (Closed) (b) ............................................ 4-36

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Figure No. Page No.

4-20(a-b) Crosby Safety/Relief Valve (a) and Detail (b) ....................................................................... 4-39

4-21 (a-b) Dikkers Safety/Relief Valve (a) and Detail (b) ....................................................................... 4-42

4-22 (a-b) Target Rock Two-Stage Safety/Relief Valve (closed) ............................................................ 4-43

4-23 Target Rock Three-Stage Pilot-Operated Valve .................................................................... 4-46

4-24 Crosby (Model HPV-SN) PORV ............................................................................................ 4-48

4-25 Dresser Electromatic Relief Valve (Model 1525VX).............................................................. 4-50

4-26 Control Components PORV .................................................................................................. 4-51

4-27 Copes-Vulcan PORV ............................................................................................................ 4-52

4-28 Target Rock PORV................................................................................................................ 4-54

4-29 Crosby (Garrett), Right Angle PORV .................................................................................... 4-55

4-30 Crosby (Garrett), Straight Through PORV ............................................................................ 4-55

4-31 Crosby (Garrett), PORV Schematic Diagram ....................................................................... 4-56

4-32 (a-b) Typical Crosby Model HAFN MSSVs .................................................................................... 4-58

4-33 Typical Dresser Type 1700 MSSV ........................................................................................ 4-59

4-34 A Soft Seat in a Dresser PRV ............................................................................................... 4-62

4-35 Crosby Style JO and JB Safety Relief and Safety Valve ...................................................... 4-63

4-36 Crosby Style JOS and JBS Safety Relief and Relief Valve(Conventional and Balanced) ............................................................................................... 4-64

4-37 Crosby Style JMAK Liquid Relief Valve(Water Ring Design) ............................................................................................................. 4-65

4-38 Crosby Style JMB-WR Liquid Relief Valve............................................................................ 4-66

4-39 (a-b) Crosby Series 800 and 900, Omni Trim with Screwed Inlet and Outlet(Valve Is Also Supplied with Flanged Connections) .............................................................. 4-67

4-39 (c-d) Crosby Series 800 and 900, Omni Trim with Screwed Inlet and Outlet(Valve Is Also Supplied with Flanged Connections) .............................................................. 4-68

4-40 (a-b) Typical Dresser 1900 Series Safety Relief/Relief Valve........................................................ 4-69

4-41 Typical Farris 2600 Series Safety Relief/Relief Valve ........................................................... 4-70

5-1 (a-c) BWR Safety Relief Valve, Failure Modes and Causes ........................................................... 5-8

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Figure No. Page No.

5-1 (d-e) BWR Safety Relief Valve, Failure Modes and Causes ........................................................... 5-9

5-2 (a-b) PWR Pressurizer Safety Valve Failure Modes and Causes ................................................. 5-10

5-2 (c-d) PWR Pressurizer Safety Valve Failure Modes and Causes .................................................. 5-11

5-3 (a-b) PWR MSSV, Failure Modes and Causes .............................................................................. 5-12

5-3 (c-d) PWR MSSV, Failure Modes and Causes .............................................................................. 5-13

5-4 PWR PORV Failure Modes................................................................................................... 5-14

5-5 (a-b) Relief Valve, Failure Modes and Causes .............................................................................. 5-15

5-5 (c-d) Relief Valve, Failure Modes and Causes .............................................................................. 5-16

6-1 Force vs. DP Curve for an ALD............................................................................................. 6-13

6-2 Typical Thermocouple Placement ......................................................................................... 6-16

6-3 IR Thermography .................................................................................................................. 6-17

6-4 Schematic for Test Pilot Operated Relief Valves In Situ ....................................................... 6-18

7-1 Target Rock (Typical), Valve Assembly Hoisting (Valve on Header or Work Area) ................. 7-3

7-2 Target Rock (Typical), Pilot Assembly Hoisting (Valve on Header or Work Area) ................... 7-4

7-3 Target Rock (Typical), Pilot Valve Hoisting ............................................................................. 7-5

7-4 Target Rock (Typical), Base Assembly Hoisting (Valve on Header) ........................................ 7-6

7-5 Target Rock (Typical), Base Assembly Hoisting (Work Area) ................................................. 7-7

7-6 Target Rock (Typical), Main Valve Hoisting (Work Area) ........................................................ 7-8

7-7 “Typical” Safety and Relief Valve Lifting Locations ............................................................... 7-10

7-8 Typical Consolidated Electromatic Valve with Lifting Eyebolt ................................................ 7-11

7-9 Typical Crosby 6R10 Safety Valve with Hoisting Bracket ..................................................... 7-12

7-10 Crosby Hoisting Arrangement for Crosby 6R10 HB-BP Safety Valve ................................... 7-13

7-11 Typical Utility Design PRD Transport/Storage Container ...................................................... 7-16

7-12 Typical Utility Design PRD Transport/Storage Container ...................................................... 7-17

7-13 Typical Crosby PRD Packing Crate Construction for Crosby Pressurizer and MSSVs ........ 7-18

8-1 Lever Assembly Design ........................................................................................................ 8-12

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Figure No. Page No.

8-2 Match Marks ......................................................................................................................... 8-15

8-3 Typical Thrust Bearing Design .............................................................................................. 8-17

8-4 Typical Disc Assembly .......................................................................................................... 8-21

8-5 Typical Retainer Ring for Disc Insert .................................................................................... 8-22

8-6 Typical Disc Tolerances ........................................................................................................ 8-24

8-7 Typical Critical Dimension for Nozzle Seat ........................................................................... 8-25

8-8 Full-Nozzle Removal ............................................................................................................. 8-27

8-9 Stem Inspection .................................................................................................................... 8-29

8-10 Typical Disc/Top Guided System .......................................................................................... 8-30

8-11 Typical Spindle-Guided Bellows Valve and Bellows Testing ................................................. 8-32

8-12 Nozzle Relief Step ................................................................................................................ 8-34

8-13 Reconditioning Block ............................................................................................................ 8-38

8-14 Crosby Pressurizer Safety Valve .......................................................................................... 8-44

8-15 Hydraulic Jacking Device and Jacked Valve......................................................................... 8-47

8-16 Typical Crosby MSSV ........................................................................................................... 8-53

8-17 Illustrations of Nozzle Ring Setting and Guide Ring Level ................................................... 8-55

8-18 Illustration of MSSV (Jacked) and Location of Ring Setting Marking ................................... 8-56

8-19 Crosby Style JB-TD PRV ...................................................................................................... 8-63

8-20 Measurement for Spindle Nut and Adjusting Bolt ................................................................. 8-65

8-21 Typical Bonnet Assembly Torque Sequence ......................................................................... 8-68

D-1 ALD Principle of Operation ..................................................................................................... D-2

D-2 Crosby Air Set Pressure Device ............................................................................................. D-4

D-3 Generic Crosby Graph for Air Set Pressure Device ................................................................ D-5

D-4 Crosby Set Pressure Verification Device (SPVD) ................................................................... D-7

D-5 Dresser Hydroset .................................................................................................................... D-8

D-6 Furmanite Trevitest Apparatus .............................................................................................. D-11

xv



Figure No. Page No.

D-7 Mean Seat Diameter ............................................................................................................. D-12

E-1 Seat Tightness Test Setup ...................................................................................................... E-2

E-2 Set Pressure Test Setup ......................................................................................................... E-3

E-3 Solenoid Valve Test Setup ...................................................................................................... E-4

E-4 Actuator Test Setup................................................................................................................. E-5

E-5 Typical Air/N2 Test Bench Arrangement .................................................................................. E-7

E-6 Typical PRD Thermocouple Locations .................................................................................. E-10

E-7 Typical PRD Thermocouple Arrangement ............................................................................. E-11

E-8 Small Test Source ................................................................................................................. E-12

E-9 Large Capacity Test Source .................................................................................................. E-12

xvii



LIST OF TABLES

Table No. Page No.

4-1 PWR Safety Valve Sizes and Flow Rates ............................................................................. 4-34

5-1 PRD Failure Modes and Causes ............................................................................................ 5-2

5-2 NPRDS and LER Safety and Relief Valve Failures (1974–1993) ........................................... 5-7

6-1 Typical Valve Testing/Refurbishment Sequence ..................................................................... 6-4

6-2 Thermal Profile for a Pressurizer Valve (˚F) .......................................................................... 6-17

8 -1 Basic Principles of Parts Control ............................................................................................ 8-2

8-2 Test Results Useful for Determining PRV Maintenance........................................................ 8-13

8-3 Spring Assembly Inspection .................................................................................................. 8-19

8-4 Disc Removal Restrictions, Causes, and Effects .................................................................. 8-21

8-5 Disc Holder Failure Causes and Effect on PRV Performance .............................................. 8-23

8-6 Typical Improper Nozzle Tolerance Effects on Valve Performance and Tightness ............... 8-26

8-7 Full Nozzle Removal Criteria ................................................................................................ 8-26

8-8 Guiding System Troubleshooting Guide ............................................................................... 8-31

8-9 Lapping Compounds ............................................................................................................. 8-37

8-10a Operational Problems for Auxiliary Relief Valves .................................................................. 8-69

8-10b Seat Leak Problems for Auxiliary Relief Valves .................................................................... 8-70

10-1 Safety and Relief Valve Testing Facilities ............................................................................. 10-2

10-2 Safety and Relief Valve Manufacturers ................................................................................. 10-3

10-3 ALD Suppliers ....................................................................................................................... 10-4

10-4 Pressurizer Safety Valves and Distribution in PWR Plants ................................................... 10-5

10-5 Power-Operated Relief Valve Distribution in PWR Plants .................................................... 10-6

10-6 Crosby MSSV and PSV Installations at Domestic and International Utilities ........................ 10-7

xviii



Table No. Page No.

10-7 Nuclear Power Plants with Dresser Pressurizer Safety Valves .......................................... 10-12

10-8 Nuclear Power Plants Using Target Rock Safety Valves .................................................... 10-13

B-1 PRD Operating RequirementsASME Boiler and Pressure Vessel Code Summary ............................................................... B-4

C-1 Class I - Safety Valve Performance Tolerances ...................................................................... C-1

C-2 Seat Tightness Testing Methods for Pressure Relief Devices ................................................ C-8

C-3 Manufacturer’s Setpoint Tolerances—Safety Valves .............................................................. C-9

C-4 Manufacturer’s Setpoint Tolerances—Safety Relief Valves and Relief Valves ....................... C-9

C-5 Test Requirements and Sequence ........................................................................................ C-11

C-6 Section XI / PTC 25.3 and OM Code—General Comparison Chart ..................................... C-16

D-1 ALDs Used by the Industry ..................................................................................................... D-3

1-1



1SYMBOLS AND ABBREVIATIONS

ADS Automatic Depressurization SystemASME American Society of Mechanical EngineersB&PV Boiler and Pressure VesselBTU/hr British Thermal Units per HourBWR Boiling Water ReactorCFR Code of Federal RegulationsDEG. DegreeDOT Department of Transportationxxx˚ Degree (circumference)In. InchesID IdentificationINPO Institute of Nuclear Power Operationslbs Pounds (Weight)lbs/cu.ft. Pounds per Cubic Footlb/hr Pounds per HourkHz. KilohertzMW MegawattNRC Nuclear Regulatory CommissionNMAC Nuclear Maintenance Applications CenterNUREG Nuclear RegulationsPM Preventive MaintenancePORV Power Operated (Actuated) Relief Valvepsi Pounds per Square Inch (Pressure)psia Pounds per Square Inch Absolute (Pressure)psig Pounds per Square Inch Gage (Pressure)PWR Pressurized Water ReactorQC Quality ControlQTY Quantity˚R Degree RankineRCS Reactor Coolant SystemRMS Root Mean Squaresq. ft. Square Feet

2-1



2SUMMARY

This guide is designed as an aide for power plant personnel responsible for the mainte-nance of safety and relief valves. The guide can also be effectively used by traininginstructors to develop course materials.

The technical description section defines the various types of safety devices used in thenuclear industry and details their operating principles and applications. Specifically, theoperational characteristics of Crosby Valve and Gage Company (Crosby), DresserIndustries (Dresser), and Target Rock Corporation (Target Rock) valves used in theprimary and the balance-of-plant (BOP) systems of boiling water reactor (BWR) andpressurized water reactor (PWR) type power plants are covered in detail. Vacuumbreakers and nonreclosing-type devices (rupture discs, fusible plugs, etc.,) are notincluded in this document.

A failure mode and cause analysis section provides information on the reported failuresfrom the Nuclear Plant Reliability Data System (NPRDS) and License Event Report(LER) databases by valve types and their causes. A generic table identifies the variousvalve failure modes and probable causes.

The section on testing provides a review of ASME Code requirements along with guide-lines on bench testing and testing with auxiliary-lift devices (ALDs). Effect of environ-ment on the test results is highlighted.

A section on maintenance provides recommendations on predictive and preventivemaintenance (PM). Recommended methods of disassembly, corrective repair, inspec-tion, re-assembly, and performance monitoring are included.

In addition, the guide includes other useful sections and appendices on topics likeshipping and handling, valve sizing, ASME Code requirements, types of valves used invarious nuclear power plants, manufacturers of valves and testing equipment.

3-1



3INTRODUCTION

Safety and relief valves are pressure relief devices (PRDs) used for overpressure protec-tion of equipment in power plants. In nuclear power plant applications a high demandof reliability is placed on these devices. The valves may be required to open for accident(overpressure) mitigation and reseat after the system pressure is reduced and returnedto normal operating conditions. Because it is critical for these valves to operate withincertain specifications, this guide has been developed to provide background on thedesign, selection, application, maintenance, repair, refurbishment and testing of PRDs.

3.1 Purpose

This guide provides general information on the following types of PRDs, namely pres-sure relief valves (PRVs):

• Safety valves

• Power-operated relief valves (PORVs)—direct-acting and pilot-actuated

• Safety relief valves—safety valves with auxiliary-actuating devices

• Relief valves

NOTE: The terms “valve,” “PRV,” and/or “PRD” have been used in the generic sensethroughout this guide. When referring to specific valve types, the designations given in theglossary have been used.

This guide is written to provide necessary general information and guidance to plantpersonnel responsible for PRVs. Maintenance engineers, system engineers, and mainte-nance support personnel should also find this document to be an important resource inpreparing and updating plant procedures, and providing technical direction to thosewho perform these activities. Training staff should also find this guide useful in prepar-ing training material.

This guide also contains information on a variety of PRVs used in nuclear power plantapplications. It is realized that when a guide of this type is prepared, it cannot cover alltypes of PRVs manufactured and used for nuclear power plant applications. It is theintent, however, that this guide will provide a broad overview of PRDs, their applica-tion, and maintenance.

3-2



Further, it is cautioned that this document is a guide. When specific information isneeded the manufacturer’s information should always be used.

3.2 Organization of This Guide

This guide is divided into ten sections with the information from the previous sectionsleading into the development of the later sections. Therefore, persons being introducedinto the field of safety and relief valves should read this manual from the beginning. It isimportant to note that this guide is designed to provide a general overview on PRDs,and the reader is reminded that when maintenance and testing is being performed on aPRD, the instruction manual provided by the manufacturer must be used. Experiencedtechnicians looking for specific information may go to the topical chapter on the subject.Several appendices are included and provide additional advanced information. Thereference section provides an exhaustive listing of various documents on this topic pub-lished by the industry, manufacturers, and regulatory bodies.

Section 1 Symbols and Abbreviations

Section 2 Summary

Section 3 Introduction and purpose of this guide

Section 4 Generic technical description of the different types of PRVs addressed inthis guide and an overview of the types of PRVs and their applications.Specific detail technical information for any valve should always beobtained from the valve manufacturer.

Section 5 Detailed failure modes and cause analysis that addresses the importantfailure modes for safety valves in the nuclear industry. The results of thisanalysis are used to focus attention on the significant testing and mainte-nance issues that adversely affect the performance of safety valves.

Section 6 Methods used to test PRDs for set pressure, seat leakage, and blowdown.

Section 7 General information on the handling and shipping of PRDs.

Section 8 General information on the maintenance of typical PRVs. This section isdesigned to give the reader a general overview of typical maintenanceactivity.

Section 9 Guidelines for the training of personnel and also for personnel and facil-ity qualifications for testing and maintaining safety valves.

Section 10 Industry data and vendor contacts that are useful in acquiring and ex-changing information relating to safety valve maintenance and testing.

3-3



Appendix A Safety and Relief Valve Maintenance Guideline References

Appendix B Selection and Sizing of Safety Valves

Appendix C ASME Code Testing Requirements

Appendix D Auxiliary Lift Devices

Appendix E Test Benches and Test Systems

Appendix F Glossary lists and defines PRD terms used in the guide that are consistentwith current ASME Code terminology to establish a consistent startingpoint.

4-1



4TECHNICAL DESCRIPTION OF PRVS

Section 4.0 is designed to assist engineers and plant maintenance personnel understandthe basic principles and operating mechanisms of different types of PRVs. The term“valve” and “pressure relief valve” (PRV) and “pressure relief device” (PRD) will beused generically throughout this guide to describe all types of safety and relief valves.A thorough understanding of principles and operating mechanisms of the PRVs willhelp with the interpretation and understanding of the subsequent sections on failuremechanisms, valve applications, maintenance, and testing recommendations. Non-reclosing type PRDs, like rupture discs and relief valves used for vacuum, are not in-cluded in the scope of this guide.

Readers of this section will receive the most benefit by first perusing the general de-scription section and then proceeding to the section(s) most applicable to their need.

4.1 Types of PRVs and Functional Descriptions

4.1.1 General Description

A PRV is designed to prevent internal fluid pressure from rising above a predeterminedmaximum in a pressure vessel. PRDs can be reclosing or non-reclosing types. As thename implies, a reclosing type device is expected to open to relieve excess pressure andthen automatically reclose allowing the vessel pressure to return to normal operatingpressure and system operation to resume. Spring-loaded, safety relief valves are used asreclosing type pressure relieving devices. The terms “safety valves” and “PRVs” aregenerally used interchangeably.

A spring-actuated, reclosing-type device may also be used to prevent excessive internalvacuum in a vessel. These are known as vacuum relief valves (vacuum breaker valves).A non-reclosing PRD is designed to remain open after relieving excess pressure. Fusibleplugs and ruptured discs are examples of this type of device. The scope of this guidewill be limited to the reclosing type of pressure relieving devices or PRVs. As such, non-reclosing devices or vacuum relief valves will not be discussed.

PRVs are critical devices for power plant operation, and in a nuclear plant they may besafety-related or non-safety-related. Personnel assigned to maintain the valves shouldfully understand valve construction, operation, and maintenance to ensure that thedevices perform intended overpressure protection functions when needed.

4-2



The different types of self-actuated PRVs are described below and shown in Figures 4-1and 4-2. (Note that these figures are identical to the PRVs shown in ASME Section IIISubsection NB; NC; and ND in Figure NX-3591.1-1 and NX3591.2.)

Open Bonnet

Cap

Adjusting Screw

Bonnet (closed)

Spring Washers

Spindle (stem)

Spring

Balancing Piston(if required)

Bellows(if required)

Guide

Disk

SecondaryPressure Zone

Control Rings

Body

PrimaryPressure Zone

Nozzle

INLET

VALVESEAT

OUTLET

Yoke or Bonnet

Figure 4-1Typical Safety, Safety Relief, and Relief Valve

4-3



Cap

AdjustingScrew

Bonnet(closed)

SpringWashersSpring

Spindle(stem)

Guide

Secondarypressure zone

Control rings

VALVE SEAT Body

Primary pressure zone

Nozzle

Disk

INLET

OUTLET

OUTLET

INLET

VALVESEAT

Figure 4-2Typical Safety, Safety Relief, and Relief Valve

To ensure the reader uses ASME Code terminology, a review of terms begins below.

Safety Valve. An automatic PRD actuated by the inlet static pressure and characterizedby a rapid opening pop action. The valve is used for gas and vapor service. Generallythis type of valve is used for steam service and is of an exposed spring design (openbonnet or housing) similar to the main steam safety valve (MSSV) on a PWR. This valvemay also be an enclosed spring design (closed bonnet or housing) similar to a pressur-izer safety valve on a PWR plant. Operational criteria (set pressure and overpressure)and blowdown for these valves by the ASME Code is more stringent than other PRVs.

4-4



Safety Relief Valve. A PRV characterized by a rapid opening pop action or by openingin proportion to the increase in pressure over the opening pressure depending on theapplication. The valve may be used for liquid or compressible fluids. In nuclear powerplants, a safety relief valve is generally used on secondary or auxiliary systems to pro-tect vessels and systems from overpressure. The design is such that the spring is en-closed inside the valve housing or bonnet, and the valve outlet typically discharges intoa closed system such as a suppression pool, collection tank, or receiver.

• Conventional Safety Relief Valve: A PRV that has its spring housing vented to thedischarge side of the valve. The operational characteristics (opening and closingpressure and relieving capacity) are directly affected by changes of backpressure onthe valve.

• Balanced Safety Relief Valve: A PRV that incorporates a means to minimize the effectsof backpressure on the operational characteristics.

Relief Valve. A PRV actuated by inlet static pressure having a gradual lift generally inproportion with the increase in pressure over the set pressure. It is used primarily forliquid service. As the inlet pressure increases, a liquid relief valve gradually opens torelieve the excess fluid. The valve then gradually recloses as the pressure decays belowthe opening pressure. In nuclear power plants, a relief valve is usually used for thesame types of systems as a safety relief valve except the inlet fluid is a liquid. It can besupplied in a conventional or balanced design.

Typical external pieces of a PRV (Figure 4-1 and 4-2) consist of a body, bonnet (or yoke),and a cap. Pieces located inside the body and bonnet and cap, include a spindle (orstem), a spring, spring washers, and adjusting screw. The adjusting screw determinesthe spring tension for the desired set pressure. The pieces located inside the valve arethe guide, disc, disc holder, nozzle and control rings, and if required, a bellows andbalancing piston.

PRVs characteristically have multipressure zones within the valve, that is, a primarypressure zone and secondary pressure zone (see Figure 4-1 and 4-2). The inlet is theprimary pressure zone and is part of the valve that is in actual contact with the pressuremedia in the pressure vessel and are called the pressure containing parts (nozzle to thevalve seat and disc). The outlet (beyond the valve seat) is the secondary pressure zone.Parts in this zone are: 1) pressure retaining members, parts that are stressed due to theirfunction of holding one or more pressure containing members in position and 2) partsthat have no structural function but are required to achieve performance

The most common element in all PRVs is the spring. The spring applies the force re-quired to keep the disc seat in contact with the nozzle seat. It also establishes the re-quired force that determines the valve set pressure (based on the seat area). The springalso provides a resisting force that, when combined with the forces developed in thehuddle and control chamber, which is beyond the valve seat, controls the disc lift andvalve closing.

4-5



4.1.2 PRV Design Theory

Thus far in this guide, one critical part of the valve, namely the spring, has been re-viewed. Other pieces in a PRV are also critical as they control (in combination with thespring) the operational characteristics and rated capacity. To better understand of thecontrols of the PRV types discussed, a review of the design features of the pieces thatmake up the valves’ huddle/control chamber follows.

Figure 4-3 is an illustration of simple PRVs:

• Figure 4-3a is a valve with a bevel seat.

• Figure 4-3b shows a valve identical to Figure 4-3a but with an enlarged disc area thatprovides an additional lifting force after opening.

• Figure 4-3c shows a combination of Figures 4-3a and 4-3b but with a huddle chamberlocated beyond the valve seat for the purpose of generating a pop action (on com-pressible fluids).

4-6



INLET

Valve Seat (Bevel)

Figure 4-3aSimple PRV Disc with Bevel Seat

INLETINLET

EnlargedDisc Area D I S C D I S C

Figure 4-3bSimple PRV with Enlarged Disc Area Outside of Bevel Seat

that Provides an Additional Lifting Force

INLETValve Closed

Huddle Chamber D I S C D I S C

INLET Valve Opened

Figure 4-3cSimple PRV with Huddle Chamber to Provide Pop Action and Enlarged Disc Area

Outside of Bevel Seat that Provides an Additional Lifting Force

4-7



Control features of this type are incorporated in most PRV/SV designs that are gener-ally categorized as follows:

• Low-Lift Safety Valve: A safety valve in which the actual discharge area (used todetermine the valve capacity) is determined by the position of the disc (see glossaryfor definition of “curtain area”).

• Full-Lift Safety Valve: A safety valve where the actual discharge area is not deter-mined by the position of the disc (see glossary for definition of “actual dischargearea”).

• Full-Bore (Nozzle Type) Safety Valve: A safety valve where there is no protrusion intothe bore of the valve and where the disc lifts sufficiently so that the minimum area atany section at or below the disc seat does not become the controlling orifice. Gener-ally this type of valve is defined as “reaction type” since the flow path of the fluidwhen the disc is in the open position reverses direction.

The three basic types of valve designs, low-lift, full-lift, and full-bore have been de-scribed. A review of each basic design, how it incorporates the features described inFigure 4-3, and how they operate follows.

4.1.2.1 Low-Lift Valve Designs

In a low-lift valve design, the disc travel (lift) is generally less than the nozzle bore area.As a result, the flow rate (capacity) of the valve is determined by the disc lift. Low-liftdesigns usually have a huddle chamber located past the valve seat (see Figure 4-3c and4-4). The huddle chamber entraps fluid as it escapes past the seat, thus, exposing thelarger disc area to pressure. The escaping fluid entrapped prior to the valve opening/popping causes an incremental upward force unbalance (pressure is now acting over alarger area of the disc than when it was fully seated). This additional upward force causesthe valve to open (pop on a compressible fluid).

The huddle chamber controls the pop action of the valve and can be fixed or variedthrough a moveable valve piece (such as an moveable ring).

The design of this chamber and the contour of the flow path in these pieces and thespring are combined to establish the valve operational characteristics (opening, lift,closing/blowdown). These designs generally achieve a low-lift as the secondary areaincreases with disc lift. The certified rated capacity, therefore, is determined based ondisc lift at the rated overpressure. This lift is used to calculate the curtain area and thecurtain area which is then used in the flow rate formula to determine the rated capacityfor the valve design.

Typical curtain areas of a PRV are shown in Figure 4-5.

4-8



VALVE CLOSED

DISKpressure causingforce unbalance

RIN

G

HUDDLE CHAMBERN

OZ

ZLE

VALVE SEAT

SEAT DIAMETER

FLOW VALVE INLET

(a)

DISK

RIN

G

NO

ZZ

LEDISC LIFT

(b)

Figure 4-4Typical Low-Lift Valve Design with Huddle Chamber

and Adjusting Ring

4-9



L = lift

D = seat diameter = smallest diameter at which seat touches disk

DB = other diameter of frustrum of cone

B = slant height of frustrum of cone

θ = seat angle = angle of seating surface with axis of valve

R = radius

GENERAL NOTE: Curtain area is the discharge area unless the disk attainssufficient lift for the valve bore to become the controlling area.

Flat-Seated ValveCurtain area = surface of cylinder = πDL

Bevel-Seated ValveCurtain area = surface of frustrum of cone = πB

D + DB 2


D + DB 2


D + DB 2

Radial-Seated ValveCurtain area = surface of frustrum of cone = πB

D + DB 2

Radial-Seated Valve Curtain area = surface of frustrum of cone = πB

D + DB 2

Figure 4-5Typical Curtain Areas of Pressure Relief Valves

4-10



4.1.2.2 Full-Lift Safety Valve Designs and Full-Bore Safety Valves

In full-lift and full-bore safety valves, the huddle chamber and the enlarged disc area areused to achieve the opening pop action. The actual discharge area, however, is not deter-mined by the disc lift since the disc lift area exceeds the actual nozzle discharge area.

These generally reaction-type designs (Figure 4-6) use a single-ring or two-ring controlconstruction to achieve the desired valve performance (opening, disc lift, and closingcharacteristic).

4.1.2.2.1 Reaction Type Design PRVs

In a reaction-type design PRV (see Figures 4-6a and 4-6b), the discharged fluid reversesdirection (approximately 180˚) from the position of entry into the valve.

As in low-lift designs, fluid initially escapes into the huddle chamber exposing a largerarea of the disc to system pressure. This causes an incremental change in the upwardforce and overcompensates the spring force and the valve opens/pops. Disc lift at popis dependent upon the valve control chamber contour, flow path, and spring force. Withthe disc in the open position, the flow path of the fluid is reversed (turning approxi-mately 180˚). Consequently, the momentum (reaction force) effect from the change inflow direction combined with the pressure (force) of the fluid acting across the discsurface further enhances the disc lift. These effects combine to allow the disc to achievemaximum lift and the valve to achieve maximum flow within allowable overpressurelimits. Final disc lift is determined at the overpressure at which the valve is capacityrated.

4.1.2.2.2 Two-Ring and Single-Ring Controls in Reaction-Type Design PRVs

Performance characteristics of reaction-type PRVs is determined by the huddle/controlchamber contour (flow passage) past the valve seat and the valve spring. This flowpassage contour is commonly combined with an adjustment feature called “rings” (seeFigure 4-6) (i.e., blowdown (upper) ring and/or nozzle ring).

The PRV can be of a single-ring or two-ring design. The nozzle ring in the two-ringdesign controls the valve opening characteristics. In the single-ring design, the nozzlering also controls the valve blowdown. On a two-ring valve, the blowdown is con-trolled by the blowdown ring.

4-11



SAFETYVALVE

CLOSED

DiskBlo

wdo

wn

Rin

g

HUDDLE CHAMBERN

ozzl

eR

ing

Noz

zle

INLET OPEN

Disk

Blo

wdo

wn

Rin

g

Noz

zle

Rin

g

Noz

zle

INLET

3

Closed

Disk

HUDDLE CHAMBER

INLET

Noz

zle

Rin

g

Noz

zle

INLET

Disk

Open

(a)

(b)

Noz

zle

INLET

Noz

zle

Rin

g

Blo

wdo

wn

Rin

g

PRIOR TOPOP

Disk

2

VALVE SEAT(FLAT)

1

2

Noz

zle

Rin

g

Noz

zle

VALVE SEAT(FLAT)

1

Figure 4-6 (a-b)Pressure Relief Valve Control Rings

4-12



Valve performance on a compressible fluid (steam, gas) with the rings set in the properlocation would cause the valve to open with minimum warning and close with a sharpaction and blowdown would be within the requirements of the Code or specification towhich it was manufactured. Adjustments to the rings would have one or a combination ofthe following effects:

Blowdown Ring:

• Lowering: Increases blowdown (reseat at a lower inlet pressure)

• Raising: Decreases blowdown (reseat at a higher inlet pressure)

Nozzle Ring:

• Lowering: Increases warning, reduces blowdown (on single-ring control)

• Raising: Decreases warning, increases blowdown (on single-ring control), causeshang on close.

The two-ring type control is primarily used in safety valves in steam service where theASME or other codes and standards require valve operation for set pressure, overpres-sure, and blowdown to be within close limits. The independent adjustment of each ringwill provide this performance.

In the single-ring control, the disc (or disc ring) contour becomes a fixed blowdown ringlimiting the valve adjustment for performance. This type of control is generally usedwhere the ASME or other codes or standards to which the valve is manufactured permitbroader operational requirements for set pressure, overpressure, and blowdown.

With the above background of PRV designs and understanding of the valve controls, areview of a typical opening and closing cycle of a PRV on steam can be discussed.

Figure 4-6(a-1) shows a two-ring control safety valve in the closed position. When inletpressure is increased to the set pressure, inlet fluid escapes across the valve seat andinto the huddle chamber. This escaped fluid pressure now acts over a larger area on thedisc ((see prior to pop Figure 4-6(a-2)). The additional upward force caused by this fluidpressure now exceeds the downward force of the spring. At this point the valve willpop and the disc will move vertically upward away from the nozzle (seat). The valvewill now be in the open position with the inlet fluid reversing direction and flowingbetween the inside diameter (ID) of the blowdown ring and the outside diameter (OD)of the nozzle ring ((Figure 4-6(a-3)). If the inlet pressure increases above the set pressureto the rated overpressure, the valve disc will lift further and at this rated overpressure,discharge its rated capacity. As pressure in the vessel and in the valve inlet decay, thevalve disc lift will decrease slightly. When the inlet pressure is at the reseat pressure, thedisc will reestablish a contact with the nozzle seat. The difference between the valveactual popping pressure and actual closing reseat pressure is defined as blowdown.

4-13



A typical lift curve for a Crosby style HC/HCA safety valve is shown in Figure 4-7. It isimportant to note that the lift characteristics (curves) for different PRVs may change.This is because of :

• The valve manufacturer

• The design

• The fluid (compressible or non-compressible) at the valve inlet

Note that for this Crosby safety valve on steam service the disc lift:

• At pop (set pressure) is approximately 70% of full capacity lift.

• Disc lift continues to increase as inlet pressure increases until it moves through asecondary lift at approximately 3% overpressure where it achieves 100% capacity.

• On closing the disc moves downward through two closing steps (the initial andfinal) prior to reseat.

FULL CAPACITY LIFT CLOSES

SECONDARYLIFT

OPENS

POP LIFT

3%ACCUMULATION

4% MAXBLOWDOWN

INITIAL CLOSING

FINALCLOSING

4% BELOWSET PRESSURE

-3% -2& -1% SET +1% +2%PRESSURE

100%

80%

60%

40%

20%

0

%

OF

CAPACITY

LIFT

PRESSURE

Figure 4-7Typical Disc Lift Curve

Crosby Style HC/HCA Safety Valve

4-14



4.1.3 Safety Relief and Relief Valves

Safety relief and relief valves covered in the definition section of this maintenance guideare self-actuated PRVs and are generally provided with an enclosed spring housingsuitable for closed discharged system applications. The construction of a spring-loadedPRV consists of a valve inlet or nozzle mounted on the pressurized system, a disc heldagainst the nozzle to prevent flow under normal system operating conditions, a spring tohold the disc closed, and a body/bonnet to contain the operating elements. The springload is adjustable to vary the pressure at which the valve will open (see Figure 4-8).

CONVENTIONAL

(a)

BALANCED

(b)

Bonnet

Spring

Bonnet VentPlugged

Body

Disc

Nozzle

Bellows

Bonnet VentOpen

Figure 4-8 (a-b)Typical Safety Relief and Relief Valves

4.1.3.1 Safety Relief Valves (Primarily used for Compressible Fluids) and ReliefValves (Use for Non-Compressible Fluids)

The design of the control and/or huddle chamber involves a series of tradeoffs. If thedesign maximizes lift effort, then blowdown will be long. If the design minimizesblowdown, then the lift effort will be diminished. Many PRVs are, therefore, equippedwith a nozzle ring that can be adjusted to vary the geometry of the control chamber to

4-15



meet a particular system operating requirement. Relief valves may also, for liquid applica-tions, use a different control and huddling chamber contour. For the control and huddlingchamber see Figure 4-9 illustrating the difference in the control and huddle chamber of aCrosby safety relief valve (gas and vapor service) and relief valve (liquid service).

ControlChamber

NozzleRing

SetScrew

Nozzle

DiscHolder

Disc

CONTROL AND HUDDLE CHAMBER

SAFETY RELIEF VALVEGAS AND VAPOR SERVICE

(a)

RELIEF VALVELIQUID SERVICE

(b)

Figure 4-9Typical Control and Huddle Chamber for Safety Relief and Relief Valves

The safety relief valve is primarily used for gas and vapor service (compressible fluids)and the relief valve for liquid service (non-compressible fluids). Each PRV type ismanufactured as: 1) a conventional safety relief valve (Figure 4-8a) or 2) a balancedsafety relief valve (Figure 4-8b). The major difference is that the balanced valve incorpo-rates a means (such as a bellows) to minimize the effect of backpressure on the opera-tional characteristics (opening pressure, closing pressure and relieving capacity).

In the illustration shown in Figure 4-8b, the means used to minimize the effect ofbackpressure is the bellows. To better understand the application and operation of aconventional (non-bellows) and balanced (bellows) PRV, a review of the valves, theirapplications, and the effects of backpressure follows.

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PRVs on clean non-toxic, non-corrosive systems may be directly vented to the atmo-sphere. Valves that vent to the atmosphere, either directly or through short vent stacks,are not subjected to elevated backpressure conditions. In this application, a conven-tional PRV can be used. PRVs on corrosive, toxic or valuable recoverable fluids arevented into closed systems.

On installations where the PRV discharges into a closed system, or when a long ventpipe is used, there is a possibility of developing high backpressure. The backpressureon a PRV must always be evaluated. In this case, a balance PRV is used.

A review of a force balance on the disc (Figure 4-10) with the valve closed shows thatthe force of fluid pressure acting on the inlet side of the disc will be balanced by theforce of the spring. If pressure exists on the outlet side of the valve, the valve set pres-sure will increase. If pressure in the valve outlet varies while the valve is closed, thevalve set pressure will change. If backpressure varies while the valve is open and flow-ing, valve lift and flow rate through the valve can be affected. Care must be taken in thedesign and application of PRVs to compensate for these variations. Additional details ofconventional and balanced valves are discussed in the following sections.

DiskGuide Spring

Bonnet

P1

P2 P2

P2

P2 P2

Spr

ing

FS

DISK

Backpressure IncreasesSet Pressure

OUTLET

INLET

P1 AN = FS + P2 AN

Figure 4-10Effect of Backpressure on Set Pressure of a Conventional

Safety Relief and Relief Valve

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4.1.3.2 Conventional (Non-Bellows) Safety Relief Valves

Backpressure that may occur in the downstream system while the valve is closed iscalled superimposed backpressure. This backpressure may be a result of the valveoutlet being connected to a normally pressurized system or may also be caused by otherPRVs venting into a common header. Compensation for superimposed backpressurethat is constant may be provided by reducing the spring force. Under this condition, theforce of the spring plus the backpressure acting on the disc equals the force of the inletset pressure acting to open the disc. It must be remembered, however, that the value ofthe set pressure will directly vary with any change in backpressure.

4.1.3.3 Balanced (Bellows) Safety Relief Valves

When superimposed backpressure is variable, a balanced bellows design is recom-mended. A typical balanced bellows style valve is shown in Figure 4-8b. The bellows isdesigned with an effective pressure area equal to the seat area of the disc. The bonnet isvented to ensure that the pressure area of the bellows will always be exposed to atmo-spheric pressure and to provide a telltale sign should the bellows begin to leak. Varia-tions in backpressure, therefore, will have no effect on set pressure. Backpressure may,however, affect flow.

Backpressure that may occur after the valve is open and flowing is called dynamic orbuilt up backpressure. This type of backpressure is caused by fluid flowing from thePRV through the downstream piping system. Built up backpressure will not affect thevalve opening pressure, but may have an effect on valve lift and flow. Valve manufac-turers recommend that on applications of 10% overpressure, a balanced bellows designbe used when built-up backpressure is expected to exceed 10% of set pressure.

In addition to offsetting the effects of variable backpressure, the bellows acts to sealprocess fluid from escaping into atmosphere and isolates the spring, bonnet and guid-ing surfaces from contact with the process fluid. This is especially important for corro-sive services.

4.1.3.4 Pilot-Operated Pressure Relief Valves

Pilot-operated PRVs are not as commonly used as direct acting PRVs, but they havebeen applied in a wide variety of applications for many years. The primary differencebetween a pilot-operated PRV and a self-actuated PRV is that process pressure insteadof a spring is used to cause the main valve disc to stay closed or to open. A pilot orcontroller is used to sense process pressure and to pressurize or vent the dome pressurechamber causing the main valve to open or close.

There are two types of pilot-operated PRVs, piston (main valve disc—Figure 4-11) anddiaphragm (Figure 4-12). Both valve types consist of a main valve and a pilot. The pilot

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controls the pressure on the top side of the piston (main valve disc). A seat is part of oris attached to the lower end of this disc. The operation features are as follows:

• When the main valve is closed and inlet pressure is below the set pressure, thepressure on opposite (top) side of the main valve disc is equal.

• When the inlet pressure is increased to the pilot valve set pressure, the pilot opens,the cavity on the top side and the main valve disc is depressurized, and it strokesupward. This causes the main valve to relieve the inlet fluid pressure.

• When the inlet pressure decreases, the pilot closes causing the cavity on the top ofthe main valve disc to be repressurized, and the valve closes.

A piston-type, pilot-operated relief valve (Figure 4-11) uses a piston for the main valvedisc that has an O-ring or similar type seal at the upper end to maintain pressure in thecavity or dome above the main valve disc. The piston type valve can be used for pres-sure 15 psig to 10,000 psig.

Pilot

Dome

PistonSeal

Seat

Main Valve Disc(Piston)

PressurePickup

Main Valve

Outlet

Inlet

Figure 4-11Piston-Type Pilot-Operated PRV

The diaphragm type, pilot-operated relief valve (Figure 4-12) is similar to the pistontype except a flexible diaphragm is used to form a seal at the upper end of the mainvalve disc and to maintain pressure in the dome cavity (instead of a sliding O-ring seal).This diaphragm reduces the sliding friction force and permits valve operation at much

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lower inlet and set pressures than would be possible with a sliding seal. The diaphragmtype valve can be used from pressures of 2-inch water column (0.072 psig) up to 50 psig.

Pilot-operated valves are used for compressible and non-compressible fluids dependingupon the limits permitted by the ASME and/or other codes and should only be used onclean systems.

Dome

Pilot Valve

Diaphragm

Seat and MainValve Disc

Main Valve

Pressure PickupInlet

Outlet

(Process PressureValve Closed)

Figure 4-12Diaphragm-Type Pilot-Operated PRV

4.1.3.5 Power-Actuated PRVs (PORVs)

As covered in the definition section, the power-actuated PRV is a PRV in which themajor relieving device is combined with and controlled by a device that requires anexternal source of energy such as electrical, pneumatic or hydraulic. This PRV can beremotely operated by plant personnel or in response to signals from pressure or tem-perature-sensing devices. It offers the benefit of a wide variety of control systems, but

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has the disadvantage of relying on an external source of power that may fail underemergency conditions.

Descriptions of the various types of power-actuated PRVs are presented in Section 4.1.4.Figure 4-13 shows a typical schematic of a power-actuated PRV with the plug and ventseat in the closed position. With the plug and vent seat closed, inlet fluid pressure is in theactuator head chamber and is acting on the top surface of the plug piston area. This fluidenters past the supply seat.

Discharge Flow

Valve Seat

Plug

Inlet Flow

Piston Area

ActuatorHead Chamber

VentSeat

SupplySeat

SolenoidSpring

ElectricalSolenoid

Figure 4-13Power-Actuated Pressure Relief Valve (PORV)

When the solenoid is energized, the vent seat moves downward and seals against thesupply steam. This prevents the entry of inlet fluid pressure into the actuator headchamber. The actuator chamber pressure is at the same time vented past the vent seatand into the discharge. The plug now has higher pressure acting on the inlet piston areaand moves upward away from its seat. This action permits inlet fluid to flow to thevalve discharge. Plug closure is the reverse of the opening sequence.

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4.1.4 Operational Characteristics of PRDs

In the previous sections, different types of valve designs were reviewed and the ASMECodes were used to define valve types. Valve operations were also reviewed. The nextsection explains the operational characteristics, Code definitions, and how they areapplied to these valve designs.

4.1.4.1 Set Pressure and Lift (Disc)

The set pressure (opening pressure, popping pressure) is pressure where the valve dischas measurable movement in the opening direction to (lift) due to an inlet pressure. Thevalve lift begins when the inlet fluid pressure has increased to the point where theupward fluid force begins to exceed the downward force on the disc. In a spring-loaded, self-actuated PRV, the set pressure or opening characteristics of a PRV will varydepending upon the service fluid. For compressible fluid such as air, gas and steam, thevalve will open with a pop action. For a non-compressible fluid, such as water, openingwill occur with minimal disc lift, causing the valve to discharge a small, steady streamof liquid that increases with the inlet pressure. Depending upon the design of thehuddle chamber and the control passage, the disc lift may increase substantially at apressure value above the opening pressure with an equally substantial increase in flowrate and then increase further to the rated lift at the desired overpressure.

The ASME Codes, Section I and VIII and Subsections of ASME Section III NB, NC, NDand NE and valve design specifications require that PRVs open within certain set pressuretolerance limits depending upon valve service requirements and set pressure value. Itwould be prudent for the user to understand these requirements prior to a test procedure.

Ambient temperatures can affect the valve’s normal temperature profile. Large ambienttemperature transients may cause the valve to open outside expected lift set pressuretolerance. The valve setpoint should be tested at the opening ambient conditions of thevalve or if the valve is tested at room ambient conditions (inlet fluid and ambient).Correction in the valve set pressure for these conditions and for backpressure on aconventional valve must be made. This correction is called Cold Differential Test Pres-sure (CDTP).

Other variables that may affect the actual set pressure of the valve include:

• The physical condition of the valve and its parts including the condition of the valveseat

• The maintenance practices related to the valve

• The testing practices related to the valve

• The physical environment of the installed condition of the valve (such as ambientand fluid temperature, vibration, backpressure on conventional non-balancedvalves, etc.)

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4.1.4.2 Reseat Pressure and Blowdown

PRVs, after opening normally, close at a pressure that is below its setpoint and/oractual opening pressure and above the system’s normal operating pressure.

Closing pressure is a value of inlet static pressure at which the disc reestablishes contactwith the seat. The actual value of closing or reseat pressure is used with the actual valveopening pressure to calculate blowdown. Blowdown can be expressed in pressure unitsor percent and is calculated as follows:

Percent Blowdownactual set pressure actual closi pressure

set pressurex( ) =

−

= −

ng

Blowdown (pressure units) actual set pressure actual closing pressure

100

The blowdown requirements and/or reseating requirements for PRVs vary dependingupon the valve set pressure value and the valve service conditions. Consequently, theuser should understand these requirements.

Factors that can affect valve reseat pressure and blowdown are:

• Improper setting of valve control ring

• Changes in fluid and fluid temperature

• Improper testing practices

• Improper installation of the valve

4.1.4.3 Overpressure and Capacity

Overpressure is a pressure increase at the valve inlet that exceeds the set pressure of aPRV and is usually expressed as a percent of set pressure.

Example: If a PRV opened at 1000 psig to relieved fluid at 10% overpressure, the inletfluid pressure at the valve inlet would be 1100 psig.

The relieving capacity of PRVs is determined and rated at an overpressure permitted bythe applicable code or regulation to which the valve is rated capacity certified. Codesand standards credit each valve design with a portion of the actual measured capacity.

PRVs used in nuclear power plants are usually manufactured to ASME Codes Section I,III and VIII. These Codes specify the overpressure at which the valve design is capacityrated and provides formulas for establishing the portion of the actual measured flow thatis used as its rated capacity. It is this capacity (rated relieving or nameplate marked capac-ity) that is used as a basis for the selection and application of a PRD for overpressureprotection of a vessel or system.

To obtain a capacity certification such as ASME, the manufacturer submits the informa-tion on the valve design advising the ASME of the Code section (Section I, III, or VIII,

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etc.) and the fluid to be used. The valve design is then performance and capacity testedto the requirements of this Code and in accordance with safety and relief valve perfor-mance and test code ASME/ANSI PTC-25.3. After tests are successfully completed onthat fluid, a coefficient of discharge is established. This coefficient may be derateddepending upon the Code requirements. It is this value that is used with the ASMEformula to calculate the rated capacity.

Note: ASME PTC 25.3 has been revised as ASME PTC-25 in 1994.

The following is a typical formula for an ASME Section III Class 1 full-lift safety valveon steam service (below 1500 psig). The formula is used to determine the valve’s ratedcapacity after being certified (see ASME Section III, SubSection NB, Article NB-7000).

W = 51.45 APK

where:

W = rated flow lbs/hr. saturated steam (certified capacity)

A = actual discharge area through the valve developed lift, sq. in.

P = (set pressure x 1.03) plus atmospheric pressure, psia

K = coefficient of discharge (certified)

K = .9 KD

K

Actual FlowTheoretical FlowD =

NOTE: Users of PRVs are cautioned that when calculating PRV capacities, the code orstandard under which the valve is manufactured must be used to determine the rated capacity.

4.1.4.4 Chatter and Flutter

PRVs are designed to operate without chatter and flutter. Chatter is defined as the rapidreciprocating motion of the movable parts where the disc contacts the seat. Flutter is thesame as chatter, but the disc does not contact the seat. Chatter or flutter during valveoperation can cause damage to the valve internals and can occur on opening or closing.This malfunction of a PRV can be system or mechanically caused.

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System caused malfunctions are usually a result of poor inlet piping design or installa-tion of the valve in a poor location. A PRV on open will cause a rapid pressure decay atthe valve inlet. Since the valve is a force-balanced device, the combined pressure(dynamic and acoustic) decay rapidly below the valve’s normal closing pressure, caus-ing the disc lift to be reduced and the disc to move to the closed position. Because sys-tem pressure has not been reduced to a level that will permit complete disc closure,increased pressure at the valve inlet will cause the valve to reopen. When this occurs,the inlet piping to the valve should be reviewed for pressure losses and restrictions.

Mechanically caused malfunctions vary from:

• The incorrect PRV selection for the fluid and service condition, i.e. liquid valve forgas service or, conventional valve rather than a balanced valve for a backpressurecondition

• Poor valve maintenance practices that result in improper:

— Valve set pressure setting

— Setting of control/adjusting rings

— Valve assembly that could cause mechanical interference with the moving parts

4.2 Nuclear Power Plant PRVs

In the US, PWRs use self-actuated, spring-loaded valve design for the pressurizer safetyvalves. BWRs use either a self-actuated, pilot-operated safety valve design or a self-actuated, spring-loaded safety valve with a pneumatic cylinder that allows the valve tobe opened below the self-actuated set pressure for the main steam primary systemoverpressure protection. The pressurizer spring-loaded safety valves are manufacturedby Crosby Valve and Gage Company (Crosby) and Dresser Industries, Incorporated(Dresser). In addition to the spring-loaded, self-actuated safety valves, a self-actuated,pilot-operated valve is also used in pressurizer applications. The main steam PRVs on aBWR are pilot-operated safety valves manufactured by Target Rock or spring-loadedsafety valves manufactured by Crosby. These valves are generally designed and manu-factured to the requirements of ASME Section III Subsection NB Article NB-7000. Inaddition to the self-actuated type of PRVs, PWR plants use power-actuated PRVs pro-duced by a variety of valve manufactures. These valves are manufactured to ASMESection III, Subsection NB, Class 1 design requirements.

For the secondary system of PWR plants, self-actuated safety valves are used for over-pressure protection. These valves, as the pressurizer safety valves, are typically manu-factured by Crosby or Dresser. Finally, for the auxiliary and secondary systems andBOP applications, safety relief and relief valves are used. These PRVs (main steamsafety and auxiliary/secondary system) may be produced by a variety of manufacturersand are usually manufactured to the requirements of ASME Section III, Subsection NB,NC or ND, Class 2 or 3 or ASME Section VIII depending upon the system requirementsto which they provide overpressure protection.

The following section is an overview of these valve types.

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4.2.1 Pressurizer PRVs

4.2.1.1 General Description - Spring-Loaded PSVs

The Crosby and Dresser self-actuated, spring-loaded safety valves used for PWR pres-surizers are similar in design. A sketch of a typical Crosby safety valve is shown inFigure 4-14, and a typical Dresser safety valve is shown in Figure 4-15. A general opera-tional description of both valve designs and the design differences are discussed below.

PWR self-actuated, spring-loaded safety valves are mounted directly on the top of thepressurizer and are attached by flanged end connections. The inlet side of the valve isdesigned for reactor coolant system pressure and temperature. The outlet flange andpiping are designed for the lower outlet discharge pressure. The valve is maintained inthe closed position by the mechanical force of a compressed spring. This force is trans-mitted through the valve spindle to the valve disc. The disc seat in contact with the seaton the top of the valve nozzle forms the pressure boundary. The valve pressure bound-ary is maintained at the valve disc and nozzle seat that consists of circumferential,narrow metal surfaces. The valve seat is machined and optically lapped flat to maintaina tight seal when the valve is closed.

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Lifting Lever

Spring

Bellows

Adjusting Ring(upper ring)

Disc Seat

Nozzle Seat

Body

Inlet

Outlet

Nozzle Ring(lower ring)

Figure 4-14Crosby Safety Valve

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Lifting Lever

Spring

Bellows

Middle Ring

Disc Seat

Nozzle Seat

Body

Outlet

Upper Ring

Lower Ring

Figure 4-15Dresser Safety Valve

4-28



As the reactor coolant system (RCS) pressure at the valve inlet increases, it causes anincrease in the upward force acting on the wetted disc area. Therefore, the net forcekeeping the valve closed is reduced. When the inlet steam pressure reaches the valveopening pressure, the lifting force overcomes the spring force and increased steamleakage occurs across the disc to seat interface. This opening pressure is referred to asthe valve lift setpoint or lift set pressure. The leakage then expands into a “huddling”chamber beyond the valve disc to the nozzle seat interface formed by the disc enlargedarea and adjusting rings. The pressure builds rapidly in the huddle chamber and causesa sudden additional lifting force on the exposed disc/disc holder surfaces. This, in turn,causes the valve to lift and relieve system pressure. The valve opening is characterizedby a popping action as the steam rapidly expands through the valve. If the inlet pres-sure continues to rise, the flow force and increasing inlet pressure continue to lift thevalve to a full-lift position.

The valves are designed to achieve the full rated lift position at a steady state inletpressure of 3% above the valve popping pressure (as required by the ASME Code). Thevalue at which the valve achieves full rated lift, expressed as a percent of lift setpoint iscalled overpressure. At this pressure, the valve is designed to discharge rated steamflow. The system inlet pressure may continue to increase up to a maximum pressurethat is 10% above the valve lift set pressure, the system design upset limit as defined bySection III of the ASME Code.

When the overpressure transient has been relieved by the safety valves, the inlet pres-sure begins to decay. This allows the spring force to overcome the upward lifting forcesand results in the valve reseating. These valves are typically designed to re-close at apressure less than or equal to 5% below the valve set pressure. The difference betweenthe valve lift setpoint and closing pressure, expressed as a percentage of the lift setpressure, is called the valve blowdown.

NOTE: The following discussions are not intended to present all of the operational details ofthe Crosby and Dresser PRVs. The manufacturer’s technical manuals should be used for acomplete description of these valves.

4.2.1.2 Description and Operation of Crosby Pressurizer Safety Valves

Figure 4-16 shows a typical Crosby-style HB-BP safety valve in cross-section. The fol-lowing information covers the essential elements of the valve. Inside the body (1) ishoused the upper portion of the nozzle (2), the nozzle ring (3), the disc ring (7), theadjusting ring (12), the eductor (guide) (11), and the bellows assembly consisting of thebellows (8), a disc holder (5) and a disc ring (7). The disc insert is held in place in thedisc holder by an insert pint (10).

The eductor (guide) (11) and the bellows assembly and the bonnet adapter (15) areretained between the valve body (1) and the bonnet (18) by bonnet studs (38) and bon-net stud nuts (39).

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Housed in the bonnet (18) is the spring (19) and spring washers (20) carried by thespindle assembly (14), the lower end of which is positioned on the bushing (6) in thedisc holder (5). The spindle assembly also carries a piston (40).

The adjusting bolt (29) is locked in place by the adjusting bolt nut (30) at the top of thebonnet (18) within the cap (21).

Manual lifting means is provided by a lift lever (28).

21

29

2030

28

14

1840

15

8

1919

VENT

1919

38

39

11

12 65

10973

1

2

Figure 4-16Crosby Pressurizer Safety Valve, Style HB-BP

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The operation of the Crosby pressurizer valve is functionally the same as covered in thegeneral description. A few features are added to enhance the valve performance. Thedesign uses an eductor to minimize the effects of backpressure when the valve isopened. Fluid, after entering the huddle chamber, has 1) the direction reversed so as topass between the lower inside surface of the adjusting ring and the outer surface of thenozzle ring and 2) upward through an annular orifice between the disc ring OD andguide ring ID, then through a second annular orifice between the eductor OD andadjusting ring ID. The fluid finally enters the body bowl when exiting through holes inthe upper end of the guide ring. Flow through these passages controls the pressure inthe chamber external to the bellows and the effects of backpressure while the valve isopen. It also assists the spring force during disc closure (reseating).

Crosby changes valve disc and nozzle seating materials and seat designs as a functionof the valve installed condition. With the valve installed on 1) a loop seal (cold water atthe valve seat), a standard Crosby flat seat design is used with Stellite as the seatingmaterial and 2) when installed so the seating surfaces are exposed to steam, Crosby usesa standard or a flexi-disc seat design with a material selection that varies dependingupon the seat configuration.

4.2.1.3 Description and Operation of Dresser Pressurizer Safety Valves

A typical Dresser safety valve Series 31700 is shown in Figure 4-17. The valve consists ofa nozzle (1C) that is threaded into the valve body. The valve disc (5) is held in the closedposition against the nozzle seat by the force of a compressed helical spring (8A). Thespring force is applied to the disc from the spring through the spindle (7). This forcemaintains the disc/seat interface with the valve in the closed position.

The bellows (6A) is designed to reduce the effects of backpressure. The bellows can bedamaged if subjected to extreme conditions or severe cycling. Since the bellows per-forms such a necessary function in the valve, a balancing piston is required. Should thebellows fail, backpressure would enter the bellows internal chamber and act upon thepiston area thus negating the effects of backpressure on the valve set pressure andoperation. The piston accomplishes the same function as the bellows except for main-taining leak tightness between the valve outlet and bonnet. Flow will vent into the valvebonnet area through the clearance between the piston and floating washer (17), and thiswill be vented out of the valve bonnet. It is necessary that the valve bonnet vent connec-tion always be left open to atmospheric pressure.

When the inlet steam pressure reaches the lift set pressure, the vertical force counterbal-ances the spring force and a slight leakage of steam develops across the valve disc-to-seat interface and is directed into the huddle chamber. The huddle chamber beyond theseat to disc interface that is formed by the disc and disc holder enlarged area and theposition of the adjusting ring. Pressure builds up rapidly in the huddle chamber devel-oping an additional vertical lifting force on the disc and disc holder. This additionalforce in conjunction with the expansive characteristics of steam causes the valve to“pop” open to almost full-lift. The steam is directed through the secondary orifice and

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the adjusting ring flow gap. Steam momentum and the exposure of the larger area ofthe disc holder to steam pressure causes the valve to continue to full-lift until the liftstop comes in contact with the support plate. In addition, steam leaks through theclearance at the lower guide-to-disc holder interface generating an additional liftingforce on the upper portion of the disc holder. The static and dynamic force balancewhen the valve is open and flowing is shown in Figure 4-18 and described below.

Lifting Lever

Spring –– 8A

6A –– Bellows

Middle Ring

Disc Seat

Nozzle Seat

Body

Outlet

Upper Ring

Lower Ring

Spindle –– 7

Vent

Inlet1C

Valve Disc –– 5

Figure 4-17Dresser 31700 Safety Valve

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Nozzle-discseat interface

Section A-A

Huddle chamber

Secondary orifice

Lower adjusting ringpoint diameter

Lift stop

Support plate

Upper guide discholder interface

Disc holder

Upper adjusting ring

Lower guide-discholder interface

Valve body bowl

Middle adjusting ring

Valve body bowl

Lower adjusting ring

Nozzle

Guidelower

portholes

Guideupper

portholes

Figure 4-18Dresser Detail Showing Force Balance

A vertical upward force (F1) results from the steam pressure against the disc. A verticalupward force (F2) results in pressure acting on the increase in the effective area of thehuddle chamber. This force is controlled by the position of the lower and middle adjust-ing rings directly affecting the function of the huddle chamber.

A vertical downward force (F3) due to the spring force is defined by the lift set pressuretimes the seat area.

A vertical downward force (F4) is due to steam leaking through the clearances betweenthe guide-to-disc holder interface, the disc-to-disc holder interface, and the bellows discnut-to-disc holder thread interface and the upper compensator ports.

A vertical upward force (F5) is created due to steam passing through the lower guide-to-disc holder interface and expanding into the chamber under the upper portion of the discholder. Steam flow out of this chamber is affected by the position of the upper adjustingring body pressures near the lower port holes in the guide and also by the upper guide todisc holder interface.

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When the inlet pressure decays, the upward pressures (F1, F2, F5) decrease allowing thespring force (F3) plus the pressure at the top of the disc holder (F4) to reseat the valve.

4.2.1.4 Design Comparison - Crosby and Dresser Safety Valve

The following is a brief comparison of a few of the more important features of theCrosby and Dresser safety valves. This comparison should aid in understanding thevarious aspects of each valve design. The first difference between the Crosby andDresser safety valves is the design features that control the backpressure above thevalve disc. Crosby valves control main disc backpressure by an educator design. Leak-age past the disc ring is directed by the educator through ports in the guide ring. In theDresser valves, valve disc backpressure is controlled by the upper adjusting ring. Ad-justing the upper ring up or down closes or opens up flow paths in the disc guide.Blocking the holes traps fluid that leaks past the disc holder. Exposing the holes allowsleakage to escape into the valve body. The guide also has upper portholes that controlbackpressure into and out of the chamber above the disc holder. Upper ring position isselected and fixed by Dresser for all its valves. Crosby valves control main discbackpressure by an eductor design. Leakage past the disc ring is directed by the eductorthrough ports in the guide ring.

The Crosby and Dresser safety valves have different seat designs:

• The Crosby seat designs were discussed in Section 4.2.1.2 and, as stated previously,vary the seat configuration and material based on the installation. On some earlierdesigned nuclear plants, valve seat leakage was experienced. Loop seals were in-stalled to eliminate these seat leakage problems. The leakage was due to valve seatsbeing exposed to entrained hydrogen gas in the pressurizer and high ambient tem-peratures that affected valve set pressures not compensated for during testing. Thecombination of Stellite seating materials on a cool-water interface eliminated the seatleak problem. Further improvement in valve seat designs and seat materials as wellas a review of the valves installed conditions such as ambient temperatures anddischarge piping loads helped resolve seat leakage problems when the valve wasinstalled without a loop seal.

• Dresser valve seats are flat and use the thermodisc design on the disc insert. TheDresser valves are typically installed in plants without loop seals leaving the seatsexposed to steam instead of subcooled water. Thermodisc design permits the discseat, as in the Crosby flexi-disc, to give temperature stability and flexibility thatenhance seat tightness as the inlet pressure approaches the valve set pressure.

The Crosby and Dresser valves both have a bellows attached to the disc or disc assem-bly, exposed externally to the outlet pressure, and internally exposed to the atmospherepressure in the bonnet. The purpose of the bellows is to minimize the effect ofbackpressure. Without a bellows, backpressure on the disc would cause a downwardforce in addition to the spring force. This higher force would cause an increase in thevalve opening pressure. Both manufacturers include a piston as a backup to the bel-lows, an ASME Section III Code design requirement for these valves. In the event of abellows failure, the piston provides a counterbalancing lifting force if pressure ispresent in the bellows area.

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Both valve manufacturers supply one basic valve design for PWR plant applications.They also supply a range of valve sizes in order to meet the rated relieving capacityrequirements specified by the Nuclear Supply System manufacturers. These size incre-ments vary as a function of both valve inlet size and by the valve orifice designationslisted in Table 4 - 1. Each orifice has a design flow area with a certified flow coefficientand a rated relieving capacity at the certified overpressure that is the minimum flowarea through the valve when it is fully open.

Table 4-1PWR Safety Valve Sizes and Flow Rates

Valve Designation Orifice Size

(in.2)

Rated Capacity at 3%Overpressure

(lbs/hr Saturated Steam@ 2575 psia)*

Dresser 31739A 3 2.55 298,000

Dresser 31749A 4 3.98 504,103

Dresser 31759A 5 3.34 423,467

Dresser 31709NA N 4.34 508,000

Crosby 3K6 K 1.84 212,000

Crosby 3K26 K2 2.54 295,000

Crosby 6M16 M1 2.99 347,000

Crosby 6M6 M 2.64 420,000

Crosby 6N8 N 4.38 505,000

Target Rock 69C -- 3.51 345,000

*Note: Rated capacity can vary based on year of valve manufacture due to the use of thecorrection factor in ASME Section III, Subsection NB, Article NB70000 for valveswith set pressures above 1500 psig.

4.2.1.5 Description and Operation of Target Rock Pressurizer Pilot-Operated Valve

The Target Rock pilot-operated PRVs used for PWR application has two main assem-blies: a pilot valve section and a main valve section. These two sections are constructedas one unit to provide a self-actuated relief valve. The pilot valve section is the pressuresensing and control element, and the main valve is actuated by the system fluid. Themain valve provides the pressure relief function. The pilot section is a low flow pressuresensing element that actuates the main valve. Pilot incorporates a machined bellowsthat acts as a combination piston, spring, and hermetic seal in the pilot valve. As shownin Figures 4-19(a) and (b), the top of the bellows is connected to the pilot valve discthrough a stem and disc yoke. Between these components there is an adjustable clear-ance or abutment gap. The pilot valve works as follows:

1. During assembly, the bellows is extended a small amount to provide a pre-loadforce on the pilot valve disc. This seals the disc tightly and prevents reverse leakage.

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2. During operation, as system pressure increases, the pre-load force is reduced tozero. The pilot valve disc is held closed by the internal pressure acting over the pilotvalve seat area. This seating force increases with increased system pressure.

3. As system pressure increases, the expanding bellows reduces the abutment gapbetween the stem and disc yoke. When the stem contacts the yoke, a further pressureincrease will reduce the net pilot seating force to zero and the disc lifts from its seat.

4. At a higher pressure, the pilot valve starts to open and the hydraulic seating force iseliminated, resulting in a net increase in force that opens the pilot valve.

The main valve operates as follows:

1. In the normally closed position, the main valve disc is seated by the combined forcesexerted by the main valve pre-load spring and by the system internal pressureacting over the area of the main valve disc.

2. When the system pressure increases to the pilot valve (lift) set pressure, the pilotvalve opens. This admits the fluid pressure to the area above the main valve piston.This flow creates a differential pressure across the main valve piston in a directionthat tends to open the valve. The main valve piston is sized so that the resultantopening force is greater than the combined pre-load and hydraulic seating forces.Therefore, opening the pilot opens the main valve.

3. Similar to the pilot valve, when the main valve disc starts to open, the hydraulicseating force is reduced. This causes a significant increase in opening force and thecharacteristic full opening or popping sound.

4. When the pressure has reduced until the pilot valve closes, leakage of system fluidpast the main valve piston decreases the pressure over the piston. This eliminatesthe hydraulic opening force and permits the pre-load spring to close the valve. Onceclosed, this additional hydraulic seating force due to system pressure acting on themain valve disc seats the main valve.

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(a)

Inlet

Outlet

Main valvedisc (open)

Pilot valvedisc (open)

Abutment gap(closed)

Inlet

Outlet

Main valvedisc (closed)

Main valvepreload spring

Main valve piston

Abutment Gap

Pilot ValveDisc closed

Bellows

Pilot preloadsetpoint adjustmentspring

Yoke portion ofpilot valve disc

Pilot sensing port

(b)

High-pressure fluid

High-pressure fluid

Figure 4-19(a-b)Target Rock Pilot-Operated Valve (Open) (a) and (Closed) (b)

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In addition to the flow over the main disc and the pilot valve, there are other differencesworth noting for the pilot-operated design compared with the spring-loaded design. TheTarget Rock pilot-operated valve does not contain adjustment rings. Valve adjustmentsare machined into the pilot assembly by the valve manufacturer, not adjusted later.

The main disc does not have a secondary pressure chamber exposed to system steampressure and the resulting additional pressure forces. It is important to note that pilotvalves are a sequential opening device and therefore as in any sequential, step function,opening device there is a delay time (see Glossary, Appendix F) in the opening of thevalve that causes release of inlet pressure. This opening time can vary as a function ofsystem pressure rise rate and system fluid/condition. This is unlike the opening of aself-actuated safety/safety relief/relief valve which opens in direct response to (inletstatic) system pressure. Opening times of about 200 milliseconds are typical comparedto spring-loaded valves with 10 to 20 milliseconds opening times.

4.2.1.6 Summary

PWRs have one or more safety valves mounted on the pressurizer to protect the plantfrom potential overpressurization transients. Although other system pressure controlequipment is also available, the self-actuated safety valves are used as the last resort ofoverpressure protection as required by the ASME Code Section III Subsection NB.

Typical PWR plants have two to four safety valves designed to open automatically at2500 psia. They pass steam flow rates from 210,000 to 600,000 lbs/hr. per valve and re-close automatically at pressures about 5% below the valve opening pressure.

4.2.2 BWR Main Steam Service PRVs

The BWR main steam system uses PRVs to protect the reactor primary system fromoverpressure. The valves are also used to depressurize the reactor’s primary system, ifnecessary, when the primary system pressure is below the PRV set pressure.

These pressure relief designs may be a safety valve that is self-actuated by the system inletstatic pressure or a pilot-operated valve that may have a direct acting or indirect actingpilot that self-actuates by the system static pressure to open the main valve disc. Bothvalve designs incorporate a secondary system to open the valve. The secondary systemrequires an external power source, electromagnetic or electropneumatic, that, in turn,mechanically causes the valve to open and relieve system pressure. In this mode of opera-tion, the PRD stays open until the external power source has been de-energized. PRVshaving this type of operating capability are generally categorized as dual-function PRVs.

This section reviews typical manufacturer designs of BWR PRVs.

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4.2.2.1 General Description of BWR Safety Relief Valves

There are two types of self-actuated, spring-loaded, dual-function safety valve designscurrently used on BWRs. These valves are manufactured by Crosby and Dikkers. Thisvalve design is also described as safety valves with an auxiliary actuating device.

Each of these manufacturers’ valve designs will 1) operate by self actuation—open at apreset value upon an inlet static pressure rise or 2) open in the relief mode of operationwhen an external electrical signal is applied to a solenoid that opens and permits pres-surization of a pneumatic cylinder that mechanically opens the valve.

In many plant applications, these PRVs are automatically opened in the relief mode ofoperation by a pressure signal initiated by a pressure transducer or transmitter locatedin the reactor vessel. Using a pressure value corresponding to a preset pressure value ofa control device, the valve is mechanically actuated. In this relief mode, the valve can beopened by the plant operator transmitting an electrical signal as required by plantoperating procedures.

Two other types of dual-function, pilot-operated PRVs are also used in some BWRs.They are Target Rock’s two-stage and three-stage PRVs. The pilot-operated valve de-signs of these PRVs require the pilot section to open before the main valve.

4.2.2.2 Crosby Safety/Relief Valve

The Crosby safety relief valve as shown in Figure 4-20a automatically opens whenincreasing static inlet steam pressure acting as the disc exerts an upward force sufficientto overcome the spring set load.

When the disc begins to lift, a small amount of steam flows past the nozzle and disc seat-ing surfaces and is deflected through an angle created by the nozzle ring and disc ring.The steam acts upward on the enlarged exposed area of the disc ring and increases theupward force causing an incremental change in the upward force that overcompensatesthe spring force and causes the disc to lift. As the disc lift increases, the flow increases andthe total upward-generated force pops the valve open to the full-lift position. The inletpressure value at which the pop action occurs is termed the “popping pressure” andcorresponds to the set pressure value stamped on the nameplate attached to the valve.

Figure 4-20b is a cross section of the valve internals when the valve is opened anddischarging. Note that the primary flow reverses direction to flow between the nozzlering and the adjusting ring. The secondary flow (eductor flow) is upward and passesthrough a series of annular orifices, A and B, that control the pressure developed inchambers C and D. Steam flows through slots in the eductor at H and into chambers Cand D. Steam that bypasses the eductor exhausts into the valve body cavity throughopenings in the adjusting ring. Pressure in chambers C and D and opening E is greaterthan the body discharge cavity pressure.

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4-40



As the inlet pressure decays to a value below the actual lift set pressure, the upwardforce on the lower face of the disc and the disc ring decreases and the valve disc beginsto close. The closing action, produced by the difference between the upward forces andthe downward spring force, is also assisted by a downward force produced by thepressures in chambers C and D. Closure (blowdown) for the valve is controlled byadjusting the position of the adjusting and nozzle rings. Their set locations are deter-mined by manufacturer tests. Their position controls the net upward force produced bythe steam on the lower face of the disc insert and disc ring.

Proper adjustment will result in a sharp pop at open and a precise reseat pressureblowdown. Blowdown can be varied within the design limitations for a given serviceapplication. The characteristic blowdown setting established by the manufacturer forBWR PRVs ranges between 2 to 11%.

To assure stable valve performance and mitigate the effects of backpressure in the valvebody discharge cavity, a bellows as shown in Figures 4-20(a) and (b) is used. The bel-lows, sized to be approximately equivalent to the valve seat area, balances the down-ward force produced by static flow-induced backpressure. A balancing piston is alsoprovided as a backup to the bellows in case the bellows fails.

An electropneumatic actuator assembly and associated linkage is attached to the valveto provide an independent and separate means to open the valve when the system inletsteam pressure is less than the valve’s spring set pressure value. This method of operat-ing the valve is referred to as the relief mode. The auxiliary actuating device permitsopening the valve to:

• Depressurize the reactor under accident conditions.

• Control reactor operating pressure within designated values. This function is actu-ated by an external logic system controlled by redundant pressure sensors thatmonitor reactor steam dome pressure.

The electropneumatic actuator assembly consists of a piston-type pneumatic cylinderand two or three solenoid and air valve assemblies (for redundancy) attached to thecylinder manifold. The actuator assembly is interconnected to the valve using a leverand lifting mechanism. When the solenoid is energized; the air valve is stroked intoposition permitting air pressure to enter the area below the piston in the cylinder. Pres-sure in the cylinder then pushes the piston upward, which in turn actuates the lever andlifting mechanism. This, in turn, mechanically moves the spindle upward causing thedisc insert to lift from the nozzle seat.

When the solenoid is de-energized, the air valve returns to the exhaust position. Thepressure under the piston in the cylinder exhausts to the atmosphere through the ex-haust porting. As the cylinder pressure decreases, the valve spring causes the disc insertto reestablish nozzle seat contact, and the valve closes.

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4.2.2.3 Dikkers Safety Relief Valve

The Dikkers PRV as shown in Figure 4-21(a) operates on the same principle as theCrosby PRV. One key difference is that in the safety mode of operation, the effect of theflow-induced backpressure that tends to close the valve is controlled by venting thepressure in the body bowl cavity behind the disc and piston as shown in Figure 4-21(b).This type of backpressure control scheme eliminates the need for a bellows. However, itincorporates a graphite-type packing ring to minimize backpressure leakage to theatmosphere while ensuring minimal frictional effects on the valve lift setpoint.

For the Dikkers valves, the spring force is provided through the use of Belleville springwashers instead of a conventional spring.

In the relief mode, the Dikkers PRV operates in the same manner as the Crosby PRVwhich is through the use of an actuator assembly.

4.2.2.4 Target Rock Pilot-Operated Relief Valves

The second type of PRV used in BWR plants is the pilot-operated valve. These valves,installed in several BWR plants, are either two-stage or three-stage designs. Figures 4-22(a) and (b) are cross-sectional schematics of a two-stage Target Rock pilot-operated reliefvalve. The operational characteristics of the valve are different from those of the directspring actuated valves, but similar to the Target Rock pilot-operated relief valve used forPWR applications.

4.2.2.4.1 Target Rock Two-Stage, Pilot-Operated Relief Valve

The Target Rock two-stage, pilot-operated relief valve consists of two principle assem-blies: a pilot stage assembly and the main stage assembly as shown in Figures 4-22 (a) and(b). These two assemblies are directly coupled to provide the dual-function relief opera-tion modes as in the Crosby and Dikkers safety/relief valve. The pilot assembly is thepressure sensing and control element, and the main assembly is actuated by the pilotvalve and provides overpressure protection and pressure relief. In the self-actuationmode, the pilot assembly (lift) set pressure vents the main piston chamber permitting themain disc to fully open. This results in system depressurization due to inlet fluid dis-charge. Operation of the pilot assembly and main assembly is described below.

4-42



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4-43



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4-44



Self-Actuation Mode:

The pilot stage operates as follows:

1. The pilot assembly consists of two low flow pressure sensing elements. The spring-loaded pilot disc senses the (lift) set pressure, and the pressure loaded stabilizer discsenses the reseat pressure. Using the pilot rod, spring force is applied to the pilotdisc. The adjustment of the spring creates a pre-load force to establish the (lift) setpressure value of the valve.

2. When system pressure increases at the valve inlet and reaches the adjusted (lift) setpressure, the net downward force acting on the pilot disc is reduced to zero, causingthe pilot disc to lift from the seat. Pilot disc lift results in the depressurization of themain piston chamber volume through the pilot stage discharge port. Initial depres-surization of the main piston chamber creates a differential pressure across thestabilizer disc in an upward direction, causing the stabilizer disc to seat. The systempressure, which acts on the stabilizer disc via the internal porting, maintains thepilot disc in the open position. This permits the main piston chamber to vent untilthe required differential pressure across the main piston is achieved. The main discthen opens to permit flow from the system inlet side to be relieved. When the systempressure has decreased to the valve reseat pressure, the pressure-sensing stabilizerdisc unseats. This permits the pilot disc to reseat causing the main piston chamber torepressurize and close the main stage.

3. The main stage assembly of the Target Rock PRV is a reverse pressure seated-systemfluid actuated angle globe valve. Actuation of the main valve disc permits the dis-charge of fluid from the system at rated capacity and provides the system with anoverpressure protection pressure relief function. The major components of the mainstage are the valve body, main disc/piston, and the main spring.

4. In the closed position, the main (stage) disc is seated by the combined forces of themain spring and the system internal pressure acting over the area of the main disc.In the closed position, the static pressures in the valve inlet nozzle and in the cham-ber over the main stage piston are equal. This pressure equalization is made possibleby internal passages.

5. When the system pressure at the valve inlet increases to the valve (lift) set pressure,the pilot disc opens and vents the main piston chamber via internal porting to thepilot stage discharge port and to the discharge side of the valve. As discussed previ-ously, this venting creates a differential pressure across the main piston in a direc-tion that tends to open the main disc. The main piston is sized such that the netopening force is greater than the combination of the main spring pre-load and sys-tem pressure forces acting on the main disc. Once the main disc starts to open, theseating force is rapidly reduced, causing the main disc to fully open with the charac-teristic pop action.

6. Once the system pressure at the valve inlet is reduced to the reseat pressure, thepilot disc reseats. This permits the repressurization of the main piston chamber. Theflow of system fluid through the main piston ring gap and stabilizer disc seatingarea repressurizes the chamber over the piston. The repressurization of the piston

4-45



chamber equalizes system pressure forces and permits the main spring and flowforces to close the main valve disc.

Relief-Actuation Mode:

A diaphragm type pneumatic actuator is attached to the pilot stage assembly to provideoperation of the valve at system pressures ranging from 50 psig to the valve set pres-sure. It is actuated by means of a solenoid control valve that admits air to the air opera-tor piston chamber and strokes the air operator stem upward. This action compressesthe spring and lifts the pilot rod to permit the pilot disc to lift to its open position. Themain stage then opens as previously discussed. De-energizing the solenoid vents thediaphragm chamber, causing the air operator stem to return to its closed position. Thepilot stage then reseats if the system pressure is at or below the reseat pressure. Whenthe pilot stage reseats, it causes the main stage to reseat as previously discussed.

4.2.2.4.2 Target Rock Three-Stage Safety Relief Valve

The Target Rock three-stage, pilot-operated PRV consists of two principal assemblies: atwo-stage pilot valve section and the main valve section as shown in Figure 4-23. Thetwo sections are coupled to provide a self-actuated PRV. The pilot valve section is thepressure-sensing and control element, and the main valve provides overpressure pro-tection pressure relief. Self-actuation of the pilot valve at the valve (lift) set pressurevents the main piston chamber, permitting the main valve disc to fully open allowingfluid pressure from the valve inlet to be relieved.

Self-Actuation Mode:

1. The pilot valve section of the Target Rock three-stage PRV is a low flow pressuresensing and control element that actuates the main valve. A component in the pilotvalve is the bellows that acts as a combination piston, spring and seal. As shown inFigure 4-23, the top of the bellows is connected to the pilot stage disc through thestem and disc yoke. There is an adjustable clearance, or abutment gap at this connec-tion point.

2. During assembly, the bellows is slightly extended to provide a pre-load force on thepilot stage disc, sealing the disc tightly and preventing leakage at low system pres-sure or high backpressure.

3. As the system pressure increases, the pre-load force is reduced to zero, and the pilotstage disc is held closed by the internal pressure acting over the pilot stage seat area.As system pressure increases, the bellows expansion reduces the abutment gap be-tween the stem and disc yoke. When the stem contacts the yoke, an additional pres-sure increase reduces the net pilot seating force to zero and lifts the disc from its seat.

4. When the pilot stage starts to open, the fluid seating force is reduced. This results ina net increase in the force that tends to extend the bellows. This increase in net forceproduces a pop action during the pilot opening. Opening of the pilot admits fluid tothe operating piston of the second stage, causing it to open. Then the opening of themain valve (third stage) follows.

4-46



BellowsBonnetBellows Leakage

Alarm Port

Preload Spacer

Pilot Stem

Pilot Preload and Set-Point

Adjustment Spring

Yoke Portionof Valve Disc

Pilot Sensing Port

Main ValvePreload Spring

Main Valve Piston

Main ValvePiston Orifice

Main Valve Disc(Closed)

Outlet

High Pressure Fluid

Inlet(System Pressure)

Second Stage Disc (closed)

Second Stage Preload Spring

Second Stage Piston

Second Stage Piston Orifice

Pilot Disc (closed)

Remote Air ActuatorAbutment Gap

Figure 4-23Target Rock Three-Stage Pilot-Operated Valve

The main valve (third-stage) operation is as follows:

1. The main valve section of the Target Rock PRV is a reverse-seated, hydraulically-actuated, angle-globe valve. Actuation of the main valve permits the discharge ofinlet fluid to provide overpressure protection to the system. The parts of the mainvalve are the valve body, disc/piston assembly and main spring.

2. In the normally closed position, the main valve disc is seated by the combined forcesof the system pressure acting over the area of the main valve disc and the mainvalve spring. In the closed position, the static pressures are equal at the valve inletand in the chamber over the main valve piston. This pressure equalization is madepossible by leakage past the piston, via the piston ring gap, piston orifice, and inter-nal drain and vent grooves.

4-47



3. When the system pressure increases at the valve inlet to the pilot (lift) set pressure,the pilot and second stage of the pilot valve open. This action vents the chamberover the main valve piston to the outlet side of the valve. This venting creates adifferential pressure across the main valve piston in a direction that causes it toopen. The main valve piston is sized such that the net opening force is greater thanthe combined spring pre-load and fluid seating forces.

4. When the main valve disc starts to open, the fluid seating force is reduced, creating asignificant increase in opening force that causes the disc to fully open with a popaction.

5. When the inlet fluid pressure has been sufficiently reduced, the pilot reseats. Thesecond stage also reseats after depressurization of the second-stage piston chamber.This is accomplished by leakage past the piston rings and piston orifice. The leakageof system fluid past the main valve piston repressurizes the chamber over the pistonand permits the main spring and fluid pressure to force close the main valve disc.

Relief-Actuation Mode:

A diaphragm-type pneumatic operator is attached to the pilot valve assembly to pro-vide operation of the valve at other than the self-actuated (lift) set pressure. It is actu-ated by means of a solenoid control valve that admits air to the air operator pistonchamber and also strokes the air plunger which strokes the second-stage disc. The mainvalve disc then opens as described above. De-energizing the solenoid vents the airoperator and permits the second stage disc to close. The main valve then reseats asdescribed above.

4.2.3 PWR Pressurizer Power-Operated Relief Valves (PORVs)

4.2.3.1 Application and Typical Types of PORVs

The primary system components in PWRs are protected against overpressure by PORVsand self-actuated, spring-loaded safety valves. The PRVs are designed to open and relievethe system pressure during a transient that results in pressure surges above the specifiedlimits. The PORVs are actuated by an external power source that is either electromagneticor electropneumatic. This external power source acts directly on the main valve (direct-acting) or on a pilot valve (pilot-operated) that causes the main valve to open.

PORVs used in PWR plants can be divided into two major categories: direct-acting andpilot-operated. In the direct-acting valves, the external power source acts directly on themain valve causing the plug or disc to be lifted off from the seat. The direct-actingvalves usually contain a pneumatic operator. The pilot-operated valves contain a sec-ondary or pilot valve that is opened by the external power source through a solenoid orelectromagnet. Opening of the pilot valve reduces the pressure behind the main disc.This causes the main disc to lift from the seat and results in the valve relieving systempressure. Direct-acting valves include those manufactured by Control Components andCopes-Vulcan. Pilot-operated valves include those manufactured by Crosby, Dresserand Garrett (serviced by Crosby). The Garrett valve employs a three-way pilot system

4-48



(similar to a pilot valve) to reduce the pressure on the main valve disc (plug). An excep-tion to the above two categories is the internally piloted, solenoid-operated relief valvemanufactured by Target Rock. This Target Rock valve contains an internal pilot discthat is lifted by a solenoid. This causes the pressure behind the main disc to reduce andthe disk to be hydraulically lifted off the main seat.

4.2.3.2 Description of Manufacturer’s Relief Valves

Each type of PORV mentioned above is described below.

Typically the Crosby PORVs used in PWRs are model HPV-SN pilot-operated valves asshown in Figure 4-24. They are externally actuated by an electrical power source.

Inside the main valve body (1) are housed the lower portion of the nozzle disc (4) and theguide and the spring (6). The pilot valve body (2) is welded to the main valve body (1).The pilot valve (nozzle) is retained between the pilot valve body and the bonnet by thebonnet studs (12) and nuts. The disc (14), spring (21), spring washer and retaining ring arehoused in the nozzle and bonnet. Also contained within the bonnet by the bellows topadapter is the bellows (17) and the disc actuator (19). The solenoid bracket (28), solenoid(35) and solenoid cover (41) are attached to the main valve body by the bracket studs (27)and nuts (26). The adjusting bolt (31) is threaded into the lever (33) and held in place bythe adjusting bolt lock nut (32). The link (29) connects the lever (33) and solenoid (35).

Nozzle

Disc

Spring

Body

Inlet

Outlet

Pilot Valve Disc

Pilot ValveDisc Aculator

Solenoid

14

19

21 2317

25

29

26 27

35

41

31323312

2

1

6

4

5

Figure 4-24Crosby (Model HPV-SN) PORV

4-49



Under normal operating conditions, the inlet port A, cavities B and C, and the pilot valveconnecting cavity D are at the same fluid pressure. Since the pressure in cavity C is greaterthan the pressure in the discharge port E, the main valve disc seats against the nozzle seat.The pilot valve disc seats against the nozzle (pilot valve) seat since the pressure in theconnecting cavity D is greater than the pressure in the pilot valve discharge port F.

When the solenoid is energized, the solenoid plunger actuates the lever (solenoid),causing the adjusting bolt to strike the top end of the disc actuator (pilot valve). Thisaction unseats the pilot valve disc and allows steam to pass through the vent holes inthe nozzle (pilot valve) to the pilot valve discharge port F. When the pilot valve opens,pressure in cavity C is reduced and the greater pressure in cavity B causes the mainvalve disc to open. When the solenoid is de-energized, the solenoid plunger returns tothe original free position. The pilot valve closes, causing pressure to build up again incavities C and D, thereby closing the main valve disc.

4.2.3.3 Dresser PORVs

The PORVs supplied by Dresser are pilot-operated, electrical push-action solenoid(“Electromatic”) and electromagnetic PRVs externally actuated by an electrical powersource.

The Dresser Electromatic relief valve consists of a body assembly, pilot valve, and anelectromagnetic solenoid assembly. It is normally installed in the vertical position asshown in Figure 4-25. When the valve is de-energized, system inlet pressure is sensed inchamber areas A, B, C, D and F. The disc is held closed by the disc spring and the steampressure in chamber C. The pilot disc is held closed by the pilot spring and the steampressure in chamber F. The steam pressure assists in seating both the disc and the pilotdisc, referred to as a reverse seated design.

When the solenoid is energized, the solenoid plunger moves downward and strikes theoperating lever with sufficient force to cause downward motion of the pilot disc stemcompressing the pilot spring and opening the pilot disc. As the pilot disc moves off itsseated position, steam in chamber F is released across the seat and exhausted throughthe pilot valve vent. This pilot action causes depressurization of chambers C and E andresults in a pressure differential of sufficient magnitude across chambers B and C toopen the disc from its seated position. This permits steam to flow from the inlet to theoutlet side of the valve at its rated flow capacity. Portings D, E, and F, and the pilotvalve vent, G, are sized to permit the steam pressure in chamber C to be exhaustedfaster than it is being pressurized. The steam flow exhausting through the pilot valvevent is small compared with flow through the valve. Therefore, as long as the solenoidis energized, the valve will remain open.

When the solenoid is de-energized, the pilot disc is seated by the pilot spring and thepressure in chamber F shuts off flow to the pilot valve vent. This permits chambers C, E,and F to be pressurized through chamber D and by leakage past the piston rings and discguide. This, in turn, permits the disc spring to overcome the unbalanced forces acrosschambers B and C and seat the disc. After the disc is seated, pressures in chambers B, C,D, E, and F, equalize to the inlet pressure value at chamber A as described above.

4-50



Figure 4-25Dresser Electromatic Relief Valve (Model 1525VX)

4.2.3.4 Control Components PORV

The PORV made by Control Components is a globe-style body shown in Figure 4-26.The valve operator is a double-acting piston air-operated cylinder. Two springs areused above the operator piston to close the valve in the event of air loss. The operator iscontrolled by two three-way solenoid valves. The main internal components of thevalve are the plug, seat ring, and disc stack. The disc stack assembly consists of manydiscs layered together. Flow through the valve is restricted because the disc stack variesthe number of turns and the area of flow passages on the individual discs. As the valveopens, the plug lifts off the seat and travels up the disc stack bore. Fluid then enters thevalve body and flows from the outside of the disc stack into the disc stack bore area,past the seat ring, and out of the valve discharge.

4-51



Plug

Seat Ring

Disc Stack As

Spring

Figure 4-26Control Components PORV

4.2.3.5 Copes-Vulcan PORV

All Copes-Vulcan PORVs have globe-style valve bodies, and the actuator uses a reverse-acting diaphragm operator. Figure 4-27 shows the components of the Copes-Vulcanvalve mode. The valve consists of a 3-inch cast or forged straight-through valve body,and all valves have a bolted style body-bonnet joint. This joint has a mechanical center-ing feature that uses a metal-to-metal shoulder to control gasket deformation. Thegaskets are enclosed in the valve body and compressed as required by the design.

In the reverse-acting operator, a large compression spring provides the seating force forthe stem and plug. Air pressure is used to load the diaphragm chamber which over-comes the spring force and strokes the valve.

The trim supplied for all Copes-Vulcan PORVs is of the unbalanced, single-seat, andplug-throttling design. This trim modulates with a plug that has a contour on the lowerend, and its motion varies the annular flow clearance between the plug and cage.

4-52



Actuator

Spring

Stem

Cage Spacer

Cage

Flow

Plug

Figure 4-27Copes-Vulcan PORV

The cage is a cylindrical spool piece surrounding the plug. It has flow ports that uni-formly distribute the flow around the plug. The cage also contains the seat joint. Thiscombination of cage, cage spacer, and plug provides the following principal advantages:

• Stable throttling at any pressure drop

• Reduction in the side load and friction due to the uniform flow distribution throughthe ports

• Longer seat life by eliminating chatter at low lifts

• Ease of maintenance due to quick change design

4.2.3.6 Target Rock

The Target Rock PORV model is a direct-acting, solenoid-operated globe valve that usesan internal pilot within the main disc as shown in Figure 4-28. This valve’s main disc ispressure-seated by the fluid on the upstream side of the valve. A pilot disc is containedwithin the main disc. Energizing the solenoid coil lifts the pilot disc off the seat in themain disc and drops the pressure from chamber above the main disc. When the pres-sure in this chamber drops to approximately half the inlet (upstream) pressure, themain disc is lifted from its seat.

4-53



When the solenoid is de-energized, the pilot disc is reseated in the main disc. Thisallows the upstream pressure to enter the chamber above the main disc. The buildup ofpressure in this chamber recloses the main disc.

A push rod and magnet are attached via several connecting members to the main disc.When the main disc moves, the magnet is moved a distance equal to the main disc lift.The magnet’s motion is detected by reed switches that provide a positive indication ofmain disc position. For system checkouts, the main disc with the attached magnet can bemagnetically opened and closed. In the absence of a pressure differential across the valve,the solenoid force is sufficient to lift the main disc against the force of its return spring.

The fluid force lifting the main disc is aided by a solenoid force which, acting on themovable core, contributes a sufficient force to lift the main disc against the force of itsreturn spring.

4.2.3.7 Crosby (Garrett) Pneumatic Systems1

Crosby (Garrett) PORVs used in PWRs are pilot-operated, solenoid-controlled reliefvalves. The two basic designs, shown in Figures 4-29 and 4-30, are similar in operationand differ mainly in the configuration of the body.

The simplified schematic in Figure 4-31 shows the basic components of these valves,with the solenoid de-energized and the valve in the closed position. Inlet pressure flowsthrough the valve inlet and is ported through the supply seat to the actuator headchamber of the valve. The inlet pressure is also ported below the piston and through thecage holes to surround the plug. The forces holding the valve closed include the pres-sure in the actuator head chamber acting on the entire piston area and the actuatorspring load. (Note that the actuator spring load is primarily used to keep the valveclosed at low inlet pressures.) Inlet pressure also acts on the annular area of the plugoutside the seat diameter in a direction that opens the valve. Since this total annulararea to open the valve is less than the total piston area, the closing force is higher andthe plug is held down against the seat.

When the solenoid is energized, the magnetic force acts on the solenoid armature tomove the valve seat ball from the vent seat as shown in Figure 4-31 to the oppositesupply seat. This seals off inlet pressure to the actuator head chamber. The actuatorhead pressure is vented to discharge through the vent seat. With the actuator headchamber vented to discharge, inlet pressure acting on the annular piston and plug areais sufficient to overcome the actuator chamber pressure. The plug then moves off thevalve seat in the direction that opens the valve.

As the valve opens, pressure inside the cage builds up below the portion of the plugexposed to discharge pressure, causing the plug to continue to move to the full-liftposition.

1 This product was originally manufactured by Garrett Pneumatic Systems. Presently the installed base ismanufactured by Garrett and any new product is manufactured by Crosby Valve and Gage Company.

4-54



When the solenoid is de-energized, the ball moves back to the vent seat and seals theflow path to discharge. The actuator head chamber is thus repressurized with inletpressure through the supply seat and the plug moves to make contact with the valveseat and then closes. The closing forces of the plug consist of the inlet pressure acting inthe actuator head chamber.

Flow

Pilot Seat

Main Disc

Plug

Solenoid Assembly

Pilot Disc

Figure 4-28Target Rock PORV

4-55



CageSeal

Body

Plug

Solenoid

Figure 4-29Crosby (Garrett), Right Angle PORV

Solenoid

Cage

Seat

Body

Plug

Figure 4-30Crosby (Garrett), Straight Through PORV

4-56



Three-way solenoid Actuatorheadchamber

Actuatorspring

Piston area

Inlet flow

Valve seat

Dischargeflow

PlugSupplyseal

Solenoidspring Vent

seal

Figure 4-31Crosby (Garrett), PORV Schematic Diagram

4.2.4 PWR Secondary System Main Steam Safety Valves (MSSVs)

The secondary steam system for PWR power plants is protected from overpressure byself-actuated safety valves. Typically, a PWR secondary main steam system will have aquantity of 12 to 16 main steam self-actuated safety valves installed on the main steamheader. These valves may vary in inlet size depending upon plant size. Larger plantsgenerally use a 6-inch nominal pipe size inlet (6- or 10-inch single or dual outlets) with aset pressure ranging from 1000 to 1350 psig and with rated capacities of approximately500,000 lbs/hr. saturated steam. The valves are manufactured to the requirements ofASME Section III, Subsection NC (Class 2) and Article NC7000.

These safety valves, typically manufactured by Crosby or Dresser, are shown in Figures4-32 and 4-33. A general description of these PRVs follows.

Crosby PWR Main Steam Safety Valve

The Crosby Style HA-FN safety valve is shown in Figure 4-32(a) and (b). This figureshows the safety valve assembly in cross-section and covers the essential elements ofthe valve.

Housed inside the body (1) is the upper portion of the nozzle (that has a flat seat) (2),nozzle ring (3), guide ring (10) and guide (8A). The disc insert (6) (which has a flat seat)is held in place in the disc holder (5A) by the disc insert pin (7). The nozzle and guiderings are held in place by the nozzle ring set screw (4) and guide ring set screw (11)threaded into the body.

4-57



The guide (8A) is retained between the body (1) and bonnet (20) by the bonnet studs(21) and bonnet stud nuts (22).

The bonnet (20) contains the spring (13), spring washers (14 and 15), bearing adapterand bearing (18 and 17) and the spindle assembly (12), the lower end of which is posi-tioned on the disc bushing (5B) in the disc holder.

The adjusting bolt (33) is locked in place by the adjusting bolt lock nut (19) on top of thebonnet within the cap (23).

Manual lifting means is provided by the lever (25), lever pin (26), forked lever (28),forked lever pin (29), and spindle nut (31).

The operation of the valve is identical to that covered in Section 4.1.2.2.1 for two-ring-control safety valves and will not be repeated.

4-58



31

23

33

26

27

15

25

14

21

22

8A11

4

3

6

2

1

7

10

5B

5A

12

20

13

17

18

19

29

28

(a)Crosby Single Outlet

6R10 HA-FN Safety Valve

(b)Crosby Dual Outlet6R8X8 Safety Valve

Figure 4-32 (a-b)Typical Crosby Model HAFN MSSVs

4-59



BA 10 1A1B11A59111312143A1D1C6B6C

8186A

721918

A17

16A

16 17A

19 7A 15A

3

BB

13A

CO

NS

OLI

DA

TE

D

4 2 3A

3

4

SIN

GLE

OU

TLE

T

DU

AL

OU

TLE

T

OU

TLE

TF

LAN

GE

RE

MO

VE

D

Figu

re 4

-33

Typi

cal D

ress

er T

ype 1

700 M

SSV

4-60



The Crosby main steam safety valve is manufactured in a variety of inlet (welded,flanged and studded) and body configurations (cast body and forged). The valve seatdesign, as in the pressurizer safety valve, is also supplied in a variety of seat designsand material configurations that are dependent upon the inlet fluid conditions.

Dresser MSSVs

The Dresser Type 1700 safety valve is shown in Figure 4-33. This figure shows the dualoutlet safety valve in cross section and covers the essential elements of the valve with afull nozzle construction. It also shows the body (base) shape for a single outlet valvewith a semi-nozzle construction.

The basic elements of the safety valve consist of the valve body (base) (1A) which con-tains the nozzle (1B). Within the body (1A) is the disc (5), disc holder (12) guide (14) andspindle (8). Above the body is the yoke rod support (3A), the spring (6C), and the topand bottom spring washers (6A and 6B). Spring load is transmitted to the disc (5)through the spindle and retained by the compression screw (7). The yoke (2) and yokerods (3) are fixed in place at the body (1A) and yoke (2) by the yoke rod nuts (4). Theperformance characteristics of the valve are similar to that of the full-lift, reaction-type,two-ring-control safety valve discussed previously.

Design Comparison/Crosby and Dresser MSSVs

The following is a brief comparison of a few of the important features of the Crosby andDresser safety valve. The comparison should aid in the understanding of various as-pects of each valve design.

Both valve designs have an inlet nozzle type construction with a flat seat. In the Dresserdesign, the spring load is directly transmitted to the disc insert through the spindle point.In the Crosby design, the spring load is transmitted through the spindle point that has ahardened ball, then to a hardened bushing, and finally to the disc insert. In the Dresservalve, the spring load is retained through the use of (side) yoke rods that are fixed at thelower end by the valve body and at the top of the valve by a yoke. Crosby retains thespring load in a more conventional exposed spring safety valve bonnet design that isbolted to the valve body. This bonnet is called an open bonnet construction (as comparedto the closed bonnet used in safety relief and relief valve designs).

Both valve designs have the full-lift, full-nozzle, two-ring control that uses a huddlechamber and reaction principle to achieve the desired valve operation.

4.2.5 Auxiliary and Secondary System/BOP Safety Relief and Relief Valves

General Description

Safety relief and relief valves used on auxiliary and secondary systems are as varied indesign and applications as are valve manufacturers. Such valves are manufactured in abroad scope of design sizes, inlet and outlet connections, construction materials, andservice conditions (namely fluid, inlet design pressures, set pressure, outlet design

4-61



pressure, and backpressure). Typically these valves are manufactured by Crosby,Dresser, Farris, Lonergan (now Kunkle Valve), Target Rock and Anderson Greenwood.

Manufacturers produce these valves with inlet connections that range in size from 1/2-to 10-inch nominal pipe size. The flange inlet connections are ANSI Class 150 to Class2500 and, depending upon valve size and set pressure. Welded inlets can be socket orbutt welded. Screwed connections are also available. However, flanged connections arepopular because they permit the valve to be easily removed from the system for mainte-nance or repair.

Depending upon the system requirements and location on the nuclear plant, thesevalves can be manufactured to one of the following standards: ASME Section III, Sub-section NB, NC or ND and Article NX7000 or to ASME Section VIII.

Materials of construction of the valve enclosure (body and bonnet) and the valveinternals (nozzle, disc, disc holder, spindle, adjusting rings) may be, for example, car-bon steel, stainless steel, Monel and bronze. Material selections will vary as a function ofthe PRV service conditions.

Most PRVs use metal seats that are beveled or at a flat seat angle. Soft seat safety reliefand relief valve applications can be installed on systems where improved seat tightnessover that obtained from standard metal-to-metal seats is desired. Examples of serviceapplications where a soft-seat design valve could be used to improve seat tightness are:

• Where the system operating conditions for a safety relief valve (gas service) are lessthan 10% below the valve set pressure. (This is a standard design condition.)

• On systems where light gases are used.

• On gas systems that could expose the valve seat to foreign material such as pipescale, sand, or dust particles that may damage a metal-to-metal seating surfaceduring relief.

• The O-ring seat seal will preclude the damage that could occur from foreign par-ticles. When the valve closes on this type of foreign material, or if it is embedded inthe resilient O-ring, the valve tightness may not be impaired. If it is, it will only benecessary to change the O-ring to stop the leakage.

All of the valve manufacturers mentioned above use what is generically called a “softseat design”. This seat design may use an elastomeric (resembling or containing rubber)seat material or a polymeric material such as Teflon.

The major difference is the design of the valve disk which now has the O-ring to assistin effecting the seat seal. The valve still has all of the same internals as the conventionalvalve or balanced valve. A typical Dresser 1900 Series A, 45˚ metal-to-metal and O-ringseat is shown in Figure 4-34.

4-62



DISC RETAINING RING DISC

RETAINERSCREW

O-RING RETAINERO-RING SEAT SEAL

Figure 4-34A Soft Seat in a Dresser PRV

All of the above valves are manufactured as a conventional or balanced type design andhave a beveled, flat, or O-ring seat. The control/huddle chambers employ a fix or ad-justable (two-ring or single-ring)/low-lift or reaction-type design.

Since the designs of these PRVs are so varied, all the manufacturers and their valve typescannot be covered. However Figures 4-35 through Figure 4-41 identify somemanufacturer’s designs.

4-63



Noz

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Noz

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Rin

g

Dis

c w

ith B

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ng

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Spr

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Was

her

Cap

Gas

ket

Cap

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ustin

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olt

Adj

ustin

g B

olt

Lock

Nut

Gas

kets

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ndle

Spi

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Lock

clip

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et S

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olt L

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ut

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ket

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her

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Bon

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net S

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Bon

net S

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aske

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ilpie

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aske

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isc

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isc

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et S

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Cro

sby

Styl

e JO

and

JB S

afet

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elie

f and

Saf

ety

Val

ve

4-64



Figure 4-36Crosby Style JOS and JBS Safety Relief and Relief Valve

(Conventional and Balanced)

4-65



PC. NO. DESCRIPTION 1 BODY 2 BODY STUD 3 NOZZLE 4 DISC 5 GUIDE & RING 6 SET SCREW 7 SET SCREW GASKET 8A* SPINDLE 8B* SPINDLE BALL 9 SPRING 10 SPRING WASHER 11 12 BONNET 13 BONNET STUD 14 BONNET STUD NUT 15 BONNET GASKET 16 ADJUSTING BOLT 17 ADJUSTING BOLT NUT 18 CAP 19 CAP GASKET 20 CAP PLUG 21 CAP PLUG GASKET 22 CAP PLUG CHAIN 23 CAP PLUG CLIP 24 TEST ROD 25 IDENTIFICATION PLATE 26 NAME PLATE 27 DRIVE SCREW 28 SEAL & WIRE 29 SEAL CLIP

* Furnished as sub-assembly only

VIEW SHOWINGVALVE GAGGED

OUTLET

INLET

FingerTight Only24

2318

20

16

17

29

28

8A

12

13

14

15

4

6

7

8B

15

3

2

10

9

10

19

21

22

Figure 4-37Crosby Style JMAK Liquid Relief Valve

(Water Ring Design)

4-66



252427

232926353414

17

15334

101113B

92

1

213031

13A

19202215

32 33

28

VIEW SHOWINGVALVE GAGGED

45°± 5°

3A

3C

3B

3D

1

LIST OF PARTSPC.NO DESCRIPTION

1 BASE2 BASE GASKET3 DISC3A* DISC3B* DISC COLLAR3C* DISC COLLAR PIN3D* "O" RING

9 GUIDE & RING10 SET SCREW11 SET SCREW GASKET

13A* SPINDLE13B* SPINDLE BALL14 SPRING15 SPRING WASHER

17 CYLINDER

19 ADJUSTING BOLT20 ADJUSTING BOLT NUT21 CAP22 CAP GASKET23 DOG CAM24 DOG CAM BEARING25 DOG CAM BEARINGGKST26 O-RING27 LEVER28 LEVER PIN29 LEVER SPACER30 SPINDLE NUT31 SPINDLE NUT COTTER32 CAP PLUG33 CAP PLUG GASKET34 SEAL & WIRE35 SEAL CLIP36 TEST ROD37 DATA PLATE38 NAMEPLATE39 IDENTIFICATION PLATE40 DRIVE SCREW

Figure 4-38Crosby Style JMB-WR Liquid Relief Valve

4-67



SERIES 800ADJUSTABLE BLOWDOWNPRESSURE RELIEF VALVE

(a)

SERIES 900 OMNI-TRIMFIXED BLOWDOWN

PRESSURE RELIEF VALVE(b)

Figure 4-39 (a-b)Crosby Series 800 and 900, Omni Trim with Screwed Inlet and Outlet

(Valve Is Also Supplied with Flanged Connections)

4-68



O-R

ING

SO

FT

SE

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re 4

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)

4-69



Pac

ked

Cap

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ease

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Leve

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ew

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Spr

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her A

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elie

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Rel

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Figu

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4-70



CAP, PLAIN SCREWED

STEM

SPRING ADJUSTING SCREW

JAM NUT (SPR. ADJ. SCR.)

CAP GASKET

UPPER SPRING BUTTON

BONNET

SPRING

LOWER SPRING BUTTON

STEM RETAINER

PIPE PLUG (BONNET)

SLEEVE GUIDE

BODY STUD

HEX NUT (BODY)

BONNET GASKET

BODY GASKET

LOCK SCREW (D.H.)

DISC

DISC HOLDER

WIRE SEAL

LOCK SCREW GASKET

LOCK SCREW (B.D.R.)

HEX. NUT (B.D.R.L.S.)

LOCK SCREW STUD

BLOW DOWN RING

PIPE PLUG (BODY) 1/2 M.N.P.T.

BODY

NOZZLE

FARRIS SAFETY RELIEF/VALVECONVENTIONAL DESIGN

TYPICAL INTERNALS OF CONVENTIONALSAFETY RELIEF/RELIEF VALVE DESIGN

TYPICAL INTERNALS OF BALANCEDSAFETY RELIEF/RELIEF VALVE DESIGN

Figure 4-41Typical Farris 2600 Series Safety Relief/Relief Valve

5-1



5FAILURE MODES AND FAILURE CAUSE ANALYSIS

5.0 Introduction

This section discusses the failure mode and cause analysis (FMCA) performed in supportof the other sections of this manual. The FMCA is based on PRV failure information gath-ered from USNRC LERs and the INPO NPRDS data bases. Additional industry informa-tion was used when available.

This section presents the failure mechanisms and cause categories for valves installed inboth BWRs and PWRs. The intent of the analysis is to identify failure causes where main-tenance resources can be applied to enhance the performance of safety and relief valves.

Safety and relief valve maintenance information was collected for three principal ven-dors: Crosby, Dresser, and Target Rock. These vendors represent the predominantvalves used in ASME, Section III applications. The valves are typically used in reactorcoolant system (RCS), main steam system (MSS), and as automatic depressurizationsystem (ADS) valves.

5.1 Failure Mode and Cause Analysis

This section presents failure modes and causes for safety and relief valves used at bothPWR and BWR reactor facilities. Industry failure information was individually reviewedto categorize each reported failure mode and cause. This provided a common analyticalbase for each reported failure. A failure mode refers to the way a PRV fails, e.g., lift high,lift low. A failure cause refers to the physical cause of the failure. Failure causes can berelated to human errors, mechanical defects, service stresses, and wearout.

The identified fundamental failure modes for PRVs are listed below. Failure causes foreach failure mode are listed in Table 5-1. The failure modes and their associated causesare discussed in more detail in Section 5.2, Failure Mode and Cause Classification.

• Failure to lift (stuck shut)

• Lift high

• Lift low

• Seat leakage

• Failure to reseat

• Blowdown

• External leakage

5-2



Table 5-1PRD Failure Modes and Causes

sesuaCeruliaF sedoMeruliaF

eruliaFtfiLot

tfiLhgiH

tfiLwoL

taeSegakaeL

eruliaFtaeseRot nwodwolB lanretxE

egakaeL

eruliaFniPreniateRgniRgnitsujdA X

sgnitteSgniRgnitsujdA X

gnigA X X X

ylbmessA X

eruliaFeciveDtfiLyrailixuA X X X X

eruliaFswolleB X X

metStneB X X X

gnidniB X

egakaeLydoB X

gnidnoB X

sgnirpSnekorB X

noisorroC X X X

eriwkcoLnekorB/niPrettoC X

ngiseD X

egakaeLtaesevissecxE X

lairetaMngieroF X X X X X

tuhSdeggaG X

tnemtsujdAgniRnwodwolBreporpmI X

egakaeLegnalFtelnI X

laeSpooL X X

gnitseT/ecnanetniaM X

)taeS(tcefeDgnirutcafunaM X

ycneicifeDlairetaM X

gnidaoLelzzoN X X

egakaeLegnalFteltuO X

eruliaFtoliP X X X X

egakaeLtoliP X X

gnidaoLepiP X

larudecorP X X X

telnIdeggulP X

gnildnaH&gnippihS X

noitaxaleRgnirpS X

snoitidnoCtseT X X

ssertSlamrehT X

5-3



5.2 Failure Mode and Cause Classification

PRV failures were reviewed to uniquely classify each failure mode and cause category.This classification was necessary to provide a common reference from which the body ofvalve failure information could be analyzed. All incomplete failure data was substanti-ated by the use of other supporting information. In most cases, USNRC LER informationwas used to verify the extent of the failure(s) and number of valves identified in thereport.

Failure mode grouping uses similar failure causes, e.g., aging, test conditions, proce-dures, etc. This failure mode grouping provides a common link between the USNRCLER and INPO NPRDS information. Table 5-1 presents each failure mode with thepredominate failure causes.

5.2.1 Failure Modes

The following are descriptions of the important failure modes:

Failure to Lift (Stuck Shut): This failure mode deals with valves that did not open whenrequired. Causes that lead to this type of failure are the installation of the valve stemgag, valve disc physically restrained by corrosion products, or a plugged inlet.

Lift High: This failure mode deals with the valve lifting at a pressure greater than theallowable pressure as established by licensee’s Technical Specifications or by procedureacceptance criteria. Failures in this category are reported regardless of valve name platetolerance.

Lift Low: This failure mode deals with the valve lifting at a pressure less than the allow-able pressure as established by the licensee’s Technical Specifications or by proceduralacceptance criteria. Failures in this category are reported regardless of valve name platetolerance.

Seat Leakage: This failure mode refers to the condition where the valve exhibits processfluid leakage specifically past the valve disc and seat with normal system pressureapplied. Leakage outside the valve body is categorized as external leakage.

Failure to Reseat: This failure mode refers to the condition where the valve does notreseat after lifting. This is attributed to the shifting of the valve internal componentsduring the lifting process resulting in binding of the sealing surfaces.

Blowdown: This failure mode refers to the condition where the valve reseats after liftingbut reseats lower than the desired reseating pressure. This is attributed to nozzle ringadjustments or mechanical weakening or shifting of the valve components such that thevalve fails to reseat within the desired band.

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External Leakage: This failure mode refers to leakage other than seat leakage. Externalleakage includes body-to-bonnet leakage, inlet and outlet flange leakage, and bellowsleakage.

5.2.2 Failure Mode CausesThe following list identifies each failure mode cause and its effect on the valve.

Adjusting Ring Retaining Pin Failure: allows the adjusting ring(s) to move from their setposition which affects accumulation and blowdown

Adjustment Ring Settings: improper ring settings provided by the vendor for the appli-cation or applied during maintenance

Aging: assigned to valves which remained in service for extended periods of time withlittle or no PM performed

Assembly: installation of wrong valve part(s) and/or incorrect assembly procedure

Auxiliary-Lift Device Failure or Associated Inputs: 1) includes pressure inputs for ADSvalves such as pressure switches; 2) inputs that are stuck and/or prevent the valve fromclosing after lifting

Bellows Failure: 1) mechanical damage or failure of the bellows that causes system fluidto leak from down stream sources; 2) internal bellows failure that interferers with theability of the valve to reseat

Bent Stem: 1) valve stem mechanical damage; 2) valve stem is bent causing inadequatedisc and seat contact; 3) sufficient bending to prevent reclosure after opening

Binding: 1) physical rubbing of the valve stem and other components; 2) internal orexternal binding of the stem, disc, or other internals

Body Leakage: porosity of the valve body

Bonding: physical surface bonding of the disc and seat seating surfaces (typical wheredisc and seat materials are similar)

Broken Spring: main spring weakening or failure

Corrosion: 1) corrosion of the upper spring housing and chamber; 2) corrosion prevent-ing the valve stem/disc from lifting within the required pressure range; 3) valve discand/or seat surface corrosion resulting in seat leakage; 4) valve corrosion that interfer-ers with the ability of the disc and seating surfaces to provide a leak-tight seal

Cotter Pin / Broken Lockwire: a condition where a valve locking nut can reposition duringvalve lift and interfere with valve closure after opening

Design: applications where system operating pressure range and valve lift setpoint arevery close causing improper valve operation

5-5



Excessive Seat Leakage: conditions where the lift setpoint could not be determined due toexcessive valve main seat leakage

Foreign Material: 1) material left or remaining in the valve chamber preventing stemand/or disc lift; 2) material left or remaining in the valve chamber preventing stem liftwithin the desired pressure range; 3) material left or remaining in the valve chamberallowing process fluid to escape between the seat and disc; 4) material that becomeslodged in the valve during lift and prevents valve seating

Gagged Shut: valve stem gag not removed after installation

Improper Blowdown Ring Adjustment: mechanical adjustment that prevents the valvefrom reseating after opening

Inlet Flange Leakage: improper inlet flange torque, gasket installation, or alignment

Loop Seal: 1) applications were inlet loop seals affect valve performance; 2) the influenceof the loop seal causes valve body heating and/or thermal expansion of valve compo-nents

Maintenance/Testing: the ineffective maintenance techniques and testing program and/or testing controls

Manufacturing Defect: defects in seating materials that result in stress cracking or corro-sion failures

Material Deficiency: porosity in the disc, seat, or nozzle

Nozzle Loading: inlet and outlet valve flange loading due to thermal growth of valvestructural support components

Outlet Flange Leakage: improper outlet flange torque, gasket installation, or alignment

Pilot Failure: 1) applicable for all pilot actuated valves that are not lift device or pressuresensor input failures; 2) applicable to valves with pilot operation where the pilot causesthe valve to open above the desired pressure range; 3) leakage of the pilot causing valveactuation below allowable tolerance band; 4) input from the pilot that prevents thevalve reseating

Pilot Leakage: 1) pilot seat leakage; 2) external leakage from the pilot interconnections

Pipe Loading: similar to nozzle loading where support members thermally grow causingvalve body distortion that results in seat leakage

Procedural: 1) inadequate incorporation of vendor instructions in approved stationmaintenance procedures, programs, or test procedures; 2) maintenance procedures thatresult in poor sealing surfaces

Plugged Inlet: covers physical solidification of the inlet fluid

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Shipping and Handling: sealing damage as a result of shipping or handling

Spring Relaxation: main valve spring weakening causing reduced seating forces

Test Conditions: cases where plant test conditions were not stable

Thermal Stress: as a result of unplanned valve body heat up or operating environment.

5.3 Safety and Relief Valve Failure Data

Many sources of information were available for review. However, the primary sourcesof raw data used were obtained from the INPO NPRDS and the USNRC LER databases. The PRV failure data was combined into one data base. Other referenced sourcesof information provided a summary of the raw information in the form of regulatoryconcerns, recent industry topics, and helpful operational and maintenance reminders.These industry reviews were used to determine if data trends were consistent. Addi-tionally, vendor site visits and select utility interviews were performed to discuss opin-ions on the principal failure modes, mechanisms, causes, and the efforts to improvesafety and relief valve performance.

The information review was performed for all reported failures involving primary sys-tem safety valves, pilot operated relief valves, main steam system safety valves (includ-ing ADS valves), and relief valves. It is recognized that there are other failures that mayhave occurred that were not reported. However, these non-reported failures are notconsidered significant for the purposes and conclusions presented by this guide. Failureinformation was included from the earliest available data beginning in 1974 and endingon March␣ 1993.

Table 5-3, NPRDS and LER Safety and Relief Valves Failures (1974-1993), illustrates datafor each of the seven failure modes. This information is presented by plant type forBWR and PWR applications. In total there are 3,418 reported failures, consisting of:

• 272 primary safety valves

• 1,374 main steam safety and ADS valves

• 1,749 relief valve failures

The safety and relief valve population includes PWR primary valves and MSSVs andBWR MSSVs and ADS valves. The relief valve population includes systems rangingfrom diesel generator starting air and jacket cooling water, heat exchanger, and compo-nent cooling water relief valves.

5-7



Table 5-2NPRDS and LER Safety and Relief Valve Failures (1974–1993)

yrogetaCeruliaF epyTevlaVybseruliaFdetropeRrorebmuN

epyTtnalP RWP RWB +RWPRWB

epyTevlaV VSP VSSM VROP VSSMVSDA+

feileRPOBsevlaV slatoT

tfiLoteruliaF 0 2 5 36 82 89

hgiH—tfiL 55 402 0 153 132 148

woL—tfiL 28 902 2 26 683 147

egakaeLtaeS 611 312 11 361 657 9521

taeseRoteruliaF 1 62 5 81 451 402

nwodwolBreporpmI 3 3 0 32 5 43

egakaeLlanretxE 51 8 0 92 981 142

slatoT 272 566 32 907 9471 8143

PSV: Pressurizer safety valve ADS: Automatic depressurization safety valve

PORV: Power-operated relief valve PWR: Pressurized water reactor

BWR: Boiling water reactor BOP: Balance-of-plant

MSSV: Main steam safety valve

5.3.1 BWR MSS/Relief Valve Failures

Figure 5-1(a) illustrates the most frequent BWR MSSV/relief valve failure modes. Themost frequent failure causes associated with lifting higher than setpoint, seat leakage,failure to lift, and lift low are shown in Figure 5-1(b) through 5-1(e). The remainingfailure modes, failure to reseat, improper blowdown, and external leakage, are almostequally represented among the failure causes listed in Table 5-1.

5-8



(a)

(b)

(c)

Figure 5-1 (a-c)BWR Safety Relief Valve, Failure Modes and Causes

5-9



(d)

(e)

Figure 5-1 (cont.) (d-e)BWR Safety Relief Valve, Failure Modes and Causes

5-10



5.3.2 PWR Pressurizer Safety Valve Failures

The most frequent failure modes for PWR pressurizer safety valves are shown in Figure5-2(a). The highest seat leakage causes are shown in Figure 5-2(b). The second highestfailure mode, lift low, was caused most frequently by aging as shown in Figure 5-2(c).The third highest failure mode was lift high (see Figure 5-2(d)) with aging again beingthe most frequently reported failure. The data indicates that for all pressurizer safetyvalve failures the single largest failure cause was aging. If time-directed PM was sched-uled more frequently, the potential to affect 93% of all of the reported failures appearsfeasible. Although a total reduction of failures is improbable, a significant reduction inthe total number of failures could be obtained. The other significant failure mode,external valve leakage, was primarily caused by inlet flange leakage attributed to im-proper gasket installation or improper inlet flange torque. Other failures such as failureto reseat and improper blowdown were not found to be dominant failure modes.

(a)

(b)

Figure 5-2 (a-b)PWR Pressurizer Safety Valve Failure Modes and Causes

5-11



(c)

(d)

Figure 5-2 (cont.) (c-d)PWR Pressurizer Safety Valve Failure Modes and Causes

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5.3.3 PWR MSSV Failures

Figure 5-3(a) shows the most frequent MSSV failure modes in PWRs. Major failurecauses are shown in Figures 5-3(b) through 5-3(d). The remaining failure modes, failureto lift, failure to reseat, improper blowdown, and external leakage, are minor in thenumber of reported failures. Failure related to aging is the dominant cause of MSSVperformance problems. A detailed review of aging and bonding related failures wasperformed to determine if these cause categories were being used as the most reason-able causes when there where no other identifiable causes. The review determined thatthere were reports that identified failure cause codes as “aging” when there was noother identifiable cause. Consequently, this review classified age related failures of lessthan 24 months as being indeterminate. These were assumed to have been categorizedwith aging when there was no obvious failure cause. However, this category of indeter-minate failures represented only 19 out of a total of 665 reported MSSV failures.

(a)

(b)

Figure 5-3 (a-b)PWR MSSV, Failure Modes and Causes

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(c)

(d)

Figure 5-3 (cont.) (c-d)PWR MSSV, Failure Modes and Causes

5-14



5.3.4 PWR PORV Failures

The PWR PORV failure modes are included in this report to recognize that there arePORV failures. However, the total number of reported failures was small for the num-ber of PORVs in service and the number of years included in this review, with only 23reported failures over the past 19 years. Figure 5-4 illustrates the distribution of thereported failure modes. The failure causes are fairly low in number with a similar distri-bution to that of the PWR pressurizer safety/relief valves. The most frequent failuremode is seat leakage which had a primary failure cause identified as aging. Most agingfailure causes were closely grouped with age at failure being reported in excess of 120months. All age related failure cause codes were greater than 48 months. The secondmost frequent failure mode was split between failure to lift and failure to reseat. Thefailure causes associated with these failure modes were mixed between foreign material,ALD failure, broken stem, binding, and pilot failure.

Figure 5-4PWR PORV Failure Modes

5.3.5 Relief Valve Failures

Relief valve failures represent the largest number of reported failures. Figure 5-5(a) is achart of the most frequent relief valve failure modes. These reported failures representrelief valves typically found at both BWRs and PWRs. As previously mentioned theserelief valves include thermal reliefs, pump suction and discharge, and air system reliefvalves. The most frequent failure mode was seat leakage with the primary failure causebeing aging as shown in Figure 5-5(b). The average age at failure was 112 months. Therewere 81 reports where the failure cause was indeterminate. The next most frequentfailure mode, lift low, also had aging as the primary failure cause as shown in Figure 5-5(c). The average age at failure was 104 months. There were 44 reports where the failurecause was indeterminate. The next most frequent failure mode was lift high and againthe primary failure cause was aging shown in Figure 5-5(d). The average age for lift

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high failure mode was 115 months. There were seven indeterminate reports with themajority of these reports identifying bonding as the failure mechanism.

(a)

(b)

Figure 5-5 (a-b)Relief Valve, Failure Modes and Causes

5-16



(c)

(d)

Figure 5-5 (cont.) (c-d)Relief Valve, Failure Modes and Causes

5.4 Failure Modes Analysis

The predominant failure mode for all valve types is lifting outside the desired pressurerange. There were approximately 1,580 cases reported for all valve types (pressurizer,main steam, and relief valves). The major contributor for this failure mode includes MSSVwith 826 reported failures outside the required pressure range (high and low). Reliefvalves (all types) are the next largest contributor with 617 reported failures outside therequired pressure range. The pressurizer safety valve is next with 137 reported failures.

The predominant failure mode for all safety valves is the MSSV lifting higher than thesetpoint value. A review of the specific data indicates that most of these failures areoutside the ± 1% allowable but within the ± 3% vendor design tolerance. These lift

5-17



setpoint failures are principally driven by the close tolerance between TechnicalSpecification requirements and the actual ability of the valve to perform within therequired pressure band. This was identified in the Special Report AEOD/S92-20. Thisreport identified that approximately 70% of all the reported safety valve malfunctionsare attributed to the condition called “setpoint drift.”

The term “setpoint drift” should be changed to “setpoint variance” in most cases. Thereason for distinction between the two terms is associated with the results of continuedvalve testing after the first lift of the valve. Often the first lift of the valve is outside the±1% range but is normally within the ±3% range. Then, in many cases, the second, thirdand fourth lift tests result in the valve lifting within the ±1% range without valve adjust-ment. This lifting phenomenon appears to be normal for the type of valves being usedby the industry. Tests are being conducted by the BWR Owners Group and others tounderstand this phenomenon.

A survey was conducted to gain a better understanding of the industry’s response tothe setpoint variance problem. This survey found that 50% of those responding hadrequested relief from technical specifications that require corrective action and a 30 dayreport when a code safety valve has an as-found set pressure outside a ±1% tolerance.However, if this relief is granted, it is recommended that safety valves going into ser-vice should be set to within the ±1% tolerance and the ASME/ANSI OM-1987 Part 1allowance of a tolerance of ±3% for valves should be used as the acceptance criteria forinservice valves. It should be kept in mind that an engineering review of the relievingcapacity versus the associated valve lifting setpoints be considered as part of any re-quest for changing the setpoint limits.

The next major failure mode for all valve types is seat leakage with 1259 identifiedcases. Relief valves are the major single contributor for this failure mode followed bymain steam and pressurizer safety valves.

Failure data analysis indicates that during the mid-80s safety valve performance wasmore closely followed then in previous years. Failure reporting increased substantially asa result of uniform reporting criteria provided by 10CFR 50.73 and after the results ofEPRI’s PWR Safety and Relief Valve Test Program and EPRI’s Safety and Relief Valve TestReport (EPRI NP-2628-SR) were published. Also, many facilities only tested their PRVsand performed corrective maintenance when required. This practice allowed PRVs toremain in service until age related failures started to occur. These aging failures could bereduced by performing routine scheduled maintenance on the valves. This maintenancecan be accomplished by valve rotation, and/or by periodic PM inspection and testing.

5.5 Causes of Failure Analysis

The following discussion addresses the most reported failure causes. Each failure causewas reviewed to ensure that the reporting was based on an actual determination ratherthan reaching this conclusion because no other failure cause could be determined.

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5.5.1 Aging

The population of PRDs assigned the aging cause category was based on the causenarrative and the component age at failure. Failures reported as aging that were lessthan 24 months were reclassified as indeterminate. Those failures that are identifiedwith ages greater than 25 months were left as originally categorized. There were 14 outof 116 reported PRV seat leakage failures that were reclassified as indeterminate. Therewere 77 out of 376 reported MSSV seat leakage failures that were reclassified as indeter-minate using this criteria. Based on the above numbers only, about 10% of the reportedfailures appeared to be reported incorrectly.

Valve testing and actual valve lifting due to service conditions is a form of aging in thatthe valve seat can experience wear and/or minor damage. The resulting damage cancause minor seat leakage which over time leads to valve failure both from an open pipeboundary concern and from the leakage effect on the valves setpoint. Testing of a leak-ing valve will not provide reliable results and thus should be avoided. Other compo-nents of a valve such as the bellows, stem, guides, or spring can also be damaged de-pending on the type of overpressure event that has occurred. This internal damage maynot be readily apparent using external inspection techniques. Valve internal inspectionsare required during the next scheduled outage for valves that have experienced anoverpressure event during the operating cycle.

The aging process is not just a time dependent mechanism but the result of the sum totalof events the valve has experienced within its operating environment. For example, if avalve is in a high temperature corrosive environment with all moving parts exposed, thevalve can experience corrosion resulting in wear or binding when actuated. The bindingcan cause fasteners to be fractured resulting in pin loosening or breakage. The data sug-gests that valve aging and resulting service wear are often hidden type failures that onlytesting or valve inspection can find. Many of the reported valve testing failures can beavoided by a more routine schedule of valve inspection/maintenance and not waiting fora valve testing failure to occur prior to repair. Keep in mind that since aging of a PRV isassociated with the sum total of events either from testing or from inservice actuation,valve failure can be avoided if refurbishment is performed prior to actual failure. Also,keep in mind that valve testing is designed as a failure finding task and valve test failuresshould not necessarily be looked upon as a bad outcome.

5.5.2 Disc-to-Seat Bonding

Corrosion bonding of the disc to the seat is caused by the formation of a black, hard,tightly adherent oxide film that covers the exposed disc and seat area. If there is nometallurgical indication that an oxide film is present bonding is probably not the reasonfor a valve’s failure. If bonding is determined as the reason for valve failure, a metallur-gical determination should be conducted that decides to either prevent the corrosionfrom occurring or the necessary maintenance actions needed to maintain the valve’soperating performance.

5-19



The bonding cause category was assigned when the reported failure cause is describedas bonding by the narrative and when associated with the lift high failure mode. Allreported failures were individually reviewed to determine if physical bonding wasidentified. Those reports that did not specifically discuss actual findings were catego-rized as indeterminate. There were only a few cases where the bonding cause wasreclassified as indeterminate. It should be understood that bonding studies are beingconducted by owners groups, vendors, and individual utilities, and no definite conclu-sion can be made at this time. Also, most reported bonding problems have been associ-ated with the pilot section of pilot operated valves.

5.6 Failure Significance on Outage Durations

An evaluation was conducted on information collected from 1988 to 1992 on plantoutage time caused by PRV maintenance. The data indicates that BWRs experienceapproximately 16 days per year of unplanned plant outage time as a result of safety andrelief valve maintenance activities. PWRs experienced the following unplanned plantoutage durations:

• MSSVs 7 days per year

• PSVs 42 days per year

• PORVs 11 days per year ( small sample size)

• Relief Valves 4 days per year (for both BWRs and PWRs)

Since unplanned outage durations represent lost generation time, a plant experiencingthese failures could improve its capacity factor by preforming planned maintenance onthose valves experiencing aging as the main cause of failure. PRD failures from 1988 to1992 caused each plant the following average lost generation revenue each year:

• BWRs $16,000,000

• PWRs $64,000,000

Each maintenance organization is encouraged to review their safety and relief valvemaintenance schedules and consider the following planned maintenance schedule:

• Rebuild MSSVs at least every 36-48 months

• Rebuilding PSVs every second fuel cycle

• PORV rebuilding every second to third fuel cycle

• RV rebuilding every 60 to 72 months

This increased valve maintenance can prevent most failure modes associated with agerelated valve failures and seat leakage. Section 8 of the guide address the type of main-tenance actions that should be considered to enhance your safety and relief valve main-tenance program.

6-1



6PRD TESTING

The purpose of this section is to examine practical testing methods that meet the differ-ent test requirements for PRVs in nuclear power plants. Appendix C summarizes therequirements of the test codes that govern inservice inspection (ISI) and testing ofsafety-related and non-safety-related relief valves in the nuclear industry. Prior towriting any valve test procedure, the current federal, state and insurance requirementsfor valve testing should be reviewed and understood. Plant ISI organizations shouldhave this information available or have the ability to obtain it from the plant’s assignedauthorized nuclear inspector.

Section 6 is a general overview of ASME Codes that address fired and unfired vessels.These overviews are not meant to cover all aspects of the Code but to provide importantaspects of each code. ASME Code requirements can change, so it is important to knowthe ASME Code year and addenda that govern the requirements of each plant. Thissection on testing uses the 1994 edition with the February 1995 addenda. The remainingsubsections discuss general testing guidance that has been used by various utilities toenhance safety valve testing programs.

6.1 Codes Governing Safety-Related PRV Testing

All nuclear power plants are required by Title 10 of the Code of Federal Regulations,Part 50.55a (10CFR 50.55a) to establish an ISI program in accordance with Section XI ofthe ASME Boiler and Pressure Vessel Code. Division 1 of Section XI deals strictly withlight-water-cooled plants, such as PWR plants and BWR plants built in the U.S. DivisionII and III deal with gas-cooled and liquid-metal-cooled plants, respectively, and are notcovered by this manual.

The purpose of an ISI program is to detect failures, defects, or discontinuities in thepressure retaining components essential for safety-related equipment and their sup-ports. An ISI program establishes the scope and frequency of inspections/testing thatwill ensure that plant equipment functions as designed. While the overall program isdefined in Section XI, it states that PRVs included in the ISI program should be tested inaccordance with one of two documents, depending on the edition of the ASME Boilerand Pressure Vessel Code that a plant has adopted: (1) the American National Standard,ASME/ANSI PTC-25.3 or (2) the Code for Operation and Maintenance of NuclearPower Plants, ASME OM Code. Although both documents stipulate mandatory testingrequirements for PRVs contained in the ISI program, they differ substantially in severalareas. See Appendix C for a detailed discussion of the ASME OM Code Appendix I 1994Edition and a comparison of these two documents.

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Note: ASME PTC-25.3 has been revised as ASME PTC-25 in 1994.

6.2 Codes Governing Non-Safety-Related PRV Testing

Because the Code covers the largest variety of vessels, most BOP safety valves aregoverned by Section VIII, Pressure Vessels. Section VIII is comprised of two volumes,Divisions 1 and 2. Division 2 has alternative rules for the construction of pressure ves-sels based on the design-by-analysis methods of Section M. However, the overpressureprotection requirements of both divisions are virtually identical.

Section X, Fiberglass Reinforced Plastic Vessels, adopts the same basic overpressurerules as Section VIII, but is somewhat more restrictive as to the types of non-reclosingPRDs permitted.

6.2.1 Allowable Overpressure

Most PRDs, particularly PRVs, require an increase in pressure above set pressure definedas overpressure to achieve capacity lift. It is at this overpressure that the PRV’s ratedcapacity is determined and specified. Because some are allowed to be set above the maxi-mum allowable working pressure (MAWP), vessels with multiple valves may require aneven greater increase over the MAWP for all the relieving valves to open fully. Accord-ingly, each book section provides its own rules as to the percentage of pressure allowed toincrease above MAWP or design pressure during an overpressure event.

The Section VIII limits on overpressure depend on the type of installation. In generalSection VIII mandates that pressure not be allowed to rise more than 10% or 3 psig(whichever is greater) above MAWP. When multiple devices are used or additionaldevices are provided to protect against exposure to fire, overpressures of 16% or 21%respectively, are allowed. For valves that protect liquefied compressed gas storagevessels against exposure to fire, 20% overpressure is allowed.

Section X has the same overpressure requirements as Section VIII except that specialrules for protection of liquefied compressed gas storage vessels exposed to fire are notconsidered.

Each code section specifies various operational and performance requirements for PRVs.Some apply during testing and service, while others apply only during product provi-sional and production certification testing. For example, Section VIII imposes a five per-cent blowdown requirement during provisional certification testing and then only if theblowdown is adjustable. During production certification testing, this blowdown limit isincreased to 7%. When the manufacturer produces the product for shipment to a cus-tomer no limit is invoked. It is therefore important that the user understand the specifiedCode requirements for PRVs prior to performing any testing. This will assure that whenprocedures for testing are written, requirements more stringent that those required by theCode to which the valves were manufactured are not invoked.

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6.3 General Test Requirements

The main focus of any PRD testing program is to ensure that the measurements ob-tained during testing will permit accurate setpoint verification. It is equally importantto eliminate any variables present during the testing process that could affect the setpressure measurements. Tight control of the testing parameters and equipment helpseliminate the introduction of errors and will ensure an accurate, repeatable test. Thefollowing sections provide a general discussion of the factors that should be consideredfor a proactive PRV test program.

6.3.1 Test Methods

The test method will depend on a valve’s type of service, location and type of attach-ment (welded or bolted) to the system being protected. The ASME Code allows twoother types of testing:

• Bench testing on- or off-site test facility testing for large PRDs

• In situ testing with an ALD

Since testing is a failure finding type task, it is conducted as part of the valve repairprocess. First, to determine if any changes had occurred when the valve was on thesystem, and second, after a repair to confirm set pressure prior to reinstallation. Table6-1 is a general outline of the refurbishment and testing process for both on-site and off-site testing.

The most accurate method for testing the set pressure of a valve is to test it in the exactcondition that it is required to function. However, this requires the system to be taken tothe conditions its designed to protect against. In this method, the system pressure isincreased until the installed valve opens (i.e. self actuates). The system pressure is thendecreased until the valve reseats. If the valve set pressure is not within the requiredpressure tolerance the valve set pressure is adjusted and the test repeated until the setpressure is within tolerance. This testing technique is the most accurate because all ofthe factors that effect the valve such as system pressure, temperature, fluid characteris-tics, location and environment are actual valve service conditions. This is easily done forvalves on steam or a compressible fluid systems where valve open and close is easilydetected. It is difficult on liquid systems where visual observations of the valve openingcannot usually be done.

Set pressure test should generally be performed as the operating system is coming off-line. This will allow the testing to have minimal effect on plant operations and identifythe need for valve maintenance during the plant outage. The main disadvantage in thistest method is that it is time consuming, expensive, resource intensive and results in thedischarge of system fluid either to the atmosphere or to a safe disposal area. Further,this test method is not a recommended practice for testing PRVs installed on hazardousfluid systems. (For these applications, bench testing is the preferred testing technique.)

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Table 6-1Typical Valve Testing/Refurbishment Sequence

ACTIVITY SEQUENCE

PRD Receipt at Off-site Test Facility (a) Removal from shipping container(b) Radiation survey and initial decontamination(c) Receipt inspection(d) PRD preparation for test

As-found Steam Test (a) Pre-test leakage(b) Set Pressure actuation(c) Post-test leakage

Refurbishment (if required) (a) PRD fully disassembled(b) Component decontamination(c) Rework & dimensional inspection(d) PRD reassembled

OR(a) PRD partially disassembled(b) Component decontamination(c) Seating surfaces polished (“Jack & Lap”)(d) PRD reassembled

Recertification Test (After Full Disassembly)

Note: On some valve types, Item B may(if required) be performed followingrefurbishment but prior to the recertification test.

(a) Pre-test leakage(b) Operational verification of auxiliary (manual)

actuating devices(c) Set pressure actuation(d) Post-test leakage

Recertification Test(After Partial Disassembly)

(a) Seat leakage

PRD Packaging (a) PRD preparation for shipment(b) Final inspection & radiation survey(c) Placement in shipping container

6.3.2 On-Site Bench Testing

On-site bench testing is normally accomplished by setting the valve on a test stand thatcontains a limited volume accumulator. It is very important that the test stand be de-signed for the type of test that is to be performed. For non-compressible fluid valves,where the lift of the valve may be directly proportional to the inlet pressure, the designof the test stand is strictly a measure of pump capacity. For compressible fluids, such asair, gas, or steam, energy is stored in the compression of the fluid which is releasedwhen the valve lifts (pops). This release of energy is what causes the popping action incompressible service PRVs.

The volume of the accumulator and the size and length of the piping leading to the teststand are extremely important. The testing must ensure that the captured measure-ments are the mechanical characteristics of the valve and not characteristics of the teststand. Very little published guidance exists as to the sizing of accumulator volumesnecessary for testing PRVs. However, Appendix C of the National Board of Boiler andPressure Vessel and Pressure Inspectors publication, NB-65, provides curves for sizingaccumulators with the size of the accumulators based on performing an operational test.The curves are greatly oversized for limited lift set pressure testing.

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Recent research indicates that the size of the accumulator may affect the set pressure ofa safety valve. For example, testing a valve using a DOT bottle, a pressure regulator anda 3/4-inch line connected to a test flange may not yield the same set pressure as a teststand containing a 30 gallon accumulator. Factors that can cause these variations are: 1)tester inexperience; 2) valve seat condition; 3) fluid; and 4) valve set pressure. Conse-quently, changing the test stand equipment between testing periods may affect therepeatability of previous tests.

The required accumulator size is directly related to the maximum relieving capacity ofthe valve, i.e. the orifice size of the valve nozzle. The capacity of PRVs is determined by:

• The bore diameter of the nozzle (or seat bushing)

• The set pressure of the valve

• The rated lift of the valve

• The overall valve design

• Whether the valve lift is restricted during test

Bore diameter of the nozzles have been standardized by assigning alpha characters tothe different sizes, ranging from a “D” orifice (0.110-inch2) to a “BB2” orifice (185-inch2).Obviously, the capacity required for blowdown testing of an “F” orifice valve is sub-stantially less than that of an “R” orifice valve. To compensate for this volume, somemanufacturers recommend the position of the ring(s) be changed for bench testing. Formore information about bench testing, see Appendix E.

6.3.3 Auxiliary Lift Devices (ALDs)

ALDs operate by measuring the amount of force required in addition to the force pro-vided by the system fluid pressure to cause the valve to lift. The force measurement isconverted to a pressure per unit area and is summed with the existing system pressure atthe valve inlet to calculate the simulated set pressure of the valve. In order to measure theset pressure of a valve, the ALD must be able to capture the point at which the valveattains lift. With compressible fluid service valves, the lift of the valve makes the setpressure determination relatively easy. However, with liquid service valves, the point oflift is not so easily detected. Since the lift of liquid service PRVs may be proportional tothe applied force, it is difficult to pin-point the moment where lift has occurred. For thisreason, the ASME Code discourages or forbids the use of ALD on liquid service valves.

ALDs must be calibrated in order to ensure accuracy. ALDs use a variety of measuringinstruments ranging from analog gages and force transducers to acoustic frequencytransducers and linear variable differential transducers or transformers. Some of thenewer systems include strip chart recorders and computer controlled data acquisitionsystems to capture and document the results. It is important that certifications for thedifferent calibrated instruments be obtained prior to any testing. There should also be ameans of verifying the calibration of the equipment before and after the testing. Mostverifications use the shunt calibration method where a known resistance is placedacross the bridge of the transducer and a known voltage signal is applied. The resulting

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signal returned from the transducer must read between certain prescribed limits if thetransducer is in calibration. Systems employing analog gages should be checked with adead weight tester or other calibration verifying device. Testing with an ALD is dis-cussed in Section 6.4.1 and in Appendix D.

6.3.4 Developing a Repeatable Test

Control of the testing process (in situ, bench, or with an ALD) is essential if repeatabletest results are to be obtained. The five areas listed below must be carefully evaluatedand controlled so that errors are not introduced between tests:

• Environmental conditions

• Test equipment

• Test procedures

• Valve history

• Valve condition

When testing a PRV, it is important that the measurements obtained from testing are anaccurate indicator of the valve performance (free from errors induced during the testingprocess). Knowing the capabilities of the test equipment and the personnel performingthe test is essential. Accumulator size, the proper test media, gage ranges etc. must beproperly selected for the type of test that is to be performed. Also the required experi-ence level of personnel performing each task is essential to perform an accurate test.

6.3.4.1 Environmental Conditions

One of the most overlooked areas in safety valve testing programs is the effect of envi-ronmental conditions on the testing process. Things that must be considered whendeveloping a test program are:

• The temperature of the test fluid

• The temperature and media of the plant system

• The ambient temperature of the valve’s environment while installed in the plant

• Testing methodology

Deviations between the inservice plant system’s fluid temperatures and test fluid tem-peratures can cause the as-measured tested set pressure to differ from its inservice setpressure. BOP valves that are removed from a system and installed on a test stand areusually tested with air, gas, or water at room temperature (the exceptions to this arelarge steam valves, such as MSR steam safety valves, which are normally sent to an off-site testing facility for steam testing). Fluid temperatures in plant systems are normallymuch higher than the temperature of the test fluids. The conduction of heat from thesystem fluid through the valve can cause changes in the rigidity of the valve’s spring byreducing the modulus of elasticity of the spring metal. The effect may be a lowering ofthe set pressure. Manufacturers have recognized this fact and have published tables of

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correction factors that should be used when setting safety relief and relief valves wheretemperature differences exist. The correction factor is added to the stamped setpoint ofthe valve in order to calculate a temperature-weighted set pressure. Generally, tempera-ture correction factors are not employed on safety relief and relief valves (which arepermitted by Code to have a broader set pressure tolerance) unless the system fluidtemperature exceeds 149˚F. However, always check the valve manufacturer’s technicalmanual or with the manufacturer for a determination of whether a temperature correc-tion factor is necessary. Further, most manufacturers will, on ASME Section VIII CodeStamped (UV) valves, attach or mark on the nameplate a cold differential test pressure(CDTP) (see glossary for definitions). Section 6.5 describes the methods used to test forambient inservice valve temperature.

It is also important that a valve be tested with the same fluid it is exposed to inservice.Testing a steam service valve with air without using a correlation factor will lead todiscrepancies in set pressures. ASME Section VIII, Division 1, Paragraph UG-136 de-fines production testing requirements for a manufacturer. When testing valves onsteam, it is also important that the valve be allowed to come to thermal stability beforetesting between each lift. After each lift, a suitable amount of wait time should be al-lowed before another test is performed so that the valve can return to thermal stability.The standard wait-time between tests is five minutes, but more time may be needed.Attaching surface mounted temperature sensors on the body can assist in this determi-nation by measuring the valve’s temperature (see Section 6.5).

Temperature gradients across a valve can cause uneven thermal growth of the valvebody, internals, and spring as well as thermal distortion of the seating surfaces. Thethermal growth of parts caused by the fluid and ambient temperature can cause fluctua-tions in the spring force, thus causing the set pressure to change. Distortion of the seat-ing surfaces can cause seat leakage and instability of the pressure boundary between thedisk and nozzle seating surfaces.

It is important to recognize that insulation can also cause differences in the actual setpressure. Valve manufacturers recommend that PRVs may or may not be insulated.This recommendation can change based on fluid, service and valve location. However,many utilities commonly insulate PRVs for personnel safety reasons. The purpose ofinsulation is to reduce heat transfer, i.e., to prevent personnel from being burned. Re-ducing valve heat transfer will increase the temperatures experienced by the valve.Whenever possible, the same type of insulation should be used for off-site testing.Recent testing experience of PSVs at an off-site steam test facility without the normallyinstalled insulation caused a set pressure difference of minus 5% from the actual setpressure of the valve under installed conditions. This premature lifting was resolved bysending the insulation with the valve to the test facility and installing it on the valvethroughout the testing process.

6.3.4.2 Test Equipment

All test equipment and instrumentation used in the performance of valve testing shouldbe calibrated in accordance with utility quality assurance (QA) policies. This includes

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both on-site and off-site testing. Standards used for performing all calibrations shouldbe traceable to the National Institute of Standards and Technology.

Test equipment may be calibrated on a periodic basis with the calibration intervaldisplayed on a decal or on a pre and post test basis. Calibration frequencies should bebased on the utility QA requirements. In addition to individual component calibration,an end-to-end system calibration should be performed as necessary.

Recommended maximum allowable tolerances on test measurements are:

Temperature +/- 4˚F

Heise gage +/- 0.1% full scale

Deadweight tester or digigage +/- 0.03%

Pressure transducer +/- 1.0 psig

6.3.4.3 Test Procedures

Procedural control is one of the keys to ensuring repeatable tests. The testing processshould be documented step by step to ensure that the test practices are consistent be-tween testing periods. When testing a PRV on a test stand, the following minimuminformation should be included :

• Personnel safety and ALARA concerns

• Instruction for proper installation of the valve to the test stand

• Visual inspection criteria

• Pre-set pressure tightness criteria

• Maximum test pressure

• Temperature correction factors and alternative fluid correlation factors, if applicable

• Setpoint acceptance range• Acceptable pressure gage range and accuracy criteria for desired pressure

measurement

• Instructions for controlling the test bench when performing tests

• Set pressure adjustment instruction

• Blowdown and control ring adjustment criteria, if applicable

• Post test seat tightness criteria

• Bellows integrity testing criteria

• Imposed back pressure

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The criteria listed above are for PRVs in general. There will be information specific tothe individual type of valve to be tested, such as pilot or solenoid operated relief valves,that should be included in the test procedure.

It is important that a consistent “ramp rate” be obtained. The “ramp rate” is the rate atwhich the test pressure/force is applied to the valve in order to cause the valve to lift.Testing a PRV using a high ramp rate could cause the valve to lift at a perceived lowerpressure due to pressure ramp rate. Care should be taken to include a procedural state-ment concerning the speed of the pressure ramp rate. When testing compressible fluidservice valves, the test pressure should be raised to approximately 90% of the setpointand then increased 2 psig/sec until the set pressure is achieved. Rarely are there meansto determine and moderate the actual ramp rate so precisely. Normally, statements suchas, “Raise the system pressure to 90% of setpoint. Increase test pressure slowly until setpressure is reached,” will suffice.

6.3.4.4 Valve History

Test records allow the formulation of valve histories on individual valves, valve styles,valve groups, and valves in particular plant systems that can be used for trending. Withthe advent of computers and database programs, it is now very easy to run queries oncertain valves, valve types, manufacturers, and systems of valves to determine adversetrends and recurring problems. It is also useful for determining valves that were testedwith individual test instruments so that the effect of an out-of-tolerance can be evalu-ated. Test records in addition to the valve’s name plate data and serial should includethe following:

• The type and number of valves to be examined for each operating time period

• Procedures used in valve repair, testing and maintenance

• Results of examination

• Repairs and corrective action

• Modifications per the manufacturer

• Valve test schedules

• Results of tests

Nameplate data should also be included in the test report. The serial number on thenameplate of the valve can be used to obtain original test data and design/purchasespecifications from the manufacturer. Records should be kept for the time period ex-pressed in the utility’s Technical Specifications or for a minimum of four test cycles.

6.3.4.5 Testing Practices

Differences between test methods can also cause variances in the measured set pressure.Recent comparison studies between ALD and bench testing have been performed at anoff-site testing facility. The results of the study have shown that a small difference may

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exist between the set pressure value determined by each method. This difference cannormally be attributed to the following factor:

An ALD set pressure measurement is derived from determining the additional forcerequired above the test pressure to cause the valve to lift. This value is determinedbased on a derived seat area, while bench testing yields a direct pressure measurement.

Utilities that use an ALD for set pressure verification often remove valves that giveinconsistent results and send them to off-site testing facilities for repair and final setpressure testing. While it appears that the difference is small enough not to create a testfailure, the difference between the test methods does exist. For utilities that performALD testing as a means to verify the “as found” set pressure, it is advisable to resetthese valves using the same ALD so that the same test method is used to determine the“as-found” testing during the next testing period. As stated previously, in any testprogram it is important that the same procedures be followed.

6.3.4.6 Fluid Temperature Compensation

If the temperature of the plant system fluid differs from the temperature of the testfluid, a temperature correction factor may be needed. Generally, temperature correctionfactors for safety relief and relief valves are not recommended by valve manufacturers ifthe plant system fluid exceeds 149˚F since these types of valves, by the ASME Codes,have a broader set pressure tolerance than safety valves. The manufacturer’s technicalmanual should always be consulted when determining temperature correction factors.Many manufacturers stamp the valve’s nameplate with “cold differential setpoint”. Thecold differential set pressure is the desired setting of the valve compensated for thetemperature differences between the system and the test fluid.

6.3.4.7 Compensation for Superimposed Backpressure

Conventional Valve: If an unbalanced, conventional PRV discharges to a system or vesselwhere outlet of the valve is exposed to a constant backpressure, then the set pressuremust compensate for the back pressure.

Balanced Valve: If the valve contains a balancing mechanism, such as a balancing bel-lows, back pressure compensation is not necessary. The set pressure of an unbalancedvalve under constant back pressure is calculated by the following method:

Set pressure = Stamped setpoint - Backpressure

Note that this value is combined with the temperature correction to establish the totalCDTP.

As with any type of set pressure setting, the plant conditions under which the valve isinstalled must be considered.

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6.3.4.8 Determining Setpoint for Liquid Service Valves

Determining setpoint may be different for each valve manufacturer. Contact the manu-facturer or use the National Board Red Book to determine the correct method to be used.The method used can make a difference in determining what the actual setpoint is.When testing liquid service valves, the definition of the point at which set pressureoccurs must be clear. Set pressure can be defined as the first drop of water, the firstcontinuous flow, a specified number of drops, or when the valve disc separates from thenozzle seat. If a data acquisition system is used to record the test of liquid relief valveand a linear variable differential transformer is used to determine the moment wherespindle travel first occurs, only in the later definition can this equipment be an aid andonly on a full flow system.

6.4 In Situ Testing

In situ testing is the most accurate method to evaluate the set pressure of an installedPRV. If proper test procedures are employed, testing PRVs in place is called in situsystem pressure testing. In this method the system pressure is increased until the PRVopens (i.e. self actuates). The system pressure is then decreased until the valve reseats. Ifthe valve set pressure is not within the pressure tolerance (such as ±3%) the valve’s setpressure is adjusted and the test repeated until the set pressure is within the prescribedtolerance. Should actual set pressures vary above and below the allowed tolerancevalue during testing, the root cause should be determined and corrective action taken.This set pressure testing technique is the most accurate because all of the system factorsof pressure, temperature, fluid characteristics, valve installation and environmentalconditions are actual service conditions.

6.4.1 ALDs

In service applications where the PRVs are welded to the system and there is no reason-able way to raise the system pressure to the set pressure of the valves, the only means toverify the set pressure is the use of an ALD. In other applications where raising thesystem pressure to self-actuate the PRVs would adversely affect other componentsinstalled in the system, the use of an ALD is also required.

Properly used ALDs can accurately determine the set pressure of PRVs in situ underappropriate test conditions that follow proven test procedures. Pressure setpoint testshave been conducted using the ALD and then “pressure popping” the valve to determinethe actual set pressure. The tests have typically shown that the pressure set by the ALDwill normally fall within a band of ±1% of the actual set pressure. However, there hasbeen a number of valve testing failures caused by the improper use of ALDs. See Appen-dix D for more information about ALDs.

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The concept behind ALDs is simple. The device applies an auxiliary lifting force in con-junction with the system pressure in order to cause a PRV to lift. ALDs are recognized bythe major regulatory codes with the exception of the limit for use on liquids, such as:

• Section VII of the ASME Boiler and Pressure Vessel Code

• National Board of Boiler and Pressure Vessel Inspectors Publication NB-65

• Appendix I of the ASME OM Code

• ASME/ANSI Publication PTC-25.3


There are generally three guidelines shared by all of the codes:

• ALDs are an acceptable means for setpoint verification

• ALDs should only be used on systems containing compressible fluids

• Blowdown cannot be measured using an ALD

6.4.1.1 ALD Design

The design of an ALD normally consists of three basic components:

• Power source

• Mechanical frame

• Setpoint indicator

The power sources that drive ALDs are diverse. They range from a hydraulic oil hand-pump supplying hydraulic cylinders to sophisticated pneumatic or electric drivenhydraulic pumps with microprocessor flow valves to regulate the ramp rate of theauxiliary force provided by hydraulic cylinders.

The load-bearing structure of the ALD is the mechanical frame. It provides the connec-tion to the valve spindle (where the auxiliary spindle lifting load is applied) and mountsthe system securely to the valve yoke or bonnet. Load bearing structures are designedto provide the high lifting forces necessary to test large valves or valves with highnameplate set pressures.

The setpoint indicator is the most critical part of an ALD. The setpoint indicator canrange from something as simple as a mechanical bourdon tube type gage to a digitalmicrocomputer-based data acquisition system that simultaneously records the appliedauxiliary load, valve spindle travel, system pressure, acoustic monitoring of the valve,and various outputs from the thermocouple. Microcomputer-based systems generallyhave video screens that simultaneously display the sensors’ outputs in near-real time(digital or graphical form - signal versus time). Usually, this information is stored forplayback, hard copy dump, or downloaded to a personal computer through a disc or acommunications port for further analysis. Some units also have the capability to expandareas of the graphs produced to allow further analysis.

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6.4.1.2 Setpoint Determination

The differences between the individual ALD systems are generally found in the meth-ods used to capture the point in time where the valve opening occurs and the conver-sion of the data acquired into an actual set pressure. There are basically two differentschools of thought. The first school of thought derives the setpoint based on empiricalcurves. This is done by developing a fitted curve for each orifice of a particular type orseries of valves. This method is based on the simple equation:

Setpoint = System pressure + P

System Pressure = The pressure of the fluid in contact with the wetted disc area

P = The additional pressure beyond the system pressure necessary to causethe valve to lift

For a given auxiliary lifting force, a corresponding pressure differential is determined sothat the calculated setpoint is in agreement with the bench tested setpoint. A curve isthen developed from which all pressure differentials can be interpolated for a givenamount of auxiliary force (see Figure 6-1).

LIF

TIN

G F

OR

CE

DP

Figure 6-1Force vs. DP Curve for an ALD

The second school of thought determines the setpoint by calculating the seat area. Thisis done by assuming the boundary of the wetted area of the disc is at some point be-tween the ID and OD of the nozzle or disc seating surfaces. The wetted surface areashould not be assumed but should be experimentally determined. Once the assumptionof the boundary location is made, the wetted surface area is simply calculated as thearea of the circle. In this case,

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P

Lifting forceWetted surface area

=

6.4.1.3 ALD Testing Considerations

As with any type of testing, skilled personnel are the key to performing an accuratetest. While there are no special requirements in the Code specifically written for ALDtest personnel, it is important that such personnel have demonstrated a proficiency inthe use of the test equipment and this type of testing. The advantage in using equip-ment where the data is computer acquired (such as the Crosby SPVD) is that the testoperator has no effect on the test or the observed or recorded results. If contractors areused, the training requirements should be reviewed to determine the competency of theoperators. If calculations are required, they should be verified by the test supervisor. Itis also recommended that the utility provide supervision during the testing procedure.

Before testing begins, the user should obtain the calibration certificates of all test instru-ments used to perform the test or have all instruments calibrated prior to the test. Allequipment should be calibrated to standards traceable to the National Bureau of Stan-dards. Contractors should also have a QA program that requires them to notify the userabout instruments that were found to be out-of-tolerance at the end of the calibrationcycle. Whenever possible, the calibration of the contractor’s equipment should be checkedbefore and after the testing. The equipment should meet or exceed the accuracy anduncertainty requirements (if applicable) as discussed in Section 6.3.4.2 of this manual.

ALDs can not determine the “operational readiness” and/or operational characteristicsof a PRV. Therefore, valve rated lift, blowdown or freedom from cycling/chatteringcannot be demonstrated using an ALD.

Depending on the valve design and service conditions, the system pressure should notbe too close to the valve set pressure when using an ALD. High performance valvesmay experience cycling under these conditions. This caution is also valid for full lift ofthe valve using the ALD at system pressures above the valve reseat pressure. Systempressure less then 90% of set pressure is recommended, but the PRV manufacturershould be consulted if doubt exists.

Unless specificality stated by the ALD manufacturer, the use of an ALD at systempressures below 20% of set pressure should be avoided because set pressure accuracy isnot reliable. ALDs cannot determine a valve’s set pressure within acceptable set pres-sure tolerance limits at zero system pressure.

CAUTION: Attempting to lift the valve using an ALD at zero system pressure may overstress and/or damage the valve stem.

ALDs also do not recognize the differences in actual set pressure resulting from differ-ent system fluids. In order to determine the sensitivity of an ALD to various system

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fluids, the utility or manufacturer should have conducted set pressure verification testson air, steam systems. The set pressure (i.e., spring force) of the test valves should notbe altered from one test medium to the other. Once this data has been collected thevalve should be set pressure tested to verify valve actuation using only system pressureand fluid. This type of testing, depending on the system fluid, has demonstrated thatthe set pressure determined by the ALD can vary as much as five percent from the setpressure determined by pressure actuation. The reason for the variance is that thecalculated set pressure using an ALD is based on a constant seat area for a given valvedesign/orifice. The calculated set pressure will be the same irrespective of fluid tested.Thus, a correction factor for each fluid determined by actual testing must be used todetermine the correct set pressure.

6.5 Testing for Ambient Temperature Conditions

The purpose of testing for PRD ambient temperature operating environment conditionsis to establish the inservice thermal profile of the valve. Failure histories and testinghave shown that the thermal profile of a PRD must be maintained during testing both insitu and when bench tested. This data is extremely critical for valves that are required toopen within a tight tolerance band. This requires that the valve when tested have stabletemperatures at critical locations that are the same as when the valve is installed and atnormal operating temperature and pressure. The temperature of the PRD, especially thevalve bonnet, is important to a valve’s set pressure.

6.5.1 Thermal Profile Mapping

The thermal profile of any inplant installation of PRDs can depend on the number ofvalves, relative positions and different local thermal conditions. If the valves above theinlet flange and tail piping are not lagged infrared thermography (IR) can be used toestablish the specific surface temperature profile for each valve. However, if the valveand tail piping are lagged, two surface mounted thermocouples per location should bemounted on the valve inlet flange, the discharge flange, and the lower and upper springbonnet as shown in Figure 6-2.

The thermal profile should be established when the plant has stabilized at normaloperating temperature and pressure and the valve’s temperature readings have stabi-lized. Each valve location may require a different approach and waiting period to estab-lish the thermal profile. Normal full power thermal conditions are required, but fullpower operation may not be required to obtain the full power thermal environment.Each plant valve location should be surveyed to determine the required test conditions.

6.5.1.1 Infrared Thermography (IR)

IR is based on measuring the radiant thermal energy (heat) emitted from a target sur-face. This emitted heat is normally distributed over the surface and can be converted toa surface temperature map or thermogram. For a detailed discussion of IR, see theNMAC IR Guide (NP-6973 R2). The benefit of using IR to establish a safety valve’s tem-perature profile is that all of the safety valve’s exposed surface in the sensor’s field of

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view (see Figure 6-3) is measured at the same instant in time. Thus, a direct relationshipbetween the lower and upper valve surfaces can be established using the same instru-ment. No temperature sensing or recording equipment need be installed. Also, thereading can be taken at a distance from the valve that in some installations may be themost desirable from a radiation or heat stress consideration.

Cap, Screwed

Compression Screw

Bonnet

Spring

Stem

Guide

Bellows

Body

Disc Holder

Disc

Guide Pin

Nozzle

Thermocouples

Thermocouples

Figure 6-2Typical Thermocouple Placement

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MEDIUMTARGET INSTRUMENT

THE TOTAL MEASUREMENT CONDITION

PROCESSORAND

DISPLAYSENSORRADIANT ENERGY

• MEASUREMENT CATEGORIES

• The target surface

• The transmitting medium

• The measuring instrument

Figure 6-3IR Thermography

6.5.2 Temperature Profile

Each valve may have a different temperature profile so that just taking an area tempera-ture will not provide the thermal information necessary for valve testing. An example ofthis condition is shown in Table 6-2 which is the actual temperature profile of twopressurizer valves. Note that the “A” and “B” valves’ temperatures differ. The reason isthat the flange on which the “A” valve is installed has a shorter nozzle and so is closerto the pressurizer. The critical temperature appears to be the “A”-valve upper springbonnet. Subsequently, valve “A” was also reported to be the valve that always ap-peared to leak. This leakage may have been attributed to a decrease or loss in set pres-sure when installed due to temperature effects.

Table 6-2Thermal Profile for a Pressurizer Valve (˚F)

InletFlange

DischargeFlange

Tail Piece LowerSpringBonnet

UpperSpringBonnet

“A” Valve 500–501 260–277 238 347-377 230-258

“B” Valve 454-486 258-265 238 321-327 207-210

6.6 Pilot-Operated Relief Valves

A PRV that is pilot-operated and has a field test device can be tested in situ by testingthe pilot set pressure while the valve remains in service.

To test the pilot valve set pressure, an external pressure source is connected to a closedmanual field test connection (valve) and the pressure is raised above system pressure as

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shown in Figure 6-4. The field test valve is then opened to admit the external pressureto the pilot. Being higher than the system pressure, the test pressure causes a checkvalve (normally open) to close preventing test fluid from flowing back through thesystem pressure sense line into the protected system.

Vent Valve

Interconnecting Line

Shut OffValve

ExternalPressureSource

Field TestConnection

Test Gauge Pilot

Chamber A

Guide

Disc

Figure 6-4Schematic for Test Pilot Operated Relief Valves In Situ

The external test pressure to the pilot may then be increased until the pilot opens. Whenthe pilot opens, a portion of the pressure above the main valve disc will be vented(chamber A). Set pressure testing using the field test connection may or may not causethe main valve to open depending upon system pressure and/or testing technique. Forsafety reasons, it should be assumed that the main valve will open. After the set pres-sure has been verified and the pilot adjusted as necessary, the field test valve may beclosed and the external pressure source vented and disconnected.

Set pressure verification testing can validate the operational readiness of the pilot oper-ated PRV if the main valve is cycled. However, valve blowdown cannot be determined.

6.7 Setpoint Drift

The term “setpoint drift” as used for PRDs refers to the change in as-found setpoint fromthe as-left setpoint. If a deviation is noted in the first test, but subsequent valve testing,without adjusting the valve’s setpoint, coincides with the as-left setpoint valve drift hasnot actually occurred but a “setpoint variance” on the first pop of the valve has. This typeof PRD performance is not a new phenomenon, but has been a well recognized occur-rence that the National Board of Boiler and Pressure Vessel Inspectors has observed formany years. The actual setpoint of the PRD can best be determined from a series of atleast three and up to four lifts, if the first lift is not consistent with the other valve tests.The average of the acceptable three consecutive lifts should be used as the as-found or as

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left setpoint. Only after the valve’s setpoint has been determined using this methodshould any valve setpoint adjustments be made. However, if the average setpoint hasdrifted and a reason can not be determined from external inspection of the valve, consid-eration should be given to inspect the valve’s internals for wear or damage.

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7HANDLING AND SHIPPING OF SAFETYAND RELIEF VALVES

This section discusses a number of maintenance-related topics relevant to the handlingof PRDs such as safety valves, relief valves, and safety relief valves.

PRD handling, if done improperly, may affect some manufacturers’ setpoints or seattightness. Therefore, it is important to develop precise procedures for removing, clean-ing, handling, shipping, and reinstalling PRDs. Documentation of PRD testing andmaintenance results are also critical elements in a PRD maintenance program.

7.1 Handling of Safety and Relief Valves

PRVs depending upon their size, set pressure, and manufacturer’s design, could bedamaged if not handled and packaged properly for shipment. The small pilot and pilot-operated valves and small and large safety, safety relief, and relief valves with low-setpressure are especially vulnerable.

Prior to removing a valve from the system, a number of criteria should be satisfied:

• All the requirements for the valve’s removal from the system should be satisfiedincluding the identification of the relevant procedures, removal paths, and theacquisition of the certified slings and hoisting devices.

• The removal path should be identified and cleared of all interferences.

• Seismic supports should be tagged and removed, as required.

• If the valves are to be transported off-site, transport containers, for either radioactiveor nonradioactive service, and metal protective covers should be acquired andprepared prior to the removal of the PRDs. Refer to DOT 49 CFR PART 107 for designrequirements for radioactive shipping containers.

• Remove and properly store the valve insulation material.

• Properly tag electrical leads before they are removed from the valve, as applicable.

• Appropriate radiation work permit should be in effect.

• Remove instrumentation such as the linear variable differential transducer (LVDT),position indicators, accelerometers and thermocouples, as applicable.

• All lines should be drained to prevent spillage.

• QA/QC witness points should be identified as required.

7-2



• Perform necessary pre-removal inspections, i.e., valve nameplate data such as serialnumber verification, scaffolding, cleanliness, rigging, etc.

Finally, follow the instructions of the PRV manufacturer for removal.

7.1.1 Typical Rigging and Handling Instructions: Target Rock Safety and ReliefValves (Including Valve Auxiliary Equipment Removal)

The following general rigging and handling instructions are provided as a guide topreclude damage to PRD components and prevent injuries to maintenance personnel.

Cautions should be observed in the transport of the PRD and subassemblies in order toprotect the exposed flanges and bores of the safety and relief valves.

CAUTION: Remove and place the solenoid assembly of a pilot-operated relief valve in aprotective container prior to handling ANY of the PRD valve subassemblies.

CAUTION: Ensure that the technical manual used is the latest revision and acontrolled copy.

NOTE: Prior to removing the PRDs from the header, identify the piping and PRD valveinterface points with scribe marks for orientation upon reinstallation.

NOTE: Foreign material control and tool control requirements should be in effect.

• The PRD assembly should be rigged and handled as shown in Figure 7-1.

• When removing the assembly from the PRD, the pilot stage assembly should berigged and handled as shown in Figure 7-2 or 7-3.

• The base assembly should be removed from the main stage assembly in a horizontaldirection when the PRD is on the steam header as shown in Figure 7-4, or in a verti-cal direction when the PRD is in a work area as shown in Figure 7-5.

• The PRD main stage assembly should be rigged and handled as shown in Figure 7-6.

7-3



CAUTION:Remove SolenoidAssembly Prior to

Handling ValveAssembly

1 TonLift Capacity

Lifting Eyes1/2 - 13,2 Places

Note: Lift Eyes Not Supplied

Flange FaceProtective Covers

Figure 7-1Target Rock (Typical), Valve Assembly Hoisting

(Valve on Header or Work Area)

7-4



Lift VerticallyUntil Pilot Assembly

Is Clear of Baseand Studs

CAUTIONRemove SolenoidAssembly Prior to

Handling Pilot Assemblyand/or Valve Assembly

Studs

Assembly on Headeror

at Work Area

Note: Install ProtectiveCover on Flange FaceWhen Placing Valve on

Work Area Floor

Base

Studs

PilotAssembly

Air OperatorAssembly

200 Lb.Lift Capacity

Figure 7-2Target Rock (Typical), Pilot Assembly Hoisting

(Valve on Header or Work Area)

7-5



Support Lift

Strap

Drawbars (2)1-1/8 Dia. X18"Lg

Steam LineStandpipe

Horizontal(Valve on Line)

Vertical(Valve in Work Area)

CAUTIONMove along Center Line until MainSpring Force is Eliminated, Approx.150 Lbs Spring Force, Cap All OpenPorts and Flange Faces

Discharge

Lift VerticallyUntil Clear ofMain Spring

CAUTIONCap All Open Ports and Flange Faces

Figure 7-3Target Rock (Typical), Pilot Valve Hoisting

7-6



CAUTION: RemoveSolenoid Assembly Priorto Handling Valve baseAssembly

Lifting Eyes1/2 13,3 Places

NOTE: Lift Eyes Not Supplied

1 in. Dia. x 12 in. LongDrawbar, qty. 2

WithdrawAlong AxialCenterline untilClear of Springand Studs

1/4 TonLift Capacity

Figure 7-4Target Rock (Typical), Base Assembly Hoisting

(Valve on Header)

7-7



Lift Vertically until Clearof Spring and Studs

CAUTION:Remove Solenoid AssemblyPrior to Handling BaseAssembly and/or ValveAssembly

Studs



Spring

Lifting Eyes,1/2-13, 3 Places

NOTE: Lift Eyes Not Supplied

1 TonLift Capacity

Figure 7-5Target Rock (Typical), Base Assembly Hoisting

(Work Area)

7-8



Lifting Eye Bolt/Nut1-8 x 4" Long

NOTE:Eye Bolt/Nut NotSupplied

1/2 TonLift Capacity



Figure 7-6Target Rock (Typical), Main Valve Hoisting

(Work Area)

7.1.2 Typical Rigging and Handling Instructions: Consolidated, Crosby, andDresser Safety and Relief Valves

The following general rigging and handling instructions are provided as a guide to pre-clude damage to safety and relief valve components and prevent injuries to maintenancepersonnel. Some PRD designs have eyebolts, eyebolt adapters, or lifting bracket eyes onthe PRD to assist in handling. In other designs, the manufacturers may suggest locationsfor slings to be used. Still others leave this activity to the owner to use good judgement.

7-9



Whatever the case, caution should be observed in the transport of the PRD and subas-semblies to preclude damage and to protect the exposed flanges and flange faces andbores.

NOTE: The valve should never be lifted and/or carried with the lifting lever (do not removethe valve cap and lever, if applicable). On safety, safety relief, and relief valves, secure thelifting lever to the valve bonnet to prevent movement during handling and shipment (seeFigure 7-7).

NOTE: Fully assembled PRDs may weigh in excess of 1500 pounds. Be sure you knowthe weight of the valve prior to lifting so it can be rigged properly.

CAUTION: Use extreme caution when rigging the PRDs off of the mating flanges toensure that damage is not caused to the mating valve flanges and flange faces.

7.1.2.1 PRD Rigging without Eyebolts or Lifting Brackets

• The assembled safety and relief valve must be maintained in a vertical, uprightposition at all times.

• Care should be taken to prevent damage to exposed studs and mating surfaceswhen the valve or valve body is handled or stored. In addition, stud protectorsshould be used in addition to flange protectors when handling PRDs.

• Use nylon slings or other special lifting devices to move the PRD and subassemblies.Assure that the slings are free from the spindle, compression screw, spring, topspring washer and bottom spring washer, as applicable, for all lifting operations.

NOTE: Use a spreader bar to prevent the slings from creeping toward the PRD spindle.

• The PRDs should be removed from the header by wrapping a sling around thedischarge neck, then around the upper yoke structure in such a manner as to ensurethe valve is in the vertical position during the lift, i.e., not lifted in the horizontalposition (see Figure 7-7). Never lift the PRD with the lifting lever. Never hook tothe PRD spring when lifting or transporting.

• When horizontal movement is required, use the inlet or outlet flanges as the liftingpoints and exercise extreme care so as not to distort the nozzles.

• Exercise care when hoisting the PRD away from the inlet flange to prevent foreignmaterial from entering into the header or impacting the PRD flange/gasket matingsurfaces.

7-10



Release Nut

Top Lever

Drop Lever

SECURE LIFTING LEVER TOBONNET OR YOKE WITH

TAPE OR WIRE

Cap

CompressionScrew Nut

Top SpringWasher

Spring

Spindle

Yoke ("Rig Here")

CompressionRetaining Ring

Discharge Neck("Rig Here")

Disc Guide

Disc

Adjusting Ring

Drain

Adjusting Ring Pin

Seat Bushing

Base

Figure 7-7“Typical” Safety and Relief Valve Lifting Locations

7.1.2.2 PRD Rigging with Eyebolts or Lifting Bracket Eyes

• The assembled safety and relief valve should be maintained in a vertical, uprightposition at all times.

• Care should be taken to prevent damage to exposed studs and mating surfaceswhen the valve or valve body is handled or stored. Stud protectors should be usedin addition to flange protectors when handling PRDs.

• The PRD should be hoisted only by the eyebolts or lifting brackets using suitablecleats. The eyebolts or lifting bracket eyes are located to provide balanced hoisting ofthe complete PRD assembly (Figures 7-8 through 7-10). In no case should the PRDbe hoisted by any member of the auxiliary valve lifting gear linkage.

• Exercise care when hoisting the PRD away from the inlet flange to prevent foreignmaterial from entering into the header or impacting the PRD flange/gasket matingsurfaces.

7-11



Figure 7-8Typical Consolidated Electromatic Valve with Lifting Eyebolt

7-12



HoistingBracket

HoistingBracket

A A

Section A-A

Figure 7-9Typical Crosby 6R10 Safety Valve with Hoisting Bracket

7-13



Bonnet

Lifting Bracket

2-TonMinimum Hoist

Lever

1" Clearance

Cables or Slings

5/8 AnchorShackle

Figure 7-10Crosby Hoisting Arrangement for Crosby 6R10 HB-BP Safety Valve

7.1.3 PRD Cleanliness Control Instructions (at Workstation or MaintenanceShop)

The establishment of a clean work area is essential to the production of a leak-free PRDseat. The clean work area whether in a “hot shop” or open maintenance area, must befree of grease, water, solvents, and surface dirt during refurbishment activities.

Care must be exercised during the repair of safety and relief valves to assure that theminute particles of stellite are controlled and prevented from entering the reactor cool-ant system. This is very important to prevent activation during operation and therebybecoming a significant radiological hazard. When applicable, all radiation protectionrequirements should be observed to prevent area contamination.

If isopropyl alcohol is used as a cleaning agent, exercise caution to prevent the workarea from becoming airborne contaminated due to alcohol evaporation.

7.1.3.1 Generic External Cleaning Instructions Prior to Packing and Moving Valvefrom System Location

• Clean all external flange faces with an approved solvent, then rinse with demineral-ized water.

• Wipe dry with lint and chloride-free cloth or lint-free tissue paper.

• Maintain an ANSI-N45.2.2 Level “B” cleanliness for all internal parts and cover valveflange faces with a protective cover.

• Treat all debris as potentially contaminated refuse.

7-14



7.1.4 PRD StorageThe following are suggested short- and long-term storage requirements for complete PRDassemblies.

CAUTION: Inside storage in a dry, unheated warehouse environment is required for PRDsand ancillary equipment. Equipment should be stored off the floor on skids, pallets, or racks.

7.1.4.1 PRD Short-Term Storage (Less Than 12 Months)

Cover the PRD with an approved poly or plastic material. DO NOT SEAL. Leave thebottom open to avoid condensate entrapment. Place the PRD in an approved containerfor storage. ( Refer to DOT 49 CFR PART 107 for the detail requirements for storage andshipping containers.) PROPERLY packaged PRDs may be stored inside a warehousewithout inspection of its contents for a period of 12 months.

7.1.4.2 PRD Long-Term Storage (Greater Than 12 Months)

• Annual inspection is recommended for long-term storage periods in excess of 24months. PRDs scheduled for inspection should be uncrated to an extent that permitsvisual inspection of external surfaces. Care should be exercised in uncrating so thecontainers can be used again.

• Check for corrosion, contamination or other damage. If there is no visible corrosionor damage, repack the PRD as previously discussed. If any corrosion or contamina-tion is noticed, clean the PRD as prescribed in Section 7.1.3.1, dry the PRD andrepackage for long-term storage. Assure that the causes for the corrosion or contami-nation are corrected prior to returning the PRD to storage.

• Extended storage, 6 years or longer, requires detailed inspection of the PRD assem-bly and may require PRD disassembly, inspection, reassembly and retest.

7.2 PRD Shipping to an Off-Site Vendor for Inspection and Testing

A PRD consists of precision machined and fitted parts. Rough handling can sufficientlydamage or misalign the valve internals causing undesirable seat leakage or erratic opera-tion. PRDs should be shipped with a protective covering over the inlet and the outlet. Thiscovering is to prevent the entry of foreign material in the PRD. If the coverings are re-moved for inspection, they should be reinstalled as soon as possible. The protective coversshould be left on the PRD until the PRD is ready for installation into the system.

Valves should be crated or bolted to a skid with the inlet flange down on the bottomand the spindle vertical and above the inlet flange. To prevent potential misalignmentand damage to internals, never lay a safety or relief valve on its side. Safety or reliefvalves should never to subjected to sharp impact. When hoisting the PRD into positionfor installation, care should be exercised to prevent bumping steel structures or other

7-15



objects. When preparing the movement of a PRD into position, proper site riggingtechniques should be used to prevent PRD or other equipment damage.

7.2.1 PRD Preparation for Shipment

After the PRD has been removed from the system, cleaned, and the necessary protectivecovers placed on the valve, the valve can be prepared for shipment. The same care usedin handling the valve when it was removed from the system should be followed inplacing the valve in a shipping container and in its transportation. Most manufacturers’technical manuals specify recommended methods and equipment to be used for trans-porting their valves. Figures 7-11 and 7-12 (utility design) and Figure 7-13 (Crosbydesign) provide examples of typical PRD transport or storage containers. In general, thefollowing steps should be included in the owner’s shipping procedure and invokedupon the receiver of the equipment.

NOTE: The safety and relief valve should be shipped to the test facility in a shippingcontainer on a dedicated transport.

1. Perform a final radiation survey on the PRD.

2. Package the PRD for shipment according to a written packaging procedure.

3. Place the PRD in the shipping container:

(a) Verify the identity of the component prior to placement in the container.

(b) Handle the PRD and/or subassemblies in accordance with the guideline require-ments identified in the hoisting and rigging Section 7.1.1/Section 7.1.2 and anyadditional specific requirements recommended by the manufacturer.

(c) Secure the PRD and subassemblies in the shipping container as identified by theshipping procedure for the specific PRD. Some PRDs may have to be secured atthe top to prevent lateral movement and/or damage to hardware attached to thevalve.

(d) Collect the radiation protection and shipping documents and attach or enclose asrequired by the respective procedures.

(e) Load the PRD shipping container on the transport and secure.

(f) Identify the equipment in the container on the external surface by tagging orother means.

7-16



Bolted on Hinges

Cover Aluminum/16"

Aluminum Door

Gasket

Quick Release PinCord

Figure 7-11Typical Utility Design PRD Transport/Storage Container

7-17



Mount hinges from top here

36"

60"

2 1/2"

36"

31"

Figure 7-12Typical Utility Design PRD Transport/Storage Container

7-18



NOTES1. Construction of super-

structure consists ofnominal, 1x4's and 1/2thk. CDX Plywood.

2. Line all interior surfaceswith PPP-B-1055, Cl.L-2B Asphaltic Kraft. Alljoints to be glued andnailed.

3. Block and brace as re-quired to immobilizevalve while superstruc-ture is being fabricated

36-1/8"

Stencil OtherEnd: "Do Not LiftThis End. Off-Center Load"

3"

78"

48"

Nail superstructure to skid. Nailspacing approximately 2-1/2".After nailing superstructure toskid, band around girth withheavy duty, nailless,steel strapping intwo (2) places.

FORK FROMTHIS END

UP

DO NOTLIFT

FROMTOP

VALVE REMOVEDFOR CLARITY

CAUTION

OFF CENTER

LOAD

UP

Figure 7-13Typical Crosby PRD Packing Crate Construction for

Crosby Pressurizer and MSSVs

7.2.2 PRD Valve Receipt (Typical)

This section addresses typical vendor requirements for safety and relief valve receipt,inspection and handling activities at the test facility.

7.2.2.1 PRD Removal from the Shipping Container

1. Verify external markings on container to shipping documents.

2. Unpack the PRD assembly and separately packaged air operator per utility andmanufacturer uncrating instructions, as applicable. The PRD and subassembliesshould still be secured to the container.

3. Verify the PRD name plate data against the shipping documents prior to removingthe PRD from the transport.

7-19



4. Lift the PRD from container per the requirements identified in the hoisting andrigging Section␣ 7.1.1/Section 7.1.2 or as directed in the uncrating instructions afterthe initial radiation survey has been completed and as directed by the radiation protec-tion technician.

7.2.2.2 PRD Receipt Inspection

An initial external visual inspection of the PRD should be conducted to determine theas-found condition of the valve. The following points should be addressed:

• Verify that no transport damage to the PRD has occurred.

• Ensure that the PRD has been shipped properly and in the vertical position.

• Ensure that the lockwired seals for applicable locations are still intact.

• Verify that all hardware has been received with the PRD.

• Check the condition of the cotter pins.

• Check the condition of the PRD inlet and outlet flanges.

• The PRDs nameplate and serial number.

• Verify the packing list for individual items such as subassemblies.

• Report any unacceptable conditions to the responsible party.

7.2.2.3 PRD Storage

If the PRD is not to be tested for a prolonged period, the PRD and its componentsshould be stored in a controlled storage area. See Section 7.1.4 for applicable storagerequirements.

7.2.3 PRD Packaging and Return Shipment Preparation

This section addresses typical vendor requirements for return shipment of the PRD tothe utility.

7.2.3.1 PRD Preparation for Return Shipment

1. Verify nameplate information on the valve to confirm it is the component to beshipped.

2. Perform a final PRD radiation surveys as required.

3. Package the PRD for return shipment to the owner according to the test facility’spackaging requirements that have been approved by the owner or as directed by thetest facility’s radiation protection technician.

7.2.3.2 PRD Placement in Shipping Container

1. Verify nameplate information on the valve to confirm it is the component to beshipped.

7-20



2. Handle the PRD and subassemblies according to the requirements identified in thehoisting and rigging Section 7.1.1/ Section 7.1.2 or as specified in the owner’s proce-dure.

3. Secure the PRD and subassemblies in the PRD shipping container as identified bythe shipping procedure for the PRD.

4. Collect all the PRD testing and shipping documents and attach or enclose as re-quired by the respective procedures.

5. Seal the container and identify the contents on the external side of the container.

6. Load the PRD shipping container on the transport and secure.

7.2.4 PRD Documentation and Procedures

The safety and relief valve vendor manual provides the necessary instructions for theinstallation and maintenance of the safety and relief valves. The manual will typicallycontain the following information:

• Design features

• Theory of operation

• Storage and handling precautions

• Terminology

• Principles of operation

• Specific corrective maintenance techniques and specialty

• Field settings or adjustments

• Disassembly, assembly, and repair guidance

• Troubleshooting recommendations

• Replacement spare parts

Vendor manuals are typically specific to a PRD model and/or serial number sequence.These requirements are significant for safety related components and of importance fornon-safety related PRDs. Good vendor documentation provides a record of exactlywhat was supplied and received. Information that is fundamental to each PRD installa-tion is the inlet and outlet flange bolting and gasket configurations. This documentationshould include the use of checklists and procedures that identify to utility personnelcritical components to ensure adequate quality control can be maintained. It also pro-vides the first step in the history from when the PRD arrives on site and is inspected.Vendor manuals must be controlled and updated regularly to assure the requisiteservice bulletin, etc., are incorporated.

Utility Purchase Order and/or Procedures

The utility procurement and inventory departments are responsible for ordering andstoring safety and relief valves including spare parts. The initial basis for purchase order

7-21



begins with the original component design specification. This design specification providesthe necessary information to purchase replacement PRD and spare parts while maintainingdesign configuration control. The procurement department should have internal proce-dures that identify a programmatic method to be used when purchasing replacementcomponents, service, and spare parts. ASME Section III class components may require anaddition level of documentation to support QA requirements (Section 7.2.5).

Vendor Procedures

Utility maintenance procedures are developed and maintained through vendor-sup-plied procedures and vendor manual updates/bulletins. In most cases, the vendorprocedures cannot be used directly by the utility. This requires that the vendor manualand procedures be reviewed and evaluated to develop specific utility procedures. Theutility-generated procedures should then be reviewed by the vendor for completenessand accuracy. This should be accomplished initially and after performing componentimprovements or changing test methods.

Operating Experience

Industry and internal operating experience is gathered by each utility and forwarded tothe maintenance and technical support ISI department personnel responsible for safetyand relief valves. This information should be evaluated to determine if there existssimilar operational likeness to the utility’s specific PRD types. If there is a commonrelationship, then the responsible department should take action to determine the safetysignificance and identification of necessary corrective actions.

Utility maintenance and/or program support departments monitor safety-related safetyand relief valve performance on selected non-safety PRD. The extent that non-safety-related PRD are monitored is unique to each utility. There is little cost benefit informa-tion that suggests that the non-safety-related PRDs should be monitored. This maychange in the future when the USNRC Maintenance Rule goes into effect in 1996. Theneach utility may develop a monitoring program to trend the performance of these PRDs.If the utility develops this program early there will be a savings in the number of non-safety-related PRD failures and the combined implementation of the USNRC Mainte-nance Rule.

7.2.5 PRD QA Requirements

General Discussion

Based on the regulatory, Code, and insurance requirements, the maintenance of pres-surizer and MSSVs must be governed by a QA program consistent with the require-ments of Appendix B of 10CFR50, ANSI N45.2, ANSI/ASME NQA-1 or Section III ofthe ASME Boiler and Pressure Vessel Code.

Specific quality assurance interfaces with maintenance include “hold points” or “witnesspoints” for critical refurbishment steps such as ring settings, setpoint tests, and NDEexamination. The utility’s QA program should ensure that these particular hold pointsare incorporated into the PRD maintenance procedures.

7-22



The utility’s QA program should also ensure that both maintenance personnel and QCinspectors are properly trained in PRV maintenance and inspection. Adequate trainingprograms should include written instruction and hands-on training.

Vendor Reports

Vendor documentation and procedures provide a record of exactly what was suppliedand received. This documentation should include checklists and utility receipt inspec-tion procedures to enable personnel adequate QC for incoming materials. It also pro-vides the first step in the history of the part from when it arrives on site and is in-spected. Vendor records should include the following:

• Vendor’s QA inspection record with actual critical dimension verifications and sign-offs

• PRD assembly drawings identifying purchase order number, part name(s) andnumber(s), serial number(s), Code references, overall dimensions and tolerances,handling requirements, and shelf life

• Certificate of Compliance to the purchase order requirements

• Certified material test reports including a report of mechanical properties andchemical analysis as required by the specific ASME Code to which the valve ismanufactured.

• Bill of materials listing the part(s) supplied and material designation, special pro-cesses including statement of heat treatment and weld processes, required examina-tions and any special notes and requirements

• Record of all dispositioned non-conformance identified during manufacturing orinspection with the owner’s approval

• Vendor manual, vendor manual revisions, or supplements applicable to the part(s)

• NDE reports including visual, liquid penetrant, ultrasonic, and radiographic asapplicable

• Certificate holder’s data report for nuclear components, parts and appurtenances,when the original order was for an NV stamped PRV.

Utility Reports

The utility-generated documentation provides the PRV’s history trail from transferred,pre-service inspected and tested, installed, reworked, reinstalled and removed from thesystem. Safety-related PRVs should be tracked by a maintenance technical supportgroup responsible for the PRD testing and off-site vendor test report review and evalua-tion.

Recordkeeping

Detailed records of safety and relief valve design, operation, and maintenance areessential for a successful PRD maintenance program. The records should be maintainedby the appropriate system engineer, maintenance engineer, or ISI engineer.

7-23



It is desirable to have the records in a centralized location that allows ready access bymaintenance, technical support, and engineering personnel. A file for each PRD isrecommended to provide a collection point for maintenance records, failure root causeevaluations, vendor contact information, and relevant industry reports and notifica-tions. These records ultimately become a PRD equipment history record invaluable toperforming root cause failure analysis.

System Files

As detailed recordkeeping is an essential part of the PRD maintenance program, systemfiles are the individual files for each component. The purpose of a detailed record is todevelop a specific equipment history. This information is useful to the maintenancesupervisor or technical support engineer. If PRD performance degrades, the informationcollected in these files can be helpful in determining PM schedules and also provide abasis for PRD refurbishment.

8-1



8MAINTENANCE AND PERFORMANCE TRENDING

8.1 Predictive Maintenance and Inspection

Predictive Maintenance programs for PRVs are different than programs for activecomponents such as pumps. PRVs are passive by design and only activate under abnor-mal system operating conditions. Passive components such as PRVs, therefore, requirecondition-directed tasks normally found by active monitoring, testing, or inspections.Several methods can be used to predict the condition of PRVs. The condition-directedmethods listed in the following subsections when effectively used can determine theoperational status of safety valves. If the predictive techniques identify a PRV operatingimproperly, the corrective maintenance guidance provided by the PRV manufactureralong with the special maintenance considerations described in Section 8.3 through 8.11of this guide can be used to repair the valve.

8.1.1 Parts Control

Throughout the PRV disassembly, extreme care should be exercised to ensure that allcomponent parts remain with their specific valve. Under no circumstances shouldcomponent parts be exchanged from one valve to another. Table 8-1 lists the basicprinciples of parts control. The variables that influence parts control are:

Valve Size: Size will dictate the type of control that can be used on specific valves.Smaller valves and their disassembled components may be contained in their entirety insuitable tote pans (plastic preferred) or similar containers. The pan(s) can then be tem-porarily tagged with the valve ID number or another appropriate method of identifica-tion. As the PRV increases in size it will be necessary to adjust the method by whichcontrol is accomplished. Smaller parts may still be placed in tote pans, but larger partswill have to be tagged and kept with the tote pans on a pallet or similar container and inone area (e.g., tote pans with smaller parts placed on a pallet or receptacle holding thelarger parts (body/bonnet, etc.).

Lead Time for Replacement Parts: Sometimes during valve repair, replacement parts arenot readily available. In this case, the valve should be held in a satisfactory holding areauntil parts can be procured. The holding area and its proximity to the work area shouldbe determined by the anticipated lead time for replacement part(s). In the event leadtime for repair parts is long, it is recommended that the specific disassembled valve beplaced in a temporary controlled storage area. This will help eliminate the possibility ofconfusion, parts loss, or inadvertent switching of parts from taking place. Considerationshould also be given to possibly performing a loose assembly of the valve with appro-priate tagging to identify its status in the repair cycle. This type of loose assembly will

8-2



assure that the valve internals do not get misplaced. It may also be appropriate to main-tain an inventory of parts to be used in the repair, based on the valve manufacturer’srecommendation or valve repair history.

Shop Versus In-Line Repair: Shop repair is usually structured into a set pattern. Thisstructured approach allows for more control of parts due to the surrounding environ-ment. In-line repair requires a great deal more flexibility due to its nature and tech-niques that must be used to accomplish the repair process.

System for Valve Repair: One valve is repaired at a time. This type of repair will reducethe need for skidding or handling of valve parts unless temporary storage is required.In the event that more than one valve is repaired at a time, parts control becomes essen-tial. The system for parts control that is implemented should be specifically defined.

Table 8 -1Basic Principles of Parts Control

1. Identification of the specific valve

2. Segregation of parts

3. Verification of parts serialization to utility records (seeNote A)

4. Containment of the disassembled valve

5. Mobility of contained parts (if necessary)

6. Damage prevention of internal components (e.g.protecting valve seats)

Note A: Controlled parts for ASME Section III Class 1, 2 or 3Pressure Relief Valves are serialized and recorded onthe ASME NV-1 form.

8.1.2 Visual Inspection

A visual examination of the internal pieces of a PRV can be conducted to determine thecondition of a part, a component, or a valve’s seat or disc surface condition. The exami-nation should include looking for conditions such as wear, corrosion, erosion, cracks, orphysical damage on the surfaces of the part or component. The use of an illuminatedmagnifying glass, inspection mirror, metallurgical examination, and boroscope may beappropriate. The visual guidelines given in this section may seem obvious and notimportant, but many valve failures can be avoided by properly conducted visual exami-nations.

The visual examination can also be used to locate evidence of leakage from pressureretaining components or abnormal leakage from other components. In addition, thevisual examination can be conducted to determine the general mechanical and struc-

8-3



tural conditions of components and their supports, such as the presence of loose parts,internal and external debris, abnormal corrosion products, wear, erosion, corrosion, andthe loss of integrity at bolted or welded connections.

Clean surface conditions are necessary for valid interpretations of erosion, cracks, andother defects. A clean surface is defined as one which is free of loose foreign material suchas rust, scale, welding flux or spatter, excessive grease or oil, dirt, loose and flaking paint,etc. Cleaning may be performed with the use of a stainless steel wire brush, demineral-ized water, isopropyl alcohol, or an approved solvent with clean rags. Only stainless steelbrushes, not previously used on other materials, should be used on stainless steel.

Evaluation Criteria for Pressure-Retaining Bolting and Flange Surfaces

The following conditions or indications are normally considered unacceptable:

• Cracks.

• Galling, stripping, or cross threading, unless isolated to an unused portion of theitem.

• Corrosion, arc strikes, or mechanical damage that reduces the cross-sectional area by5% on studs or bolts that are normally under tension when installed.

• Corrosion, arc strikes, or mechanical damage of all surfaces. This is considered to bedetrimental to the function of the component in which the bolting or weld is in-stalled.

• Threads that are not engaged for the full length of the thread in the nut. Bolts andstuds should extend completely through nuts. If this cannot be accomplished, thestud or bolt should be replaced.

Evaluation Criteria for Safety Valve Internal Pressure Boundary Surfaces

The following conditions or indications may be unacceptable and require an engineer-ing evaluation to determine acceptability:

• Cracks, other than light superficial surface crazing which occurs in the thin hardsurface skin of castings

• Erosion, corrosion, and wear that infringes on the minimum wall thickness or isconsidered to be detrimental to the component’s function

• Loose parts

• Foreign material

• Structural distortion or displacement of parts to the extent that component functionmay be impaired

• Bent or degraded parts

Any abnormal wear or surface conditions should be documented with photographswhenever possible

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8.1.3 Acoustic Monitoring

Acoustic monitoring is typically used to detect leakage from safety valves where thedischarge is common to other safety valves or PRVs in a non-accessible space duringplant operation. Monitoring equipment can be portable or locally installed at each valveor along piping runs to provide remote indication to monitor safety valve leakage.Permanently installed equipment can be used to determine when and which safetyvalve has lifted during a plant transient or test.

Acoustic systems have been used to monitor leakage past pilot valve seats at some BWRplants. PWR plants have used acoustic monitoring on PRVs where valve stem move-ment cannot be observed. Acoustic monitoring equipment has also been used to mea-sure sound disturbances in the discharge pipe. The selection of equipment to use isapplication dependent. Personnel who specialize in acoustical engineering should beused to develop the monitoring techniques and type of equipment to use.

Acoustic systems used for PRV leak detection consist of sensors, signal processors, anddisplay units. The typical device uses either accelerometers or sensors to convert acous-tic energy in the 10 kHz to 100 kHz range into an electrical signal. These signals canthen be displayed on oscilloscopes, spectrum analyzers, RMS voltmeters, and X-Yplotters. Some systems use a computer for analysis by first storing the information andthen downloading to the computer.

There are two main methods of comparison that can be used for detecting a leakingPRV:

Baseline Comparison: In this method, a baseline reading of the PRV is established when itis certain the PRV is not leaking and is in normal operating condition. Then a reading istaken periodically at the same plant conditions and compared to the baseline readings.

Comparison: In this method, the PRV’s acoustic data is compared with the baseline of asimilar PRV. The PRV used for comparison should be similar in construction, design,and application. The best selection is an identical PRV in the same type of service withthe same acoustical background levels.

8.1.4 Temperature Monitoring

Temperature monitoring equipment that can be used for PRV condition monitoringincludes permanently installed resistance temperature detectors (RTDs) or portablepyrometers. In addition, these devices can be used during PRV testing to determine thecondition of a PRV both before and after scheduled maintenance. Section 6.5 of theguide provides information on obtaining temperature profiles and how they can beused for valve testing.

Safety valve leakage that has been attributed to the PRV temperature profile used dur-ing testing was covered in Section 6. As discussed, a temperature profile needs to bedeveloped for each individual PRV. A manufacturer’s test procedure that includestemperature values is adequate for initial testing, but a plant-specific temperature

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profile is needed to ensure that correct PRV setpoints are maintained. It has been notedduring the testing of safety valves that as a valve’s bonnet temperature increases, thevalve’s actual set pressure decreases and leakage may occur. The opposite is also true inthat as the valve’s temperature decreases, the setpoint increases. This change in setpressure will not be identified during testing at a laboratory if the same incorrect tem-perature profile used to originally set the valve is used to retest the valve.

Several factors can contribute to changes in a valve’s temperature profile:

• Valve inlet piping length can directly affect valve temperature. The length of thecooler pipe separating a PRV from its pressure source is critical to the temperaturesthe valve sees during operation.

• Valve insulation can effect valve performance. Insulation used during testing mustbe the same as installed in the plant.

• Air flow around the valve during plant operation can effect a valve’s temperature.Operations personnel should understand that during plant operation any changes inventilation in the area of the safety valves can effect their setpoints. Also, mainte-nance personnel should understand that any forced ventilation used for personnelaccess can effect the valve’s setpoint. This type of maintenance induced failure is notdetected until an overpressure event has occurred and may not even be identified asthe failure cause when an event has occurred.

• Quench tank temperature can effect valve temperature. If a valve’s quench tanktemperature is at or near the saturation temperature then this could effectivelymaintain an elevated temperature in the safety valve.

The above factors are the reason why safety valve thermal profiles are important. Theyare also plant specific and should be used in testing. This includes set pressure testingwith steam and leakage testing with nitrogen. In order to accurately set the valves andto ensure the tightest valves during power operations, the valves should be set with thetemperature of the critical areas maintained to the specific thermal profile.

IR uses specialized photographic equipment to measure and record absolute and rela-tive temperatures of surfaces. See Section 6.0 and NMAC Document #NP-6973R2 fordetailed information about the use of thermography. IR surveys (infrared inspections),should be used to trend and analyze the performance of PRVs. Baseline surveys shouldbe scheduled every five years and prior to scheduled valve testing if used to determinethe PRV thermal profile. This permits proper testing to identify required maintenanceprior to unexpected failures.

If insulation is not present, surveys can be used to determine the PRV thermal profile asdescribed in Section 6 or can be used to detect PRV leakage. Color thermography equip-ment will give the best results for leakage testing. “Before and after” IR surveys shouldbe used as a method for determining the adequacy or effectiveness of seat leakagecorrective actions.

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Temperature profiles should be correlated with the acoustic baseline discussed in Sec-tion 8.1.3. By trending these condition-directed tasks, PRV leakage can effectively bedetected and repaired.

8.2 Trending Safety and Relief Valve Performance and Maintenance History

The trending of safety and relief valve performance and maintenance histories is a keyelement in solving and preventing safety valve problems. It will also assist in the main-tenance and repair work that may be required for any particular valve, predict spareparts requirements and finally may assist in the identification of the root cause of aproblem valve. An aggressive trending program as outlined below provides a complete,accurate and easily accessible record of valve performance. With this type of record, anyanomaly in the valve’s performance is easily identified and can be corrected.

8.2.1 Safety and Safety Relief Valve Performance and Maintenance Trending

PRV performance trending should be performed under each of the following conditions:

• Normal operating conditions

• Transient conditions

• Overpressure conditions

• Test conditions

It is under these conditions that the safety and relief valves must be relied upon toperform one of their design functions.

All safety and relief valves should be included in the maintenance, testing and trendingprograms because these valves perform an important personnel safety function. This istypically not the case. In most nuclear plants, inspection and maintenance activities areusually focused on valves that are installed in systems that perform an importantnuclear safety function. If a neglected safety or relief valve is required to relieve in re-sponse to an overpressure event and fails, the possibility for a pipe rupture exists. Thismay result in many consequences including personnel injury.

Performance trending of safety and relief valves is most effective when the trended datais maintained in an organized log or filing system. This record should contain the sametype of data in the same format for each valve that is being trended to facilitate reviewand evaluation. The person responsible for initiating the trending log must first deter-mine what data will be trended, how frequently the data is obtained, the data format,and the method for evaluating the data. In addition, the final presentation of the resultsmust be considered when designing the trend log.

The data to be trended for inservice valves should include:

• Seat leakage

• Body-to-bonnet leakage

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• Premature lift

• Failure to lift

• Service time before the valve failure

• Thermal profile data

• Acoustic monitoring data

The data to be trended for valves in test should include:

• Seat leakage

• Out of tolerance lift

• Premature lift

• Failure to lift

• Ring settings (if applicable)

Developing and trending the thermal profile of a safety valve establishes the stabletemperatures at specific locations on the valve when installed in the system and thesystem is at normal operating temperature and pressure. This thermal profile effects theset pressure of the safety valve which, in turn, affects the seat tightness of the valve.

Maintenance usually occurs on safety and relief valves as a result of an inservice failure,test failure, or a problem identified during inspection. The maintenance practices rec-ommended in this section include comprehensive maintenance and inspection activitiesthe results of which are recorded on maintenance data sheets.

Typical data that should be trended related to the maintenance of safety and reliefvalves include:

• Wear characteristics

• Degraded or deficient material conditions

• Incorrect “as-found” data

• Foreign material or corrosion

This data is recorded in the trend log each time a work order is written for any safety orrelief valve in the trending program. In addition, a schedule should be developed thatinspects and tests safety and relief valves on a predetermined frequency.

The frequency for inspection and testing of safety and relief valves should be commen-surate with the function of the application. The ASME Code defines the test frequencyfor valves that are included in the inservice test (IST) program and NUREG-1482. Theseare valves identified in the plant’s final safety analysis report as having a safety functionthat prevents or mitigates the consequences of an accident. Typically, these valves aretested on a staggered frequency such that each valve is tested at least every five years.For valves that are not in the IST program, the inspection and test frequency should bedetermined based on several factors including valve performance history, safety func-

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tion, and consequence of failure. The frequency can be established based on these crite-ria and adjusted as a performance record is established. Valves with good performancecan be inspected and tested on a reduced frequency and the bad performers can bescheduled for inspection and test on a more frequent basis with an eye toward identify-ing causes and plans for corrective actions.

The trending log should record the data and any relevant information, such as valve tagID, work order number, and the date. Each sheet can include maintenance, inspection,or test results performed per a work order. The key performance and maintenance datashould be extracted from the data sheets and included on the log to permit effectivetrending, and the complete data sheets from the work package should be attached to thelog to complete the reference.

The individual trend log sheets do not provide additional data that is very useful.However, when the sheets are compiled over a long period of time, the performanceand maintenance histories become evident. This trended data should be used to adjustthe maintenance and test schedules to effectively apply resources to the “bad actors.”

8.2.2 NPRDS Trending and Failure Codes

The NPRDS (Nuclear Plant Reliability Data System) is a computer database maintainedby the INPO (Institute of Nuclear Power Operations) for use by the nuclear industry.The purpose of the database is to enhance the operations of nuclear plants by analysis ofcomponent performance history. The database contains records of selected componentsfor each nuclear plant in the United States. These records contain specific informationabout each component of interest indicating the manufacturer, component characteris-tics, and the record of reported failures.

The NPRDS database is a useful tool to supplement the trending efforts describedabove. Periodic evaluations of safety and relief valve failure data as compared to indus-try failure data can be performed and corrective actions taken if adverse trends areidentified. Searches of industry data for reliability, failures, and the effect on plantoperation can also be performed.

For the NPRDS database to be a useful tool to utilities and the industry, the reporting offailures must be standardized so that meaningful comparisons of data can be made. INPOhas provided a standardized categorization and classification system for the reporting offailures. Briefly, it consists of four basic categories to which all failure causes are attrib-uted. The categories are mechanical, electrical/electronic, adjustment related, and human.Cause codes are identified for each type of failure cause. For example, setpoint drift,material defect, incorrect procedure, etc. Some cause codes may appear in more than onecategory. It is recommended that utilities formalize the categorization of failures consis-tent with the INPO NPRDS program, report all component failures, and perform plantand industry trending as an enhancement to the maintenance program.

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8.2.3 Trending and Analysis of Adverse Conditions

The analysis of the trended data should be comprehensive enough to detect subtle andnot so subtle trends. To accomplish this, the trending should not only occur for a par-ticular valve in a particular system, but should also occur for the same valve type indifferent systems and different valve types in the same system. Adverse trends such asthe following should be identified:

• Repetitive failures or degradation of the same PRV or similar types of PRVs

• Recurring failures or degradation in certain systems

• Recurring failures or degradation in PRVs located in certain application (e.g., pumpdischarge)

This type of trending can lead to solutions of problems related to a particular PRV typeor a particular system. For example, if a particular PRV type has a high failure rate thatis consistent for different systems, it may indicate a problem with the design of the PRV.If a particular PRV or many different types of PRVs experience a high failure rate in thesame system, this might indicate a chemistry problem or a problem in the way thesystem is designed or operated.

If trending indicates poor safety valve performance, abnormal degradation or impend-ing valve failure, then immediate corrective action should be taken, as appropriate, andthe safety valve program should be revised to address the root cause of concern.

• When applicable, design reviews should be performed to determine the adequacy ofvalves for specific applications and design changes initiated as necessary.

• Technical specification changes should also be considered when a valve is failing itssetpoint acceptance criteria on a regular basis, but the criteria is overly restrictive forthe application. Many times, a setpoint acceptance criteria of ±1% is specified whenthe actual system requirements would warrant a larger tolerance range. There arenot many safety valves that consistently produce at a setpoint within ±1% of thenameplate setpoint over a period of time.

The trending program should not be established for the sole purpose of trending. Itshould be used to provide good data that may be used in future valve maintenancework. Further, this data should be used in a thorough analysis process to obtain the rootcause of a problem and correct it.

8.3 Preventive Maintenance (PM) and Inspection

Planned maintenance is the cost-effective application of a preplanned, organized set ofintegrated maintenance activities that will significantly contribute to inherently reliablePRV operations. Each maintenance action should be preplanned to ensure that thedesigned safety and reliability levels of the PRV are maintained. The PM action shouldidentify and restore degraded conditions as they occur and obtain the necessary infor-mation for taking corrective action on valves where the desired reliability is notachieved. This type of PRV maintenance program encompasses the total maintenance

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triad consisting of preventive, predictive, and corrective actions. The first two (preven-tive and predictive) are supportive in that they prevent aging effects from leading to theloss of important valve functions through the timely identification of degrading condi-tions. They are more condition-directed than time-directed and can be integrated into atrue planned maintenance program.

Corrective maintenance activities should be used as a feedback to the planned programto enhance actions that prevent future failures. This section describes the typical actionsnecessary to inspect and correct PRV failure causes as described in Section 5. However,because many of the PRV failure causes are not PRV specific, separate sections for eachPRV manufacturer type is not presented. This section only provides an overview of thecritical areas of preventive and corrective maintenance of a PRV .

The maintenance and inspection of PRVs has in the past not been accomplished by theowner or a repair organization. Scheduled planned maintenance can prevent most ofthe aging failures as discussed in Section 5. This section of the guide is not meant toreplace the specific PRV manufacturer’s maintenance manual but to highlight somespecific maintenance actions that can be used to reduce many of the failure causes listedin Table 5.1.

8.3.1 Valve External

8.3.1.1 Identification

The first inspection step of any PRV maintenance action is the positive identificationfrom its nameplate of the valve that is to be repaired. Identification should include thefollowing:

• Valve ID number

• Serial number

• Verification of manufacturer

• Verification of valve size and type

• Verification of valve set pressure

• Verification of valve ASME Code Stamp (UV, NV) and Class (1, 2 or 3 for ASME“NV” stamped valves only)

• Verification of valve location ID (if applicable)

All of the above information should agree with the valve’s documentation. In the caseof an ASME Section III valve, the documentation should include an “NV-1” form, aserialization record of the valve. The stamped set pressure should correspond with themanufacturer’s tag and also be consistent with the plant maintenance informationprovided for the specific valve. There should be an appropriate tag affixed to the valvenear the original manufacturer’s tag if any changes were made to the valve since it wasoriginally manufactured, such as new valve set pressure, capacity, and blowdown. Theoriginal manufacturer’s tag should have information crossed out, but still be legible. In

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the case of valves where the lift set pressure is also stamped on the discharge flange, theset pressure should be deleted with the old lift set pressure still legible, in the samemanner as the tag above. Verification of the lift set pressure is essential in the event thatthe manufacturer’s tag has been altered or lost and there is no appropriate reset infor-mation affixed to the valve (set pressure is crossed out or illegible).

In the event the lift set pressure cannot be positively identified, there are several meth-ods that may be used to obtain the PRV lift setpoint:

• From the PRV maintenance history (old test report or stored valve maintenance data)

• Verification through the valve manufacturer in conjunction with a traceable valveserial number

• From the top of the valve discharge flange (some manufacturers die stamp set pres-sure, valve type, and valve serial number on the discharge flange)

8.3.1.2 External Visual Inspection

Before the disassembly, several preliminary actions can be performed to help in themaintenance process. The first preliminary action is visual inspection that can identifyseveral specific PRV problems. Points of inspection should include the following:

Seals/Previous Repair Information: Inspection of valve safety seals (usually lead) should beperformed to ensure the valve has not been tampered with (e.g., lift setpoint and ringpins) since its last repair or as-left condition. Any discrepancies such as broken or missingseals should be duly noted along with any previous repair information (affixed metal tag).Repair information may include the following: date of last repair, lift set pressure, repairorganization, mechanic identification, VR stamping, and/or valve capacity.

Gasket Sealing Surfaces: In closed bonnet designs, sealing surfaces should be examinedfor signs of leakage (e.g., corrosion, erosion, or removal of paint in affected area). Gasketsurfaces should include body/bonnet, cap, gag plug, and ring pins. Also included insealing surfaces are the nozzle/body seal if a full nozzle valve design is used.

Lever Assembly Function (if present): Lever assemblies are of two basic designs, open orpacked, as shown in Figure 8-1. Open lever design will need only to exhibit the abilityof the lever to engage the lift nut. This will require freedom of lever movement andclearance between the lift nut and lever. Some valves use a lift washer and lock nutdesign. This configuration requires lever clearance (the distance between the lift lever atrest and the lift washer). With the lock nut configuration present there is a chance forthe lock nut to become disengaged allowing the lift washer to work its way down thestem and jam on the lift lever. This can cause the valve to leak or to be in a permanentpartially open position. The packed lever should also engage the lift washer. Due todesign configuration, the lift washer and lock nut (if present) cannot be inspected visu-ally for clearance, but can be checked by lifting the lever to at least a 45˚ angle. A packedlever may also be found in a frozen position (no movement possible). This is usually anindication that contamination (e.g., steam, water, etc.) is present in the cap area creatingcorrosion in the lifting gear assembly.

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O-Ring

Drive Pin

Cam Shaft

Bushing

Lever

Packed Cap

Lock nut

ReleaseNut

Packed Lever

Open Lever

Open Lever Cap

Lock Nut

Release Nut

Lever Pin

Lifting Lever

Cap Screw

Stem

Figure 8-1Lever Assembly Design

Inlet and Outlet Flange Faces: The inlet and outlet flange faces (or valve nozzle flangeface) should be inspected for damage and the condition noted. If the valve body is astudded construction, the studs and nuts should be inspected for damage. For weldedinlet and outlet valves, the condition of the weld end should also be noted.

Discharge (if accessible): Visual inspection of the internal components through the valveoutlet may reveal signs of prior valve leakage. Indicators of leakage can mean severecorrosion or erosion of the valve seat and require part replacement.

Test Results: PRV test results can provide valuable information that may be usd to ana-lyze adverse valve condition. Table 8-2 lists information that should be used to deter-mine PRV maintenance action.

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Table 8-2Test Results Useful for Determining PRV Maintenance

1. As-found lift setpoint of the valve (high, low, or OK)

2. External valve leakage present

3. Severe seat leakage present; e.g., seat leakage is sosevere that a valve lift setpoint cannot be established(leaked too bad to pop)

4. Failure to open at +10% of valve stamped lift setpressure (no manual lift lever assist)

5. Failure to open at +10% of valve stamped lift setpressure (with manual lift lever assist)

6. Lift lever assembly frozen

7. Erratic lift set pressure results

8. Leaking bellows

8.3.2 Valve Internals

8.3.2.1 Disassembly Methods

With the external visual inspection of the valve complete, documentation on the valvereviewed and verified, and the “as-received” tests for set pressure, etc., completed, thenext step is to disassemble the valve and perform an internal visual inspection. Thesteps of this process are:

1. Have available the necessary documents on the valve.

2. Have available the manufacturer’s instruction manual or plant documentation onthe specific valve.

3. Review to confirm that all necessary standard and special tooling is available.

4. Serialization record and verification. As stated in Paragraph 8.3.1, valves that havebeen manufactured to ASME Section III will have all pressure retaining parts serial-ized. During disassembly and assembly processes, verification of the serial numbersshould be performed. If parts are changed, a record of the new serial number shouldbe made in the records by the utility or repair agency.

With the above reviews complete and equipment available, the disassembly process canbegin.

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Most manufacturer’s instruction manuals recommend two types of disassemblyprocedures:

• Disassembly retaining the spring compression (termed “jack and lap”)

• Complete disassembly without retaining spring compression

The jack and lap procedure is generally used on spring-loaded PRVs that are 2-1/2- to 8-inch inlet sizes with high set pressure spring loads (pressurizer safety valves, MSSVs forPWR and BWR plants). The procedure is used when the valve repair activities areanticipated to be minimal such as “seat lapping only.”

Complete disassembly is used on all sizes of PRVs. Generally, all valves 2-1/2 inch andsmaller are completely disassembled. Valves of larger sizes may be jacked and lapped.

Valve manufacturers provide specific information on when either method of disassem-bly should be used and will rent or sell equipment that will assist the technician who isperforming the disassembly.

CAUTION: Personnel are cautioned that both procedures (jack and lap and/or completedisassembly) must be performed to the manufacturer’s recommendations, or damage to thevalve pieces can result.

In Section 8.6, each type of disassembly operation is described and illustrated.

8.3.2.2 Securing the PRV for Maintenance

The first step that should be performed before repair of any PRV is the securing of thePRV in a fixed upright position. The important point here is to prevent damage to thePRV during maintenance. The valve size and configuration will dictate the method thatcan be employed. Several methods that may be used are:

• A vise mounted on a bench or the floor

• Bolting or clamping to a secure test flange (stand)

• Positioning the discharge flange in a V channel angle iron setup

• Any other variation or adaptation of the above that will secure the valve in a fixedupright position

NOTE: Care must be taken not to damage valve inlet flange sealing surfaces when secur-ing the valve for maintenance.

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8.3.2.3 Match Marking

Before disassembly, the PRV should be match marked to ensure that the body andbonnet are reassembled exactly in the position they were prior to disassembly. This is aone-time procedure. Place the match mark on the center back portion of the valve whenpossible. In the case of multiple existing match marks, the following should be used toreestablish alignment. First, remove all previous markings from the bonnet and bodyusing a surface grinder or similar tool. Prior alignment can be obtained from an identi-cal type of valve that is present in the repair shop, plant, or storage. If this approach isnot possible, it may be necessary to contact the valve manufacturer for specific valvealignment. Crosby and Consolidated valves have the bonnet vent holes to the front(above the outlet flange) and Farris valves have vent hole to the back. This vent locationwill assist the positioning of closed bonnet valves. Upon reestablishing alignment, oneset of permanent match marks should be made on the flanges as shown in Figure 8-2.

Low stress die stamping a valve accomplishes match marking and permanently identi-fies the specific valve. Match marking is not required for valves where components arethreaded and reassembly requires a locking technique.

MSSV 23

MSSV 23Match Marks

Figure 8-2Match Marks

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8.3.2.4 Cap and Lever Assemblies

Removal of a lever assembly, packed lever, or plain cap is a fairly straightforwardprocedure. During such a removal process, visual inspection should be made to confirmthat assembly was correct.

8.3.2.5 Confirmation of Ring Settings

If the valve is of a design that has adjustable rings (nozzle ring and guide or adjustingring), the as-found locations of these rings should be verified at this point in the disas-sembly process.

It is important that the method used to confirm ring setting is in accordance with thevalve manufacturer’s procedures. A single valve manufacturer may use differentprocedures depending upon the valve style and/or type, and each manufacturer has amethod that is not common to any other valve manufacturer.

NOTE: Review ring settings for valves in Sections 8.7 through 8-11.

The as-found settings of these rings should be compared to the as-left settings based onthe specific valve records. If they are not identical, an investigation as to the cause forthe difference should be made and corrective action immediately taken.

8.3.2.6 Compression Screw/Adjusting Bolt

If the valve is completely disassembled, match marking and measuring the position ofthe top of the adjusting bolt to the bonnet provides an approximate location to reposi-tion the bolt to achieve the same compression when the valve is reassembled.

Larger (high pressure) compression screws normally have a hex head construction tofacilitate removal. Some smaller compression screws have two milled flats. All com-pression screws are of right-hand thread design (clockwise to install or increase pres-sure and counter clockwise to remove or decrease pressure). Compression screw designvaries with the valve design. High-pressure valves (such as Consolidated types 2700,31700, 3700 and Crosby types HA and HC) will typically have thrust bearings incorpo-rated in their design as shown in Figure 8-3. Thrust bearings allow for the compressionscrew to transmit the power load of the spring to the disc assembly without the occur-rence of severe galling between the compression screw bearing point and the upperspring washer bearing point. Valves without thrust bearings have the compressionscrew bearing point directly engaging the upper spring washer. If the valve is com-pletely disassembled, the threads on both the compression screw and the bonnet/yokeshould be thoroughly cleaned and inspected as described next.

Inspect the Compression Screw. This should include all bearing surfaces (especially if nothrust bearing is used in the design) for galling, out of round or any surface damagethat may adversely affect freedom of movement. Inspection of the compression screw

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threads is very important when there is any difficulty in removal (e.g., frozen in placeand takes excess force to remove usually resulting in thread damage).

Damage to one or two threads with moderate tearing can be remedied. The end resultmust be freedom of movement, the ability to screw the compression screw into thebonnet/yoke with no binding (without lubricant). If this cannot be accomplished, thenfurther inspection of the threads is required, and the valve manufacturer should becontacted to confirm the thread size and recommended repairs.

Yoke

ThrustBearing

Cage

LubricateBearing

Lubricate

Spring Washer

CompressionScrew

ThrustBearing

CompressionScrew Adaptor

AligningWasher

Figure 8-3Typical Thrust Bearing Design

8.3.2.7 Studs and Nuts

Removal of body/bonnet nuts is a straightforward process that may be accomplished inthe easiest manner available. During reassembly the tightening of the body nuts shouldbe done with a torque wrench if recommended values are available.

CAUTION: The spring must be free of tension when removing the bonnet nuts. Seriouspersonal injury or damaged parts may result if the spring remains under tension when thebonnet is removed.

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Inspection of the studs and nuts should include the following:

• Look for thread damage on either the nut or the stud. The stud/nut should havefreedom of movement (the ability of the nut to be moved up or down the stud byhand). Some thread damage can be corrected through thread chasing or taps, butmust be addressed (corrected or replaced) or damage will increase during reassem-bly (nut may seize causing breakage or severe irreparable damage).

• Look for erosion of exposed studs between bonnet and body (if present by valvedesign). If erosion is present, stud(s) replacement is recommended.

8.3.2.8 Bonnet/Yoke Removal and Inspection

Removal of a closed bonnet should be accomplished by lifting it in a straight verticalplane. It is very important to keep the bonnet in a straight vertical plane so as not tomomentarily bind/catch the spindle/spring assembly. If binding is experienced, thereis a chance of seat damage by some of the components above slipping out of the bonnetand falling into the valve. Size and weight will dictate whether the bonnet can be re-moved manually or require mechanical assistance. If a mechanical assisted lift of thebonnet is necessary, the bonnet may have threaded holes provided (by design) to alloweye bolts or similar lift assist devices to be installed.

Designing a permanent lifting device is recommended. In the case of a larger closedbonnet, it is helpful to limit the number of times the bonnet has to be handled (lifted).Closed bonnets may have recessed or raised body gasket surfaces. Recessed gasketsurfaces can be laid on a flat surface since there is little or no chance of physical damage.When placing a raised gasket surface bonnet in a resting position, it should be placed ona surface that will not damage the sealing surface (e.g., wood, cardboard, etc.).

Removal of an open bonnet or yoke design usually requires less effort due to the factthat it is physically less demanding to sling for mechanical lifting. Some designs requirethe spring assembly to be lifted at the same time the open bonnet is being lifted over thespindle. Care must be taken to keep the bonnet in a perfectly vertical position so as notto allow the spindle (stem) to bind/catch the bonnet or the spring washer ID. If thisoccurs, the stem along with the disc assembly could possibly fall back into the valve andcause unnecessary seat damage.

Visual inspection should include all gasket surfaces and threads for the adjusting bolt.For closed bonnet designs, the area and threads of studs and nuts that affix the cap tothe bonnet should also be inspected.

8.3.2.9 Spring Assembly (Spring and Washer) Removal and Inspection

Removal of the spring assembly from a valve is accomplished by vertically raising itfrom the spindle. Size will dictate the method of removal; smaller spring assembliesmay be manually removed as a unit. Larger assemblies may have to be removed byseparate components parts (e.g., top spring washer, then spring, and last the bottomspring washer). In the case of larger spring assemblies where mechanical lift is

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necessary, care must be exercised to not inadvertently lift the spindle/disc assembly. Ifthis occurs, there is a possibility of the spindle/disc assembly dropping back into thevalve causing unnecessary seat damage. See Table 8-3 for inspection points.

CAUTION: Each spring washer (top and bottom) in most manufactures’ valves is customfitted to the spring. During disassembly, identify to which spring end the washer is fitted. Thiswill assist and assure correct placement of the spring during reassembly.

Table 8-3Spring Assembly Inspection

1. Look for the presence of uneven coil spacing (collapsed).

This condition may cause repeated lift setpoint drift (low) orfailure to obtain desired lift setpoint.

2. Look for coil erosion or metal decay. Severity inconjunction with past valve performance (lift setpoint drifthigh or low) will determine if replacement is required.

3. Measure the spring standing free height and compare itwith design length.

4. Look for cracked or broken spring.

5. Look for the presence of lateral bending (spring is notperpendicular to top or bottom machined flats).

The spring washers are important in that they transmit the power of the spring to thedisc assembly. When spring replacement is necessary it is imperative that the newspring has been properly fit with a new set of washers by the manufacturer.

Another critical area of the spring washer is its bearing point surface: the lower springwasher bearing point contacts the spindle bearing point while the upper spring washerbearing point contacts the compression screw bearing point (unless thrust bearing designis present). Inspection of spring washers should primarily focus on the bearing points andthe surface the spring rests on. Bearing points should be free of galling and show a uni-form concentric surface that has been in contact with the mating part. The surface onwhich the spring rests should be flat and free of erosion or any physical damage. Somepitting and corrosion is acceptable in noncritical areas of the spring washers.

Thrust bearings are incorporated in some upper spring washer designs (see Figure 8-3).They should have freedom of movement or the ability to be restored to this condition.In the event the bearings are frozen and freedom of motion cannot be obtained bycleaning and lubrication, the thrust bearings should be replaced.

8-20



8.3.2.10 Nozzle Ring/Lower Ring

Removal of the nozzle ring should be accomplished in conjunction with obtaining anozzle ring location measurement (in cases where the specific valve manufacturer usesthis method or manufacturer ring setting or past maintenance history is not provided forassembly purposes). The nozzle ring can be removed after taking the nozzle ring lock pinfrom the valve body. The nozzle ring is removed by turning in a counter-clockwise mo-tion until the threads disengage. It is imperative that the nozzle ring be held firmly whileremoving it from the valve body. Failure to do so may result in the nozzle ring beingdropped causing severe damage of the nozzle seat, and require machining. If a nozzlering is found in a frozen state, the ring must be freed prior to valve repair.

After removal, the nozzle ring should be cleaned (especially threads) so that a properinspection can be made. The nozzle ring should be examined for the following types ofdamage:

Missing Teeth/Notches: This condition can adversely effect proper setting of nozzle ring ifmissing notches are located at the lock-in position (e.g., -3 notches). Replacement will de-pend on the ability to properly set (lock in) the nozzle ring to its appropriate measurement.

Steam Cuts: This condition requires replacement due to the impact on the huddlingchamber and valve performance (blowdown/simmering).

Out-of-Round: If the nozzle ring cannot move freely up and down the nozzle because ofout-of-roundness, replacement is recommended.

Thread Damage: If the nozzle ring cannot move freely up and down the nozzle becauseof thread damage, replacement is recommended.

8.3.2.11 Disc or Disc Assembly Removal and Inspection

The typical disc assembly, shown in Figure 8-4, is commonly removed from a valve inconjunction with the spindle (stem) as a unit. Care must be exercised during removal notto damage the disc or nozzle seat. When removing the disc assembly, note the degree ofrestriction that is present (e.g., the disc assembly should be free from any restriction thatlimits smooth/clean removal from the valve guiding system). Degree of restriction mayvary as described in Table 8-4 and have a number of causes and effects on the PRV.

Design characteristics will dictate the disc assembly removal process. There are a vari-ety of basic designs used for disc retention. Some are:

• Threaded (Consolidated design shown in Figure 8-4 disc and spindle)

• Cotter pin (Crosby HS, HC and JO) for disc insert (see Figure 8-17)

• Retainer clip (Consolidated 1900 Series, Crosby HS, HC and JO) for spindle or discinsert (see Figure 8-5)

A review of each specific manufacturer’s instruction manual will provide instructionsfor the removal procedure.

8-21



Disc HolderDiscCollar

Rock Gap Disc

CotterPin

Figure 8-4Typical Disc Assembly

Table 8-4Disc Removal Restrictions, Causes, and Effects

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8-22



Guide

Disc Holder

Retainer Ring

Disc

Nozzle

Figure 8-5Typical Retainer Ring for Disc Insert

If, in the cotter pin retention design, the pin is distorted or broken, replacement is neces-sary. With replacement it is important that the new pin’s material be of equal grade asthe old (e.g., never replace a stainless steel pin with carbon steel). It is also importantthat the pin be of proper length so as not to contact the guiding surface.

After disassembly, the parts (disc, disc holder, retainer mechanism) should be cleanedso a proper inspection can be made. Cleaning may be accomplished in stages duringdisassembly or in entirety after the valve is completely disassembled.

The disc holder is a critical component in the internal structure of a PRV and should beinspected accordingly. It works in conjunction with the valve guiding system and itsfailure to meet acceptable criteria will result in valve failures. Table 8-5 lists majorfailures that may result due to component conditions.

8-23



Table 8-5Disc Holder Failure Causes and Effect on PRV Performance

Inspection Point Condition Possible Result

Guiding surface Pitting Corrosion buildup which may result in set point drift (high),seat leakage, or failure to lift

Guiding surface Galling Failure to lift due to lockup of disc holder in guide

Top Steam cuts Adversely affect huddling chamber/valve performancecharacteristics (e.g., blowdown—simmer)

Bleed holes(if applicable)

Plugged Adversely affect blowdown characteristics of valve

Threads Damage(torn or stripped)

Will not allow proper engagement of disc/disc holderbearing points which could result in seat leakage

Bearing points Galling or pitting Seat leakage due to improper engagement of bearingpoints

Corrective action should be implemented for some of the “conditions” listed above (e.g.,bearing points, threads, bleed holes) to make them acceptable. In the case of the discholder guiding surface, only minor cleanup is allowed (e.g., use of crocus paper orsimilar while turning in a lathe). Use of coarse paper for cleanup is not recommendeddue to the possibility of reducing the diameter of the disc holder, causing a looser fit(clearance) of the disc holder to the guide. In the case of steam cuts, there is no correc-tive action that may be taken. Replacement of the disc holder is recommended if there isdamage in either of the above areas. Bearing points of the disc/disc holder should beinspected for damage or wear. Transmission of the spring force occurs through thebearing points. Therefore, it is critical that they be free of damage. Look for galling,erosion, pitting, and any metal distortion in the bearing contact areas and mushroomingor peening of the bearing point.

Machining and Lapping: Discs are evaluated for repairs in the following manner. Theseverity of damage combined with allowable disc tolerance determines whether ma-chining can be performed before lapping. Most manufacturers have machining toler-ances and minimum tolerances. It is important to understand the difference between thetwo concepts. Machining tolerance is a measurement that the manufacturer requires thecomponent part (disc) to have after it has been machined. Minimum tolerances are di-mensions for the component part (disc) that must not be exceeded per manufacturerspecifications to be a useable piece that can be installed in a valve. In most valves, discinserts cannot be machined and only the seat should be lapped.

Tolerances are established by manufacturers for each specific valve to ensure optimumperformance. Exceeding tolerances may result in unsatisfactory valve performance (e.g.,failure to meet blowdown requirements, presence of simmer, or chattering). Before

8-24



machining and lapping, it is important that machining tolerances for the specific disc beknown so that proper machining can take place.

Figure 8-6 shows a typical Crosby disc insert (without a flexi-disc seat) and identifiessome of the critical dimensions of the part. Beyond this, there are other geometricalshapes that are also critical and controlled in manufacturing.

Thermal or flexi-discs require lapping only (if damage permits) for refurbishment. Therewill typically be an outside relief minimum tolerance that will determine the ability ofthe disc to be reused. If the outside relief is below the minimum allowable tolerance, thedisc should be discarded and replaced.

In all cases, the owner should follow the manufacturer’s instructions for part reuse andrefurbishment.

CD-Min D-Original

A Dia.

Seating Surface

B Dia.

Figure 8-6Typical Disc Tolerances

8.3.2.12 Nozzle Design Types Removal and Inspection

Nozzle designs vary from one manufacturer to the next. Basic designs of nozzles are asfollows:

• Full, threaded and removable

• Semi, threaded and removable

• Semi, welded in valve body

• Semi, pressed and removable

Prior to reviewing nozzle designs, it is important to note that the nozzle seat in conjunc-tion with the disc seat form the primary pressure containment boundary in a PRV.

8-25



Proper repair of a damaged seat is the first step toward ensuring that a PRV will per-form to an acceptable standard. Nozzle seats have critical dimensions as do the discseats. The nozzle tolerances are established by the manufacturer to ensure optimumvalve performance. This is the allowance between machining tolerance and minimumtolerance as explained in the disc section. The nozzle seat should be inspected afterappropriate cleaning. Measurements of the nozzle seat should be taken and recorded.Lapping should be done if it can be accomplished within the minimum tolerance con-straints. If tolerances cannot be held, then machining of the nozzle is recommended.When tolerances are not met or exceeded, valve performance will suffer. Improperevaluation and repair of a nozzle seat may result in failure and/or adverse performanceof the valve. Figure 8-7 shows typical critical dimensions of a valve nozzle, and Table 8-6 identifies effects on valve performance.

CB

AReliefStep

Nozzle

Figure 8-7Typical Critical Dimension for Nozzle Seat

8-26



Table 8-6Typical Improper Nozzle Tolerance Effects on Valve Performance and Tightness

1. Blowdown: failure to meet required blowdown for set pressure of the PRV.This may cause the blowdown to violate the operating pressure boundarycreating reseat failure.

2. Simmer: premature release of media prior to lift. May develop intopermanent leakage.

3. Chatter: serious condition where rapid opening and closing of a valveoccurs. Can result in a number of adverse conditions: leakage, setpointdrift low, damage to internal component parts, or reseat failure.

4. Tightness: valve seat leakage.

Full Nozzle: A full nozzle can be removed from the valve with a special tool available fromthe manufacturer. It can also be removed from the valve body as shown in Figure 8-8. Itsdesign makes it part of the inlet connection of the valve and is threaded into the valvebody at the inlet from the outside. Factors determining whether the nozzle is to be re-moved from the body depend on the specific valve and plant procedures (see Table 8-7).

Table 8-7Full Nozzle Removal Criteria

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The full-nozzle design requires additional points of inspection (beyond seat inspection):the inlet and the nozzle body threads (when nozzle is removed). The inlet can be re-paired using standard flange refurbishment. The nozzle body threads, in conjunctionwith the body threads, allow the nozzle to be returned to a locking position in the valvebody. Thread damage should be corrected to allow reinstallation and lockup of thenozzle in the valve body.

8-27



Semi Nozzle (Threaded/Removable): This nozzle is designed to be internally threaded intothe valve from the top of the body and locked on a sealing surface or shoulder. Leakagecan occur through the threads and/or sealing surface. Any evidence of leakage or theactual testing of the nozzle (bushing) may be used for evaluation. Cost factors (replace-ment value) should dictate if leakage will be corrected. Leakage can be corrected in thefollowing manner:

• Removal of the nozzle bushing with proper tooling

• Proper cleaning of nozzle and body threads

• Application of thread sealant

• Reinstallation of nozzle bushing and curing of sealant, if required

If there is damage present in the body threads or on the sealing shoulder (erosion/steam cuts caused by severe leakage), replacement of the valve is recommended.

Semi Nozzle (Welded): The semi-nozzle design has a bushing that is internally insertedinto the valve body and welded in place by the manufacturer. It may become necessaryto replace the nozzle bushing due to severe seat damage. Replacement of a weldednozzle bushing should only be performed by the valve manufacturer.

Semi Nozzle (Pressed): There are two versions of this type of construction: 1) an internallypressed (permanent) nozzle in the valve body in conjunction with a body seal, and 2) afree-standing nozzle that rests in an internal recess of the valve body. Typically, thistype of valve has a back seat (O-ring or similar soft seal) to isolate inlet pressure. Anysoft seal of this nature should be replaced during each repair.

Base

Nozzle

8'-10' Long Rodor Heavy Pipe

3 Jaw Chuck

Chuck Stand

ProtectNozzle Seat

CAUTION: The Nozzle OD and Flange Face Must BeProtected to Preclude Damage to These Surfaces.

Figure 8-8Full-Nozzle Removal

8-28



8.3.2.13 Stem/Spindle Inspection

The stem/spindle transmits the power of the spring to the disc assembly. Transmissionof this power must occur in a uniform manner that allows even distribution of thespring force to the valve seats. Failure of uniform distribution to occur may result inadverse valve performance (e.g., leakage/internal binding of component parts). Acommon cause for bending of the spindle is overgagging of the valve. However, ther-mal expansion of the spindle while gagged can also cause bending.

Inspection should involve checking the stem/spindle for total indicated runout (TIR).This is accomplished in the following manner. The spindle is placed in a vertical posi-tion with the ball end in a fixed pocket and the top end in a fixed V block as shown inFigure 8-9. A dial indicator is then positioned to contact the spring bearing point surface“C”. The stem is then rotated and a reading taken from the dial indicator. The amountof allowable TIR will vary according to valve size, type, and manufacturer’s allowance(typically <0.007"). If the runout is beyond allowable limits, the stem will need to bestraightened. Straightening of the stem can be accomplished by either of the following:

• V blocks in conjunction with a padded press

• Between centers in a lathe using a rubber mallet

Generally, the standard stem/spindle construction consists of two bearing points: springwasher contact surface and disc/disc holder pocket contact surface. There can, however,be additional critical areas depending upon the valve design, so manufacturer’s standardsshould always be followed. The bearing points are critical to the transmission process(spring force to seats) and should not be overlooked. Bearing point conditions that mustbe addressed are galling, erosion, uneven wear, and bearing band-width.

Some spindle designs also incorporate a lift stop (such as Consolidated 31700, 3700, and2700). The lift stop is set by the manufacturer and controls the measured lift a valve mayattain. If the lift stop is removed, it is imperative that it be properly set upon reinstalla-tion. Improper setting may result in the failure of a valve to attain full lift and its ratedcapacity. The lift stop can be set by adjustment (up or down) on the threaded portion ofthe spindle provided for it. The spindle along with the disc assembly are lowered intothe valve and the cover plate affixed. A measurement is then taken from a fixed point(usually the top of the compression screw to the top of the spindle) and recorded. Thespindle is then manually lifted until the lift stop engages the cover plate (spring assem-bly is absent during the procedure). A second measurement is taken at the fixed pointand recorded. The difference between the two measurements is the lift of the valve. Thelift stop is adjusted accordingly to meet lift requirements (including any allowances forthermal expansion per the manufacture’s specifications) and pinned.

Other parts that may be attached to a valve spindle as part of the valve internals are apiston (backup to a bellows), a disc collar (see Figure 8-4) used to retain the disc holder,spindle and insert as an assembly, and an overlap collar used in the Consolidated(Dresser) backpressure closing design, to mention a few. The owner, with the help ofthe valve manufacturer and the instruction manual, must address the type of inspec-tions required for each design and incorporate them into the maintenance procedure.

8-29



SECTION XX

A

A

45˚C

X X

B

Figure 8-9Stem Inspection

8-30



8.3.2.14 Guide Inspection

A guide or guiding system is incorporated in all PRVs as part of their basic design.Guiding systems can be classified as either top-guided or bottom-guided, spindle-guided,or disc/disc-holder-guided. Top-guided has the guiding system incorporated above thenozzle seat. Bottom-guided has the guiding system below the nozzle seat. The guide isdefined as the mechanism used to concentrically locate the disc/disc holder so as tocreate positive seating interface between the disc and nozzle seat.

Bottom guides have their guiding system built into the nozzle bore (nozzle bore andguide are one and the same). A typical disc holder/top guided system is shown inFigure 8-10. This system incorporates a component part that is independent from thevalve body. The guide rests in a recess provided for it in the valve body, or it rests ontop of the body and aligns itself with the body bore. It is imperative that the guide restproperly in its designed seating surface provided by the manufacturer.

Cap

Cap Gasket

Spring Washer

BonnetSpring

Spring Washer

Body

Guide

Guide Ring

Disc WithBushing

Nozzle Ring

Nozzle

Adjusting Bolt

Adjusting BoltLock Nut

Gaskets

SpindleSpindleLock ClipGuide RingSet Screw

Gaskets

Nozzle RingSet Screw

Set ScrewPin

Set Screw Rod

Figure 8-10Typical Disc/Top Guided System

The guiding surface of the guide is designed so that it runs at a 90˚ angle to the valveseats. Any damage (e.g., raised surface caused by dropping or improper disassembly)that would prohibit the guide from seating properly on the provided surface will resultin seat leakage. The guiding surface must be inspected for damage and/or wear. Ad-verse conditions that may be found in the guiding system are described in Table 8-8.

A typical spindle guided system is shown in Figure 8-11. In this guiding design, thespindle is guided by a guide that is located in the valve body. The spindle also guidesthe disc holder to assure proper disc seat to nozzle seat alignment and contact.

8-31



Any of the conditions shown in Table 8-8 will usually warrant replacement of the guide.Adverse conditions will usually coincide with conditions found on the disc holder and/or spindle.

Table 8-8Guiding System Troubleshooting Guide

Condition Possible Causes Effects on Valve Performance

Out-of-round Vibration in the systemthat may cause wear ofthe guide

1. Leakage2. Valve may hangup after opening (low reseat pressure)3. Erratic test results

Galling 1. Valve chatter2. Guide out of tolerance3. Dirt in guiding surfaces

1. Set point drift (usually high) due to binding ofguiding surface

2. Leakage3. Failure to reseat at correct pressure

Corrosion 1. Aging2. Seat leakage

1. Binding in the guiding surface that may result inset point drift (high)

2. If caused by seat leakage, may become worseand result in part failure

Steam cuts Seat leakage Poor valve performance, blowdown requirements,or improper lift

Guides with guide rings incorporated into their design should be inspected for thefollowing:

• Freedom of assembly and disassembly. Should be able to be adjustable freely on theguide threads.

• Free of steam cuts.

If there is a guide ring stop pin present in the valve body, it is important that the guidering be adjusted so that it does not contact the stop. If the guide assembly is placed inthe valve and the guide ring is contacting the stop (ring is down too far), valve leakagewill occur.

8-32



Screwed Cap

Compression Screw

Bonnet

Spring

Stem

Guide

Bellows

Body

Disc Holder

Guide Pin

Nozzle

Disc

Vent Opening

Figure 8-11Typical Spindle-Guided Bellows Valve and Bellows Testing

8.3.2.15 Bellows Inspection

Inspect the bonnet cavity/spring assembly and the bellows internally for any signs ofleakage (e.g., corrosion or any contaminant that would indicate such).

Pressurize the valve body with air through the outlet to a pressure value recommendedby the valve manufacturer, as shown in Figure 8-11. In the bonnet vent, place a leakdetecting solution or a plug with a tube and the tube outlet submerged in water. Ifleakage is present in the bellows, bubbles will occur in the water.

CAUTION: When this test is performed, all bonnet leak paths should be sealed.

If the bellows leaks, it should be replaced. If the gasket leaks, it should be replaced. Ifdisassembly is required, the PRVs technical manual should be carefully followed. Ifthere are any questions about the removal process, a resolution with the manufacturershould be obtained prior to the maintenance being performed. The bellows is a verydelicate component and must be handled accordingly. Special tooling is usually re-quired and may be obtained through the valve manufacturer.

8-33



8.4 Generic Corrective Maintenance

8.4.1 Lapping

8.4.1.1 Lapping Valve Seating Surfaces

This section describes the general methods used for renewing the disc and nozzle seat.The objective of this section is to provide a basic overview of valve seat lapping that canresult in a reliable, leak-tight valve.

In the repair of PRVs, there is one maintenance activity that is common to all valves:lapping of the seats. The pre- and post-cleaning and lapping operation in all cases is thesame except for the compounds, vehicles, and lapping blocks used to obtain the desiredsurface finish and optical flatness (for flat-seated valves). Therefore, prior to performingthe lapping operation, the following should be reviewed and confirmed:

• Review the manufacturer’s procedures.

• Confirm lapping blocks/tools are optically flat and in a ready-to-use condition.

• Determine (based on manufacturer’s recommendations) the type of compounds (gritsize) and vehicle to be used (e.g., compound diamond or aluminum oxide, grit sizefrom 100 to 1000).

• Confirm that seats to be lapped conform to and have adequate material to conformto manufacturer’s dimensions after lapping.

• Determine if the seat can be refurbished by lapping or remachining. If not, replace-ment is required.

8.4.1.2 Cleaning—Prior to Lapping

General cleaning of the nozzle bore, threads, and disc should be completed prior to seatrenewal (lapping). If possible, the nozzle should be removed from the valve body so itcan be systematically cleaned in its entirety (i.e., bore, inlet, nozzle ring threads, andbase threads). Nozzle removal will also produce a better environment for lapping,taking seat measurements, and performing inspections. Cleanliness in the nozzle bore,inlet (gasket surface), and the disc seating area is imperative for quality safety valverepair. Lack of cleanliness in these areas can result in contamination of the lappingcompound, causing unsatisfactory results (i.e., poor seat surface finish followed byfailure of seat tightness specifications).

The purpose of cleaning is to remove all physical contamination. Physical contamina-tion is the presence of any dislodged material that results in failure of the seating sur-face. An area normally requiring cleaning is the outside relief (step) of the nozzle be-cause there is a tendency for corrosion particles to bond to the relief step (Figure 8-12).

8-34



Nozzle

Relief Step

Figure 8-12Nozzle Relief Step

8.4.1.3 Precautionary Measures Prior to Seat Refinishing

Seat refinishing is the last step performed on the disc and nozzle prior to reassembly.Precautionary measures that should be taken are:

• Check spindle threads in conjunction with disc insert threads (if applicable). There isa tendency for the lead threads to present some difficulty in starting. If this is thecase, clean up the thread or threads causing the problem. The disc should also spinonto the spindle freely with minimal effort on the contact surface and be free of anygalling.

• Check cotter pin holes and their alignment with disc insert and disc holder (if appli-cable). Corrosion can build up in these areas causing the cotter pins to bind whenthey are being inserted. Make sure that these holes are free and clear of any corro-sion or foreign matter.

• Make sure that the nozzle ring can move freely on the nozzle. The ring should bechecked without any form of lubricant on it. Corrective action may include: chasingthreads (manually and lathe threading), wire brushing and/or cleaning, use ofcoarse grade compound, correcting out of round ring, or replacement of the nozzlering.

• Make sure that there is no binding of the disc in the disc holder and that the disc isfree to rock. Binding occurs due to corrosion build up or damage in the guidingareas on either the disc or disc holder. Binding should be corrected by using a finefile or abrasive paper on the area of concern.

• Take any measurements that are required pertaining to the “as-left” condition of thedisc and nozzle (see Figures 8-6 and 8-7). The radial dimensions do not requirereverification because the lapping cannot change the dimensions of the seating area(i.e., ID and OD of the disc and nozzle). At this stage of the repair process, thesedimensions have already been determined.

8-35



8.4.1.4 Inspection for Seat Condition

Inspection of the seating area is conducted to determine at what level the lapping pro-cess should be started. Listed below are common seating area conditions along withsuggested repair actions to return the valve to an operating condition.

• Minor visible imperfections are described as having no apparent physical damage tothe seating area. When the seating area contains only minor imperfections, seatrenewal can be accomplished by using lapping compound only.

• Minor seat damages consist of small cuts, scratches and pitting that do not run all theway across the seating surface. Seat repair will require minimal effort to restore theseating area to an acceptable level. Usually a coarse lapping compound or mediumgrit abrasive paper (320 grit) can remove damage at this level. When visual inspec-tion indicates the damage has been removed, the seat can then be lapped to thedesired finish. Sometimes it may appear the damage of the seating area was re-moved only to find out, during the use of the compound, that some damage stillexists. In this case, return to the first step in the procedure and repeat the processuntil the desired results are obtained.

• Major seat damages include pronounced cuts, scratches, scoring, and pitting that runall the way across the seating area. Damage removal at this level will require signifi-cantly more effort than minor damage, and seating area relief tolerances may alsocompound the repair process. When dimensions are not available, the valve manu-facturer should be contacted. Damage of this nature can be removed by using abra-sive paper (120, 150, 180 grit size) or by machining. Inspection of the damaged areasshould be performed periodically during the lapping process to determine when thephysical damage has been totally removed. After removal of the damage to the seat,relief measurements and any other critical measurement required by the manufac-turer (e.g., nozzle overall height) should be taken to ensure that minimum toleranceshave not been exceeded.

The nozzle seat height dimensions are critical because, if too much material is re-moved from this interface, the critical dimensions controlling valve performance canbe affected (see Table 8-6). Critical dimensions on the disc (see Figure 8-6) can alsoaffect its fit in the disc holder and the valve’s performance. When the safety valve isreassembled with an excessive amount of material removed from the disc/seatinterface, the spring is extended to make up the axial dimension of the removedmaterial. This extended spring results in a lower lift setpoint. For certain valve types,manufacturers will recommend a jack and lap procedure without retesting the valve.Therefore, the allowable amount of material that may be removed from the disc/seat interface without affecting the lift setpoint should be obtained from the manu-facturer. This dimension should be tracked to ensure that cumulative lapping opera-tions do not adversely affect the lift setpoint of the valve.

At this point (if relief step tolerances are acceptable, see Figure 8-7) a medium-gradecompound can be used. A coarse-grade compound may also be acceptable as astarting point. In either case, the final objective is to graduate to a polishing-gradecompound to obtain a quality finish on the seating surfaces. As in the previous

8-36



sections, it may be necessary to repeat some or all the steps in the procedure toobtain satisfactory results.

• Wire drawings describe serious damage of the seating area. Wire-drawn areas of theseating surfaces are created by the continuous leakage of the fluid medium across anisolated cross section of the seating surface. Due to damage severity, either machin-ing or seat replacement will be necessary.

• Stress cracks are cracks in the seating area that usually radiate from the ID out andrun perpendicular to the circular configuration of the seat. Initial inspection does notalways reveal the presence of stress cracks, and damage can be difficult to repair.Cracks tend to be more easily observed during the final stages of the lapping process(the use of fine or polishing grades of compound). Stress cracks will have varyingdegrees of severity and thus require varying degrees of effort to remove. Theyshould be evaluated by some type of NDE examination method. Complete removalof damage of this nature is imperative due to the tendency of the cracks to fissureand open when heated with pressure applied. Removal of the damaged areas can beperformed using the same techniques used in 8.4.1.3 and 8.4.1.4 above. If the crackspersist, it may become necessary to machine the damaged seating area or evenreplace the damaged seat to correct the problem.

8.4.1.5 Lapping Operation

A conservative approach is recommended for the lapping process. The most conserva-tive option is to use a lapping compound (polishing grade/high grade number). Themost liberal option is the use of abrasive paper (low grade number). It is easier to goback in the progression and use coarser compounds than it is to start with a coarsecompound that removes excessive metal.

There are no stringent rules that govern the process of lapping with compound. Thereare, however, principles and concepts that affect the final outcome. Lapping requires acombination of skill, patience, diligence, practice, and touch. Other factors involved arechoosing:

• The proper size and type of lapping tool

• The proper grit size (fine, medium or coarse) (see Table 8-9)

• Proper hardness or type of abrasive (aluminum oxide or diamond)

• Lapping time

• Pressure applied to the part being lapped

CAUTION: For a flat seat safety valve, never lap the disc seat against the nozzle seat.

8-37



Table 8-9Lapping Compounds

Abrasive Grit Size AverageMicronSize

Description Manufacturer Trade Name orEquivalent

Silicon carbide 320 31 Medium coarse U.S. Products Number 2F Crystolon

Silicon carbide 400 22 Medium U.S. Products Number 3F Crystolon

Silicon carbide 600 16 Fine U.S. Products Number A-600Crystolon

Hard alumina orAluminum oxide

900 9 Polish U.S. Products Number 38-900-A

Information on diamond lapping compounds should be obtained from the valve manufacturer fordiamond compound type, and when and where the compounds should be used.

When lapping, it is important to use the lapping (block) tool recommended by themanufacturer, which will cover the seating area at all times during the procedure butdoes not excessively overhang the seating area. This is important in smaller sized orifices.The use of a lap that is too large creates a tendency to rock the lap while performing theprocedure. This will create unsatisfactory results such as the following:

• Unacceptable Seat Finish: fine scratches on the polished seating surfaces.

• A Seat That Is Not Flat: high or low areas in the seating surfaces. This is representa-tive of a seating surface that has areas that are highly polished, accompanied byareas that have a dull lustre.

• Loss of the Perpendicular Relationship: between the seats and the valve spindle and disc.

The most common type of surface finish measurement for seat flatness is the use ofoptical flats with a monochromatic light. This method represents the most accuratemethod of checking surface flatness. Optical flats use light bands to measure surfaceflatness with one band equal to 11.6 millionths of an inch. Interpretations of light bandreadings are based upon a point of contact on circular pieces. Because this type of mea-surement is difficult to perform in the field with portable equipment, the degree offlatness is obtained by a transfer process. That is, verification of the optical flatness ofthe lapping block prior to use causes the valve seat to be suitably flat to achieve valvetightness. Obviously, to assure that this transfer process is correct, the following guide-lines should be used:

• Use a different lapping block for different grade compounds.

• Clean the surface being lapped and the lapping block frequently during the processto remove contaminated compounds.

• Use a newly reconditioned lapping block for the final lapping operation.

• Recondition the lapping block frequently (see note).*

8-38



NOTE: Lapping blocks (ring) can be reconditioned on a lapping machine or on a recondi-tioning lapping plate as shown in Figure 8-13. The reconditioning plate is made of a specialgrade of annealed cast iron (as are the lapping blocks). It is machined and lapped flat onone side and has small squares. It is on this side that the lapping block is reconditionedusing the appropriate compound and moving the lap as shown in Figure 8-13.

Lapping Plate Lap Ring BLOCK

Figure 8-13Reconditioning Block

An important requirement for the lapping process is the perpendicular relationship ofthe valve guiding system, the disc, and the nozzle seat. All valves are designed with aguiding system, an internal component whose function is to direct the disc/disc holderto its designation, the nozzle seat. The guide normally runs in a vertical plane throughthe valve, while the seats (disc and nozzle) run in a horizontal plane through the valve.The nozzle seat is permanently fixed in the horizontal plane. The disc is movable butshould also remain in a horizontal plane. The interface of these two horizontal planes(disc seat and nozzle seat) create the pressure containment seal in a valve.

The degree of tightness of this seal is influenced by the vertical plane of the valve guid-ing system. When this relationship is violated, the seating area is adversely affected andmay result in seat leakage. Failure occurs when either the disc or nozzle seat (or both) isno longer at a 90˚ intercept of the guide plane. This may occur if the valve seats havebeen improperly lapped or machined. Even if the valve seats are flat and have an ac-ceptable finish, valve seat tightness failure may result if they are no longer at a 90º angleto the guiding system. Geometric relationships for the disc and the nozzle as well as thenozzle to body should be obtained from the valve manufacturer if extensive lapping ormachining of the nozzle seat is performed.

8-39



CAUTION: The seating area should be covered with the lap at all times. Failure to do somay result in the loss of the perpendicular relationship between the seat and the valveguiding system.

Lapping time is dependent on the following factors:

• Grit size, coarse compound (320 or less) will remove more material in a shorter timeand will take longer to break down than fine (600 to 900)

• The amount of seat damage that has to be removed

• Pressure that is used during the lapping process

For the majority of lapping, the only pressure necessary will be the weight of the lapalong with the natural force of the arm and hand performing the lapping procedure.Slight pressure may be applied during the use of coarse and medium compounds thatare used to remove damaged seating areas. Care must be used if pressure is beingapplied so as to not loose the perpendicular relationship of the guide with the disc andnozzle seat. Whenever a finish is being created on a seating surface, normal pressure isall that will be necessary. If the proper lap and compound is used in conjunction withthe above principles and concepts, a quality end product will result.

8.4.1.6 Compound Lapping Process

The process of lapping with compound varies according to the type of compound beingused and the desired surface finish. There are several techniques that can be used in thelapping process.

• Fasten the disc in a fixed position (i.e., a vise with brass jaws or similar protection)and lap the disc with the lap in the mechanic’s hand.

• Use a fixed lap with the disc in the mechanic’s hand. The disc-in-hand approachallows the use of the correct size lap or a lapping plate.

• Employ the use of a mechanical lapping machine (Lapmaster or equivalent), ifavailable.

All the above will produce acceptable results. The nozzle will limit the type of tech-nique that can be used due to its size, weight, configuration, and accessibility.

The preferred technique is a correctly sized lap in the mechanic’s hand. When the discor nozzle are manually lapped, hand motion (technique) should remain relatively stablefor each compound. This motion will consist of a back and forth oscillating motion withas little lateral movement as possible. Lateral movement may cause undue scratching ofthe surface being lapped. This is especially true in the latter stages of the lapping pro-cess (fine and polish grades of compound). Check the lapping block frequently on agood reconditioning plate to be sure that it is perfectly flat.

8-40



If the valve seat is to be microfinished as the final lapping operation using a diamondcompound, use new, clean laps and only the compound and vehicle recommended bythe manufacturer.

8.4.1.7 Lapping Angle Seats

Lapping an angle seat requires different techniques and tools than that of a flat seat. Theangle of the seating surface must be determined (e.g., 3, 5, 10, 15 or 45˚) prior to lapping.This may be accomplished in two ways. The first and recommended way is to usevendor engineering information. If vendor information is not readily available, theangles must be measured manually.

A common application of angle seats has a 15˚ seat opposing a flat seat. In most cases,the seats are independently lapped, with the flat seat being done using normal lappingtechniques. The angle on the mating seating surface must have a flat lapped onto it to apredetermined width. The angle seat should be lapped first, then the flat should belapped to control the seat width. Width of the seat must be carefully controlled. The useof a medium grade lapping compound will establish a desired width. After the seatwidth has been attained, the seat is then polished. The width of the seat will slightlydecrease during polishing. Lapping of this variety of angle seats does not require spe-cial laps. The standard flat, cast iron lap will produce a satisfactory seating surface inany of the above angle configurations.

Some valve applications use angle seating with a 45˚ angle on the disc and a 45˚ angleon the nozzle. This type of seating arrangement requires a different lapping technique.A lap with an identical 45˚ angle is used on the nozzle seat. The lap will have either atop or bottom guiding system. Valve design will dictate which type of guiding systemthe lap will employ.

Cleaning up the nozzle seat can be accomplished with the use of abrasive paper affixedto the 45˚ angle of the lap. The objective here is to prepare the nozzle seat for the use oflapping compound. There are three options that can be used to prepare the disc seat.The first option for minor cleanup of the disc seat is accomplished by placing the disc ina lathe and cleaning the seat with crocus paper. The second option is machining thedisc, and the third, replacing the disc insert.

When the disc and nozzle have been properly prepared, the seats are then lapped to-gether. This is one of the few instances where it is necessary to grind (using lappingcompound) the disc and nozzle seat together. This type of lapping is accomplished withthe use of a medium grade compound. Compound is applied to the disc seating surfaceand the disc and nozzle are ground together in conjunction with the guiding system ofthe valve.

In the case of a bottom-guided (bore) valve, lapping may be accomplished by physicallyturning the disc in the nozzle bore. DO NOT TURN THE DISC IN ONE CONTINU-OUS CIRCULAR MOTION. Divide one revolution into segments with four being thestarting point. The number of segments may increase with an increase in valve size.

8-41



Upon completing one revolution, the disc will be lifted from the nozzle seat (approxi-mately 1/4-inch) and rotated 90˚. Repeat this process several times. The mechanicshould be able to feel the lapping process taking place and the breaking down of thecompound. Conversely, if the disc is galling or dragging (an indication the lappingprocess is incomplete) the mechanic should be able to feel the irregularities. The idealsensation will be that of a smooth uniform grinding action. Lapping in this manneravoids the possibility of the disc riding high to one side or galling of the seating area.

After repeating the above process, inspect the seating area. Inspection is performed aftercleaning the seating area with an approved cleaning solution. The final objective is asolid uniform seat on both the disc and nozzle. Lapping seats together in this fashioncan only be done for a short period of time. Prolonged lapping will eventually lead towearing a groove into the seat. If lapping of the seats does not provide the desiredresults in this time frame, there is usually a problem that must be corrected. The follow-ing are some of the common problems found in this type of seating arrangement:

• A uniform seat is one that has dark graying intermingled with spots of light grayingor no graying at all. This indicates the seats are concentrically true, but the seatingsurface finish is not adequate (low spots). Lapping with abrasive paper again orremachining will correct this problem.

• A seat that has dark graying all the way around it but is not uniform. The seat willbe wide on one side while directly opposite it will be narrow. This usually indicatesan alignment problem that could be created in several ways. The vast majority of thetime it is caused by improper machining (total indicated runout was exceeded caus-ing misalignment in conjunction with the guide). A second possibility, especially intop guided valves, is the misalignment of the guide in conjunction with the nozzle.

• Graying of the seating area only at the top or bottom usually indicates that a metalburr is present and the seat is not making full contact with the mating seat. Removalof the burr can normally be accomplished with a fine file or similar device.

Once the final seat finish has been obtained, the seating area should be cleaned of anyexcess compound with an approved cleaner.

8.4.1.8 Final Inspection of Lapped Seating Surfaces

A final inspection of the lapped seating surfaces is performed to determine if the lappedsurface is flat and has an acceptable surface finish. Either of the following approachescan be taken to determine if the seats are flat.

Visual Inspection

The first method is visual inspection. Adequate lighting is essential for this type ofinspection. There are two criteria that the seat inspection must pass. The first criteria isthe absence of any physical damage in the seating area. If the seat passes the first crite-ria it is then inspected for any signs indicating unacceptable finish or flatness. This partof the inspection process requires the rotation of the seat (if practical) so that the light

8-42



can reflect off the surface at different angles. Rotating the seat in this manner reducesthe chance of missing an imperfection. Specific imperfections that must be corrected are:

• Areas that are highly polished intermixed with areas with a dull lustre

• Fine scratches created during the lapping process (especially if they are groupedtogether)

• A seat is not lapped completely to the outside or inside edge yielding a uniform ringalong the edge of the seat

• A solid ring (dull lustre) running in the middle of or across the seat width

Optical Flat

Inspection with an optical flat and monochromatic light is the second method. How-ever, as was discussed in Section 8.4.1.5, this method is difficult to use and may not beapplicable in many cases.

8.5 PRV Control Rings and Their Settings

Section 4 reviewed PRV design and theory. It also discussed the reason for, the impor-tance of, and the effect of control rings on valve performance. With this background, itis easy to understand the importance of the positioning (setting) of these rings after themaintenance activity is complete and the valve is reassembled. First, a review of somebasics in ring settings:

• Each manufacturer has a unique method of setting rings.

• Do not attempt to use one manufacturer’s method of setting rings on anothermanufacturer’s design.

• Ring setting for each manufactured valve has been established by: a) a factory teston that specific valve, or b) based on the manufacturer’s test data for that particularvalve style. This is based on ASME Code and/or valve design or valve specificationat time of valve purchase.

• Ring settings effect valve performance (i.e., opening characteristics and closing orblowdown) and should not be changed unless the valve is retested or by specificinstructions from the valve manufacturer.

• If a set pressure change is made on a valve, consult the valve manufacturer for theeffect of that change on the ring setting (i.e., valve may have to be operationallyretested).

• The ring pins (or set screws) that are installed threaded into the valve body andengaged in a notch or groove in the control ring are fit for each valve. Do not inter-change them with ring pins from other valves.

In summary, it is important that during the maintenance activity: 1) the location of thecontrol ring(s) are confirmed at the time of valve disassembly, and 2) the setting of thecontrol rings during or after (depending on manufacturer’s design) valve assemblyshould be done strictly in accordance with the manufacturer’s instruction manual.

8-43



Subsections 8.6 through 8.11 review the disassembly and assembly of three differenttypes of PRVs: pressurizer, main steam, and auxiliary-relief application. It is importantto note how each design has a different method of setting the guide ring.

8.6 Disassembling and Assembling Typical PRVs

To this point in Section 8, a broad overview of the maintenance activities on PRVs hasbeen provided. However, there has not been a review of any disassembly or assemblymethods. To provide a better understanding of these operations and to illustrate theimportance of using the manufacturer’s instruction manual, three different valve de-signs of a single manufacturer (Crosby) have been selected to demonstrate how similarthis operation is in some areas, but dissimilar in others (e.g., valve ring settings). Theoperation will be performed using two methods of disassembly: 1) retaining the springcompression (sometimes called jack and lap), and 2) without retaining the spring com-pression (or total disassembly) on a pressurizer, a MSSV, and an auxiliary valve.

8.6.1 Disassembling and Assembling Pressurizer Safety Valve

The first valve used to perform a disassembly and assembly operation is a Crosbypressurizer safety valve. The valve size is a 6-inch inlet, “M” orifice with a 6-inch outlet(Crosby Style HB-86-BP). The valve set pressure is approximately 2500 psig, its heightapproximately 48 inches, and its total weight 1100 lbs. A valve outline drawing withpiece names and numbers is shown in Figure 8-14.

8-44



25?

2436

2328

2726

A A

37 20 19 49 14B

48

38 39 33 34 1114A

6 5 10 9 7 3

31

43

32 2144

17 16 22 23

39B

39A

30

29 28 14

18 20

40 41 15 47 49 8 12 35 13 35 4 1 2

42 16

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Bon

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ew43

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8-45



8.6.2 General Information

When possible, remove the valve from the system before dismantling. In any case, thereshould be no system pressure when a valve is either dismantled in place or removed forshop repair.

Several flat metal gaskets are employed for sealing joints. Care must be exercised whendismantling not to damage or lose these gaskets as they can be reused. Gasket locationscan be determined by referring to Figure 8-14.

Nozzle and guide ring set screws are custom fitted to each valve and are not inter-changeable.

Spring washers are fitted to each end of the spring. The spring and its washers are to bekept intact as a unit.

Certain pieces, as covered in the ASME Section III NV-1 form, are serialized. In disas-sembly and assembly, confirm and reinstall only pieces that match the documentation.

8.7 Pressurizer Valve Disassembly

The proper procedure for dismantling a safety valve is described below (see Figure 8-14and 8-15).

8.7.1 Remove the Cap

Remove the lifting lever (28), the cap top (43), and the spindle nut cotter (17). Next,unscrew spindle nut (16) from the spindle and remove cap nuts (39A) and cap (21).

8.7.2 Record Ring Settings

Remove the adjusting and nozzle ring set screws (4 and 13). Check the setting of thenozzle ring (3) by turning it to the right while counting the number of notches turneduntil it makes contact with the disc ring (7). Record the number of notches. Check thesetting of the adjusting ring (12) by turning it to the right while counting the number ofnotches turned until it makes contact with the disc ring (7). Record the number of notches.

8.7.3 Disassembly Retaining Spring Compression

If the valve is to be reconditioned without retesting, the original set pressure can beretained by use of a jacking device shown in Figure 8-15.

Tabulation of Crosby piece numbers for the hydraulic jacking device are shown inFigure 8-15(b).

Install bonnet spacer (5) on the bonnet. Position jacking device assembly by lifting theassembly over the spindle (14) and lowering it down onto the bonnet spacer (5).

8-46



CAUTION: The piston (2) should be seated within housing (1) before continuing. Thisposition is reached when the first notch on the piston (2) is level with or below the top of thehousing (1) as indicated in Figure 8-15(a).

Lubricate the spindle threads with Never-Seez, Molykote-G, or an equivalent. Threadthe spindle adapter (6) onto the spindle until the spindle adapter comes into contactwith the jacking device assembly. Next, attach the hand-operated hydraulic pump (7)and hose (8).

To raise the valve spindle, pressure is applied to the jacking device assembly with thehand operating hydraulic pump. This actuates the piston (2) which raises the lowerspring washer compressing the spring.

CAUTION: This device has a limited piston stroke that should not be exceeded. Thesecond notch on the piston (2) will be above the top of the housing (1) and hydraulic fluid willflow from the bleed hole located in the housing. If hydraulic fluid is flowing from the bleedhole, but piston stroke has not been exceeded, the O-rings (3 and 3A) and the back-up rings(4 and 4A) should be inspected for wear or damage and replaced, if necessary. Removal ofthe jacking device for repair may be accomplished by the releasing procedure, the reverseof the procedure used above for its installation.

After the valve has been jacked approximately 1/8-inch (3mm) and the spring load hasbeen taken up by means of the jacking device, remove the adjusting ring set screw (13),nozzle ring set screw (4), loosen and remove bonnet stud nuts (39), and then lift thecomplete bonnet (18) assembly from the valve body (1).

The valve may now be further disassembled for maintenance as follows.

CAUTION: In removing the disc holder and bellows assembly from the spindle, careshould be exercised not to damage the bellows. The spindle should also be protectedagainst any damage (bending) while handling.

Remove the adjusting ring (12) from the eductor (11). Remove the disc insert pin (10),disc insert (9), and disc ring (7). Slide the eductor (11) over the disc holder (5). The discholder (5) and bellows assembly (8) may now be unscrewed from the spindle (14), andthe bonnet adapter (15) can be lifted over the spindle (14).

8-47



HO

US

ING

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N

"O"

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1 2 3 3A 4 4A 5 6 7 8 14 20 26 27

7 8 14 6 2

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raul

ic J

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(B)

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re 8

-15

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Val

ve

8-48



8.7.4 Disassembly without Retaining Spring Compression

If it is desired to completely disassemble the valve and not retain the spring compres-sion, the following procedure should be used.

1. Measure the length of the spindle (14) above the adjusting bolt (29), and record thedimension so the same distance can be reestablished when reassembling the valve.

2. Release the spring tension by loosening the adjusting bolt locknut (30) and then theadjusting bolt (29).

WARNING: Never loosen bonnet nuts before releasing spring tension with theadjusting bolt.

3. Loosen the bonnet nuts (39) holding the bonnet (18) to the body (1) of the valve. Liftthe bonnet (18) up to clear the spindle (14) and spring (19). Remove the spring (19)and washers (20).

4. The spindle (14), bellows (8) and disc holder assembly, and eductor (11) should belifted out of the valve as a complete unit. Place this assembly on a clean, soft mate-rial to insure no damage occurs to the disc insert (9) seating surface.

5. Remove the spindle (14) from the disc holder assembly and the adjusting ring (12)from the eductor (11). Next, remove the disc insert pin (10).

CAUTION: The disc insert pin (10) is flared at one end and should be removed by drivinga drift pin into the hole from the non-flared end while resting the opposite end on a softwooden block to insure that no damage occurs to the disc ring.

6. After the removal of the disc insert pin (10), the disc insert (9) can be removed fromthe disc holder (5), and the disc ring (7) can be unscrewed from the disc holder (5).The disc holder and bellows assembly can now be removed from the eductor (11).

7. Remove the nozzle ring (3) from the nozzle (2).

8. When the valve is completely disassembled, examine all parts for signs of wear,damage or corrosion to determine whether any replacement parts are required.Particular care should be taken to examine for wear or scoring the inside of theeductor (11), the outside of the disc holder (5), the inside of the bonnet adapter (15),and the piston (40).

8-49



8.8 Pressurizer Valve Assembly

8.8.1 General

Prior to any assembly operation, the valve seats should be relapped and other parts recon-ditioned, cleaned, lubricated, and then assembled. This would be accomplished as follows:

1. Lap valve seats per instructions.

2. Parts should be thoroughly cleaned. A fine emery cloth or crocus cloth may be usedto polish guiding and bearing surfaces and surfaces in intimate rubbing contact.Care must be used to ensure that the critical dimensions are not affected.

3. Examine all gasket sealing surfaces and gaskets. If they are damaged, the surfacesshould be polished and the gaskets replaced.

4. Finally, clean parts with acetone or any other acceptable cleaner prior to assembly.

The following areas should be lubricated before and during assembly with a suitablesealant or lubricant as indicated against each item:

• All gaskets and gasket surfaces - sealant

• Nozzle-to-body threads - lubricant

• Adjusting bolt threads - lubricant

• Spindle point threads - lubricant

• Spring-washer bevels - lubricant

• Cap top threads - lubricant

• Cap plug threads - lubricant

• Set screw threads - lubricant

• Dog shaft bearing threads at ID - lubricant

• All studs and nuts - Never-Seez or equivalent

• Eductor and guide ring threads - lubricant

• Disc ring and disc holder threads - lubricant

• Nozzle ring to nozzle threads - lubricant

• Piston OD and bonnet adapter ID - powdered graphite or Neolube

8.8.2 Assembly of Valve with Spring Compression Retained

The bonnet and jacking device assembly with spring, spring washers, and spindleshould be placed on a work bench with the spindle horizontal.

Place the gasket on the bonnet adapter (15) and place the adapter over the spindle.

8-50



Place the bellows assembly (5, 6, and 8) onto the spindle (14) and turn it on the spindleuntil it drops off the spindle thread and spins freely.

NOTE: If a new bellows is installed, the bellows flange surfaces should be lapped withmedium compound against the bonnet adapter and eductor surfaces until a satin dull finishis obtained on the bellows flange across the sealing face. This operation is performed topreclude the possibility of leakage across the gasket surface.

The eductor (11) should be installed over the bellows assembly (5, 6, and 8).

Assemble the disc ring (7) with lubricated threads onto the disc holder (5). The throughholes in the disc ring (7) and disc holder (5) must be in alignment. Assemble the discinsert (9) using the disc insert pin (10) (Note: see caution in section on disassembly). If anew pin is installed, one end should be flared prior to assembly. The adjusting ring (12)can then be screwed onto the eductor (11).

Install the nozzle ring (3) on the nozzle (2) locating it approximately 1/32-inch abovethe seat level of the nozzle.

CAUTION: Perform a final inspection and clean the nozzle and disc insert seating surface.

The entire jacked assembly, complete with eductor, bellows, disc insert and all the otherparts described above, may now be lowered carefully into the valve body and thebonnet studs (39) tightened as follows.

1. Valve studs and nuts should be cleaned and visually inspected to ensure freedomfrom any objectionable foreign matter, rust, burrs, or physical damage.

2. With the bonnet in place, lubricate the bonnet stud threads, the nut threads and nutface with Never-Seez compound.

3. Install nuts on the studs finger-tight.

4. Tighten the nuts in the sequence shown in Figure 8-21 to approximately one-half therequired torque value. Repeat the same sequence of tightening to .75 times therequired torque value. Then perform the final tightening operation starting with thenumber 1 nut and tighten each nut in order in a clockwise or counter-clockwisedirection to the final required torque value.

5. When tightening is complete, wipe off excess lubricant.

6. Lower the nozzle ring (3) by turning it to the left (clockwise when facing the setscrew hole) until it is in the lowest free position, and then lower the adjusting ringuntil the lower edge is below the level of the nozzle seat.

8-51



7. The jacking device may now be removed by reversing the instructions described inthe section on disassembly retaining spring compression.

8. Adjust the nozzle ring (3) by turning it to the right until it makes contact with thedisc ring (7). Then turn the nozzle ring to the left the same number of notches re-corded prior to disassembly. Adjust the adjusting ring (12) (that should also be resetto its original location recorded prior to disassembly) by turning it to the right untilcontact is made with the disc ring. Then turn to the left and count the notches untilthe same number of recorded notches is reached.

9. Replace the adjusting ring, nozzle ring set screws (4 and 13), and gasket (35), beingsure the point engages the notch.

10. The cap (21), spindle nut (16), and lifting gear assembly are assembled by reversingthe procedure used in the disassembly operation. Make sure the lifting gear dog (22)has the curved side up so the curve will contact the spindle nut (16) when the leveris lifted. The spindle nut should be adjusted, and the lever (28) put on so the dog (22)is not bearing on the spindle nut (16) until the lever is lifted to about the positionshown in Figure 8-14. Replace the spindle nut cotter pin (17).

8.8.3 Assembling a Pressurizer PRV

Place the bellows assembly (8) on a clean flat surface with the disc holder (5) up. If anew bellows is installed, perform the same procedure on bellows as described if thevalve was disassembled retaining spring compression.

1. Place the eductor (11) over the bellows assembly (8).

2. Assemble the disc ring (7) with the threads lubricated on the disc holder (5). Thethrough holes in the disc holder (5) and the disc ring (7) must be in alignment. As-semble the disc insert (9) using the disc insert pin (10). Note: See caution in sectionon valve disassembly. If a new pin is installed, one end should be flared prior toassembly.

3. The adjusting ring (12) may then be screwed onto the eductor (11).

4. The assembly may now be turned over so the disc insert is down and the flange onthe bellows assembly is up.

CAUTION: When placing this unit on a bench, make certain that the disc insert seat isprotected from damage.

5. Place the bonnet adapter (15) on top of the bellows flange.

6. Lubricate and assemble the spindle (14) into the disc holder (5) until the threadsdrop into the undercut in the disc holder and the spindle rotates freely.

8-52



7. Install the nozzle ring (3) on the nozzle (2) locating it approximately 1/32 inch abovethe seating surface of the nozzle (2). Final inspect and clean the nozzle and discinsert seating surface.

8. Lift the bellows, eductor, adjusting ring and bonnet adapter assembly straight upwith the spindle (14) and lower it straight down into the body (1) until the disc ring(7) rests on the nozzle ring (3).

9. Install the lower spring washer (20), the spring (19), and the upper spring washer(20).

10. Install the bonnet (18) and assemble and tighten the nut (30) as described in thesection on assembly with spring compression retained.

11. Lower the nozzle ring (3) by turning to the left (clockwise when facing set screwhole) until it is in the lowest free position, then lower the adjusting ring (12) until thelower edge is below the level of the nozzle seat.

NOTE: If difficulty is encountered in lowering the nozzle ring, lift up on the spindle (14)while lowering the nozzle ring.

12. Replace the adjusting bolt (29) turning it down until the length of the spindle (14)above the adjusting bolt (29) measurement is the same as before disassembly.Tighten the adjusting bolt nut (30) to lock the adjusting bolt (29).

NOTE: At this point, the valve can be bench tested if desired in accordance with the utilitytest procedure.

13. Adjust the nozzle and adjusting ring by following the procedure as described inassembly of the valve with spring compression retained.

14. Replace the cap (21), spindle nut (16), and lifting gear, etc., by following the proce-dure described in the paragraph on assembly with spring compression retained.

8.9 Disassembly and Assembly of MSSVs

The second valve used to perform a disassembly and assembly operation is a typicalCrosby MSSV. The valve size is a 6-inch inlet, “R” orifice, 10-inch outlet Crosby StyleHA-75-FN (full nozzle) with a set pressure of approximately 1200 psig. The valve isapproximately 64 inches high with an approximate weight of 1550 lbs. The outlinedrawing of the valve and piece name and numbers are shown in Figure 8-16.

8-53



54"Approx.HeightFromoutlet

ConcentricSeparations

9 3/4

+1/4-1/8

12 3/4DIA

±1/32

10"DIA

±1/8

1" MAX

1/4±1/64

5 1/8 MIN

SeeNote 4

5 5/8Approx.

6"DIA

±1/8

8 1/2 DIA±1/64

34" MINWorking Space

ConcentricSeparations

1/6Approx.

OUTLET

42

1

2

6

3

4

3411

8A353637

49

50

388B

222114

25

15

27

29

33

23

32

31

34

28

29

30

19

24

18

17

16

13

12B

20

12C

12A

5A5B

1012D7

1/16±1/64

9 1/4+1/4-1/8

24" MAX

19"MAX

INLET6" 1500# ANSI STD. RF.12 Studs 1 3/8-8 UN-2AEqually Spaced on a 12-1/2 DIA E.C.And Straddling CL's

OUTLET10" 300# ANSI STD. R.F.16 Holes 1"-8 UNC-3BEqually Spaced on a15-1/4 DIA B.C.And Straddling CL's1-1/8 Min. Thd. Depth

Lever Can BeRotated 180˚ from

Position Shown

Piece Part Name No.

1 Body2 Nozzle3 Nozzle Ring4 Nozzle Set Screw5A Disc Holder5B Disc Bushing6 Disc Insert7 Disc Insert Pin8A Guide8B Guide Bearing10 Guide Ring11 Guide Ring Set Screw12A Spindle Point12B Spindle Rod12C Spindle Rod Pin12D Spindle Ball13 Spring14 Spring Washer (bottom)15 Spring Washer (top)16 Bearing Pin17 Bearing18 Bearing Adapter19 Adjusting Bolt Nut20 Bonnet21 Bonnet Stud22 Bonnet Stud Nut23 Cap24 Cap Set Screw25 Lever26 Lever Pin27 Lever Pin Cotter28 Fork Lever29 Fork Lever Pin30 Fork Lever Pin Cotter31 Spindle Nut32 Spindle Nut Cotter33 Adjusting Bolt34 Seal & Wire35 Data Plate36 Nameplate37 Identification Plate38 Drive Screw

1" Approx.

14" Approx.

C.G. ValveOnly

OUTLET

Figure 8-16Typical Crosby MSSV

8-54




When possible, remove the valve from the system before dismantling. In any case, thereshould be no system pressure when a valve is either dismantled in place or removed forshop repair.

8.9.2 MSSV Disassembly

The safety valve may be disassembled in two ways, either retaining spring compression(and, thereby, retaining the original set pressure) or not retaining spring compression.For either method, disassembly proceeds as described below.

8.9.2.1 Remove the Lifting Gear

To remove the cap (23), remove the forked lever pin (29) and forked lever (28) and thelever pin (26) and lever (25). Loosen the cap screws (24) and remove the cap. Removethe spindle nut cotter (32) and unthread the spindle nut (31).

8.9.2.2 Record Ring Settings

Remove the guide ring set screw (11) and nozzle ring set screw (4). Check the setting ofthe nozzle ring (3) by turning it to the right (counter clockwise) while counting the num-ber of notches turned until it makes contact with the disc holder as shown in Figure 8-17.Record the number of notches. This location is given as a minus (-) notches from thiscontact position. The guide ring (10) should be turned to the right (counter clockwise) orleft (clockwise) whichever is necessary to return it to its level position. The guide ring is inlevel position when the bottom face of the guide ring is level with the bottom face of thedisc holder (5). This can be determined visually or with a metal rod as illustrated inFigure 8-17. The guide ring position is recorded as minus (-) (down) or plus (+) (up)notches from this level position.

NOTE: Confirm that as-found ring settings are identical to those stamped on the bonnet(see Figure 8-18a) and in plant documentation records.

8-55



Nozzle Ring

Disc Holder

Disc

N Notchesdown fromtouching

Where,N = Factory settingstamped on the Bonnet

Steel Rod ToCheck GuideRing Position

Disc Holder

Level Position*

Cotter Pin

GuideRing

Nozzle Ring Setting

Guide Ring Level with Disc Holder*Factory setting of Guide Ring Position (+ or -) Notches from Level stamped on Bonnet.

+-

Figure 8-17Illustrations of Nozzle Ring Setting and Guide Ring Level

8-56



INSTALL HYDRAULIC JACKINGDEVICE HERE

NOZZLE RING AND ADJUSTING RING

SETTINGS STAMPEDHERE

THREE STEELBLOCKS

VALVEBODY

(a)

HOUSING

PISTON

"O" RING

"O" RING

BACK-UP RING

BACK-UP RING

BONNET SPACER

SPINDLE ADAPTER

HYDRAULIC PUMP

1/4" HOSE

VALVE SPINDLE

BONNET

ADJUSTING BOLT

ADJUSTED BOLT NUT

BLEEDHOLE

1/4 18-NPT

1

2

3

3A

4

4A

5

6

7

8

14

20

26

27

7

8

14

6

2

3A 4A

3 4

12627520

PISTON STROKEINDICATOR

HYDRAULIC JACKING DEVICE

*RECOMMENDED SPARE PART

*

*

*

*

*

(b)

Figure 8-18Illustration of MSSV (Jacked) and Location of Ring Setting Marking

8.9.2.3 Disassembling Retaining Spring Compression Usinga Hydraulic Jacking Device

If the valve is to be reconditioned without retesting, the original set pressure can beretained by use of a hydraulic jacking device as shown in Figure 8-18.

After removing the lifting gear and recording of the ring settings per Figure 8-16, disas-sembly retaining the spring compression is performed as follows:

1. Measure from the bottom face of the bottom spring washer to the bonnet flange topface and record the dimension. Cut three pieces of bar stock, minimum 50mm indiameter (approximately 2 inches) 3mm (1/8-inch) longer than the recorded dimen-sion. These spacer blocks will be placed between the bottom spring washer and thebonnet flange after the spring has been compressed.

2. Position the jacking device assembly (see Figure 8-18b) by lifting it over the spindle(14) (Piece 12 on Figure 8-16) and lowering down onto bonnet (20).

8-57



CAUTION: The piston (2) should be seated within the housing (1) before continuing. Thisseated position is reached when the first notch on the piston (2) is level with or below the topof the housing (1) as indicated in Figure 8-18b.

3. Lubricate the spindle threads with Never-Seez or an equivalent. Thread the spindleadapter (6) until it comes into contact with the jacking device assembly, and attachthe hand-operated hydraulic pump (7) and hose (8).

4. To raise the valve spindle, apply pressure to the jacking device assembly with thehand-operated hydraulic pump. This activates the piston (2) which raises the lowerspring washer that compresses the spring.

CAUTION: This device has a limited piston stroke that should not be exceeded. If thepiston stroke is exceeded, the second notch on the piston (2) will be above the top of thehousing (1) and hydraulic fluid will flow from the bleed hole located in the housing. If hydrau-lic fluid is flowing from the bleed hole but piston stroke has not been exceeded, the O-rings(3 and 3A) and the back-up rings (4 and 4A) should be inspected for wear or damage andreplaced if necessary.

5. After the spring load has been taken up and the valve has been jacked approxi-mately 1/8-inch, place three spacer blocks under the lower spring washer.

6. The jacking device can now be removed by releasing pressure in the pump andreversing the above procedure.

7. Referring to Figure 8-16, remove the guide ring set screw (11) and the nozzle ring setscrew (4).

CAUTION: Never loosen the bonnet stud nuts before taking up the spring compressionload with the spacer blocks.

8. Loosen and remove the bonnet stud nuts (22). There are two ways to remove thepieces from the valve body. They are as follows:

• Using a suitable lifting device, lift the bonnet and spring assembly vertically to clearthe spindle.

CAUTION: The spring washers are fitted to each end of the spring. The spring and wash-ers must be kept intact as a unit.

8-58



• The spindle assembly (12), disc holder (5A), guide (8A), guide ring (10), and discinsert (6) can be removed from the valve body as a complete unit by carefully liftingthe spindle rod (an eye nut can be attached to the spindle rod end and used in con-junction with a hoist).

CAUTION: Do not permit any rocking motion of the spindle or any other parts while liftingthem out of the body. Any rocking motion could damage the valve seats.

Lower the complete assembly onto a clean flat surface. Lift the spindle rod (12B) slightlyto engage the disc holder threads and unscrew the spindle (12) from the disc holder(5A). Lift the spindle up and out of the guide assembly. Remove the guide ring (10)from the guide (8A). The disc insert (6) can be removed from the disc holder by remov-ing the disc insert pin (7). Remove the nozzle ring (3) from the nozzle (2).

When the valve is completely dismantled, examine all parts for signs of wear, damage,or corrosion to determine if any replacement parts are required. Particular care shouldbe used to examine the inside of the guide, the outside of the disc holder, and thespindle surface that is guided by the guide for wear or scoring.

8.9.2.4 Disassembly (without Retaining Spring Compression)

After the lifting gear is removed and the ring settings are recorded as covered in an earlierparagraph, disassemble the valve without retaining the spring compression as follows:

1. Remove the spindle nut cotter (32), spindle nut (31), and cap (23). Measure thedistance between the top of the bonnet and the top of the adjusting bolt and recordthis measurement. This measurement will be necessary when the valve is reas-sembled.

2. Release spring tension by loosening the adjusting bolt locknut (19) and then theadjusting bolt (33).

CAUTION: Never loosen the bonnet stud nuts before releasing the spring tension with theadjusting bolt.

3. Remove the guide ring set screw (11) and the nozzle ring set screw (4).

CAUTION: Nozzle and guide ring set screws are custom fitted to each valve and are notto be interchanged.

8-59



4. Lift the bonnet and spring up to clear the spindle using caution to prevent the springfrom falling out of the bonnet. Remove the spring and washers from the bonnet.Remove the adjusting bolt (33) and the adjusting bolt nut (19) from the bonnet andthoroughly clean the threads.

CAUTION: The spring washers are fitted to each end of the spring. The spring and wash-ers must be kept intact as a unit.

Disassembly from this point proceeds as in the paragraphs covered in Section 8.9.2.3,Disassembly Retaining Spring Compression Using Hydraulic Jacking Device.

8.10 MSSV Assembly

8.10.1 General

Prior to any assembly operation, the valve seats should be relapped and other partsreconditioned, cleaned, lubricated, and then assembled. This is accomplished as fol-lows:

1. Lap the valve seat per instructions.

2. Clean all parts thoroughly. A fine emery cloth or crocus cloth may be used to polishguiding and bearing surfaces and surfaces in intimate rubbing contact. Care must betaken to ensure that the critical dimensions are not affected.

3. Check all bearing surfaces before assembly to ensure that they are free of nicks orgouges on the surface.

4. Finally, clean parts with acetone or any other acceptable cleaner prior to assembly.

The following areas should be lubricated before and/or during assembly with suitablelubricant.

• Nozzle-to-body threads

• Adjusting bolt and bonnet threads

• Spindle point threads

• Spindle ball

• Spindle rod threads

• Spring washer bevels

• Set screw threads

• All studs and nuts

8-60



8.10.2 Assembly of Valve (Spring Compression Not Retained)

Refer to Figure 8-16.

1. Install the disc insert (6) into the disc holder (5). Install the disc insert pin (7) andbend the pin ends making certain that the pin cannot move in a manner that willallow either end to extend beyond the OD of the disc holder.

CAUTION: Care should be used in the assembly operation to insure against damage ofthe disc insert seat.

2. Screw the guide ring (10) onto the guide (8). Install the disc holder (5) in the guide.Lubricate the spindle point (12A) threads and spindle ball (12D). Insert the spindlepoint through the guide bearing and into the disc holder. Screw the spindle clock-wise until it drops off the bottom thread of the disc holder, and the spindle ball is incontact with the disc bushing (5B). The spindle should spin freely.

3. Screw the nozzle ring (3) onto the nozzle (2). Leave the nozzle ring to 3mm (approxi-mately 1/8 inch) above the nozzle seat.

4. Lift the assembly of spindle (12), disc holder (50), guide (8A), guide ring (10) anddisc insert (6) into position over the valve body (1). Carefully lower the assemblyinto the body until the guide flange is seated flat on the top of the body and the faceof the disc holder contacts the nozzle ring (3). Rotate the spindle to be sure thespindle ball (12D) is in contact with the disc bushing (5B).

5. Install the bearing (17) and bearing adapter (18) on the top spring washer (15). Lu-bricate the bearing adapter bevel and the bottom spring washer (14) bevel. Place thebottom spring washer in position in the bonnet. Position the spring (13) on thebottom spring washer, and place the top washer assembly on the spring. Strap thespring assembly to the bonnet to hold it in place.

6. Lubricate the adjusting bolt (33) threads. Screw the adjusting bolt locknut (19) ontothe adjusting bolt all the way to the end of the adjusting bolt thread. Lubricate thebonnet (20) threads. Screw the adjusting bolt into the bonnet. Leave a 6 to 13mm (1/4- to 1/2-inch) gap between the bearing adapter and the adjusting bolt.

7. Lift the assembly of bonnet (20), spring (13) and spring washers (14 and 15) over thespindle (11). Carefully lower the assembly, guiding the spindle through the springwashers and adjusting the bolt (33). Position the bonnet over the body-to-bonnetstuds (21). Lower the bonnet onto the guide (8A) taking care not to damage the studthreads. Screw the adjusting bolt upwards during this process, if necessary, to main-tain a minimum 3mm (1/8-inch) gap between the adjusting bolt and the bearingadapter (18). Make sure the bonnet is fully seated on the guide.

8. Install the bonnet nuts (22) on the bonnet studs (21) and uniformly tighten in accor-dance with the recommended bolting procedure and torque values.

8-61



CAUTION: After the bonnet nuts have been tightened, lift up the spindle as before (ap-proximately 1 inch). Place a screwdriver in the nozzle ring set screw (4) hole and turn thenozzle ring to the left (clockwise) until the top edge of the nozzle ring is below the nozzleseating surface. Lower the spindle assembly slowly until it bottoms out. The nozzle and discinsert seating surfaces are now in intimate contact. Be sure the spindle ball is in contact withthe disc bushing and not caught on the disc holder thread. This is done by rotating thespindle assembly clockwise.

9. Before tightening the adjusting bolt, rotate the spindle to be sure that it is free tomove with the spring. This is done to ensure that there is no binding within thevalve that could cause faulty operation. It also ensures that the spindle is not caughton the disc holder threads but is seated on the disc holder bushing.

10. Tighten the adjusting bolt until the distance between the top of the adjusting boltand the top of the bonnet is the same as that recorded at the time of disassembly.Unless considerable lapping or machining has been done, the set pressure should bealmost the same as before reconditioning.

11. Having recorded the ring positions at disassembly, follow the procedure for locatingrings, discussed in Section 8.9.2.2 and shown in Figures 8-17 and 8-18, to return therings to the recorded location. Lock the set screws in place making sure that the setscrews are engaged in a notch and that the rings are free (have slight side to sidemovement).

12. Replace the lever and lever pin. Install the forked lever and spindle nut leavingapproximately 1.5mm (approximately 1/16-inch) clearance between the spindle nutand forked lever. Make sure the clearance is adequate and that the spindle nut cotterpin is installed properly. Replace the cap top.

13. Protect the valve inlet and outlet and place in an area ready for the next operation.

8.10.3 Assembly of Valve (Spring Compression Retained)1. Install the nozzle ring (93) onto the nozzle (2), leaving the nozzle ring about 1.5 to

3mm (1/16 to 1/8 inch) above the nozzle seating surface.

2. Install the bonnet assembly (including internal parts) into body bowl.

3. Install the bonnet stud nuts (22) on the bonnet studs (21) and uniformly tighten inaccordance with the proper bolting procedure. Remove the spacer blocks fromunder the lower spring washer transferring the spring load to the valve seat. This isaccomplished by repeating the procedure to remove the spacer blocks and thenremoving the jacking device in the assembly procedure.

8-62



CAUTION: After the bonnet nuts have been tightened, lift up the spindle as before (ap-proximately 1 inch). Place a screwdriver in the nozzle ring set screw (4) hole and turn thenozzle ring to the left (clockwise) until the top edge of the nozzle ring is below the nozzleseating surface. Lower the spindle assembly slowly until it bottoms out. The nozzle and discinsert seating surface are now in intimate contact. Be sure the spindle ball is in contact withthe disc bushing and not caught on the disc holder thread. This is done by rotating thespindle assembly clockwise.

4. Having recorded the ring positions at disassembly, follow the procedure for locatingrings discussed in Section 8.9.2.2 and shown in Figure 8-17 to return the rings to therecorded location. Lock the set screws in place making sure that the set screws areengaged in a notch and that the rings are free (have slight side-to-side movement).

5. Reinstall the cap, lever, and forked lever assembly. Install the spindle nut leavingapproximately 1.5mm (1/16 inch) clearance between the spindle nut and forkedlever.

8.11 Auxiliary PRVs

As discussed in Section 4, there are a variety of PRV manufacturers, valve sizes, andvalve types used on auxiliary systems. This section reviews the disassembly and assem-bly of only one valve to illustrate that the maintenance of this valve is similar to theprevious valves discussed, but also dissimilar, requiring that the person performing thisactivity follows the manufacturer’s instructions.

Valves on auxiliary systems are usually flanged and easy to remove from the system formaintenance and testing.

In this section, disassembly and assembly of a Crosby 3/4-inch inlet, “D” orifice, 1-inchoutlet Style JB-TD valve used on gas service is discussed. The valve has a set pressure ofapproximately 70 psig and is approximate 16.25 inches high with a weight of 32 lbs. Theoutline drawing of the valve and its piece names and numbers are shown in Figure 8-19.

8-63



Piece Part Name No.

1 Body2 Nozzle3 Nozzle Ring4 Set Screw5A Bellows5B Disc Holder5D Bellows Adapter Plug6 Disc Insert7 Disc Insert & Ring Pin8 Disc Ring13 Guide14A Spindle14B Spindle Ball15 Spring16 Spring Washer17 Bonnet18 Bonnet Stud19 Bonnet Stud Nut20 Adjusting Bolt21 Adjusting Bolt Nut23 Set Screw Gasket24 Bellows Adapter Gasket26 Guide Gasket27 Cap28 Cap Gasket29 Dog Cam30 Dog Cam Bearing31 Dog Cam Bearing Gasket32 O-Ring33 Lever34 Lever Pin35 Lever Spacer36 Spindle Nut37 Spindle Nut Cotter38 Cap Plug39 Cap Plug Gasket40 Seal & Wire41 Seal Clip42 Test Rod49 Nameplate50 Identification Plate51 Drive Screw52 Inlet Stud

27

3637

14A202141

40

3938

68

52

3130342935323328161517

1618195D135A5B740423312

Figure 8-19Crosby Style JB-TD PRV

8-64




When possible, remove the valve from the system before dismantling. In any case, thereshould be no system pressure when a valve is either disassembled in place or removedfor shop repairs.

Several flat metal gaskets are employed for sealing joints. Care must be exercised dur-ing disassembly not to damage or lose these gaskets as they can be reused. Gasketlocations can be determined by referring to the assembly drawing.

Spring washers are custom fitted to each end of the spring. The spring and its washersshould be kept intact as a unit.

CAUTION: To ensure proper valve operation, care must be taken to accurately measureand record the adjusting ring settings (nozzle ring, guide ring, or guide and ring).

8.11.2 Disassembling Auxiliary PRVs1. The first operation in the disassembly procedure is to determine the position of the

nozzle ring. The level position of the nozzle ring (3) is when the ring is in contactwith the disc ring (8). Therefore, its operating position always has a negative valuebecause its movement is away from the disc ring.

2. Determine the position of the nozzle ring (3) by removing the set screw (4). Use ascrewdriver or similar tool to engage the notches on the nozzle ring through the setscrew hole. While counting the notches, move the nozzle ring counter clockwise asviewed from the top of the valve until the ring stops moving. Record the number ofnotches moved and locate the nozzle ring in the same position when reassemblingthe valve.

3. Remove the cap (27) and the lifting gear assembly by first unscrewing the dog cambearing (30) while holding the lever (33). Unscrew the cap (27).

4. Before removing the spindle nut (36), take a measurement from the bottom face ofthe nut to the top face of the bonnet (17). Record this measurement and use it whenreassembling the valve to obtain the same location of the spindle nut (see Figure 8-20a).

5. Before loosening the adjusting bolt nut (21), take a measurement from the top face ofthe nut to the top face of the adjusting bolt (20). Record this measurement and use itwhen reassembling the valve to obtain the approximate set pressure (see Figure 8-20b).

8-65



Rec

ord

Mea

sure

men

tR

ecor

dM

easu

rem

ent

Adj

ustin

g B

olt

Spi

ndle

Nut

Figu

re 8

-20

Mea

sure

men

t for

Spi

ndle

Nut

and

Ad

just

ing

Bol

t

8-66



CAUTION: Release the spring load by loosening the adjusting bolt nut (21) and then theadjusting bolt (20) by turning them counter clockwise before loosening the bonnet stud nuts.

6. Remove the bonnet stud nuts (19) holding the bonnet (17) to the body (1). Lift thebonnet up to clear the spindle (14) and spring (15). Be sure that the bellows adapterflange (5D) is not stuck in the bonnet.

7. Remove the spring (15) with its spring washers (16) from the spindle (14) and keepthem as a unit.

8. Lift as a unit the spindle (14), bellows assembly (5), disc insert (6), disc insert andring pin (7), and disc ring (8) out of the guide (13).

9. The spindle (14) can be separated from the assembly by screwing it out of the discholder (5B) using a slight upward force to engage the disc holder threads.

10. The disc holder (5B), disc insert (6), and disc ring (8) are held together by means ofthe disc insert and ring pin (7). To remove the disc insert for lapping or replacement,it is necessary to drive the pin out to separate the pieces.

11. Visually inspect the seating surface of the disc for scratches, nicks, or indentationscaused by foreign matter in the service fluid. The seating surface should be lappedin accordance with the procedures described in Section 8.4.1.

12. Remove the guide (13) from the body (1).

13. Remove the nozzle ring (3) by screwing it off the nozzle (2).

14. Unless the seat on the nozzle (2) is severely damaged, it will not be necessary toremove the nozzle from the body (1). If repair is necessary, the nozzle seat can usu-ally be lapped in place. To recondition the seat, it may be easier to remove the nozzle

15. Visually inspect the seating surface of the nozzle for scratches, nicks, or indentationscaused for foreign matter in the service fluid. The seating surface should have amirror finish. If the nozzle seat requires machining or lapping, it will be necessary toremove the nozzle from the body (1) by unscrewing it. Remove the inlet studs (52)before unscrewing the nozzle. The seating surface should be lapped in accordancewith the procedures described in Section 8.4.1.

16. If it is necessary to replace the O-ring in the cap and lever assembly, remove thelever pin (34) and back out the dog cam bearing (30).

8-67



8.11.3 Assembling Auxiliary PRVs

General

Prior to any assembly operation, the valve seats should be relapped and other partsreconditioned, cleaned, lubricated, and then assembled. This is accomplished as follows:

1. Thoroughly clean all parts by an approved cleaning method. A fine emery cloth orcrocus cloth may be used to clean guiding surfaces and surfaces in intimate rubbingcontact. Care must be exercised to insure that the dimensions of these surfaces arenot affected.

2. Examine all gasket sealing surfaces as well as the gaskets themselves. If necessary,polish sealing surfaces and replace defective gaskets.

3. The disc and nozzle seating surfaces should be examined for nicks or marks thatcould effect valve seating. If these surfaces are not flat and free from defects, thesurfaces should be lapped in accordance with the manufacturer’s recommendedprocedures.

4. The following areas should be lubricated prior to assembly: 1) on the bonnet and capstud and nut threads as well as the washer face of the nuts, use Never-Seez (purenickel special number 165) nuclear grade or equivalent; on all locations, excludingthose specified in the assembly procedure, use Dow Corning 41 or equivalent.

8.11.4 Assembly

The assembly drawing for the particular valve being assembled should be on hand.Assembly is essentially the reverse of disassembly, but certain steps and precautionsmust be observed.

CAUTION: To ensure proper valve operation, care must be taken to accurately set theadjusting rings (nozzle ring) to the measurement recorded during disassembly. If the correctsetting of the adjusting rings is questionable for any reason, the valve document packageshould be consulted. If the document package is not available or further difficulty is encoun-tered, contact the manufacturer.

1. If the nozzle was removed for lapping, lubricate the nozzle threads and the nozzlebackface. Screw the nozzle into the body and tighten by hand until the nozzlebackface is firmly seated. Lubricate and install the inlet studs (52).

2. Screw the nozzle ring (3) onto the nozzle (2) until the seating plane of the nozzleextends above the guide diameter of the nozzle ring.

3. Place the disc insert (6) in the disc holder (5B) and install the disc insert pin (7). Placethe disc ring on the disc holder (5B).

8-68



4. Lubricate both sides of the guide gasket (26) and place on the body (1). Lower theguide (13) into the body (1).

5. Lubricate both sides of the bellows adaptor gasket (24) and place on the top of theguide (13). Lower the bellows and disc holder assembly into the body taking care toalign the disc ring (8) into the nozzle ring (3).

6. Lubricate the spindle ball and install the spindle (14) into the back end of the discholder (5B).

7. Lubricate the spring washer beveled bearing surfaces and install the spring (15) andspring washer (16) on the spindle.

8. Lower the bonnet (17) into place using care to prevent any damage to the seats orspindle. The bonnet must be located and seated on the bellows adaptor flange (5D)and must be evenly tightened down as follows:

9. With the bonnet in place, lubricate the stud threads, nut threads, and nut washerfaces with an approved thread lubricant.

10. Install the nuts on the studs finger-tight.

11. Tighten the nuts in the sequence shown in Figure 8-21 below to approximately one-half the minimum torque value shown on the data sheet drawing. Repeat the samesequence of tightening to 0.75 times the minimum required torque value. Then,starting with the number 1 nut, tighten each nut in order in a clockwise or counterclockwise direction to a value no greater than the maximum torque value shown onthe data sheet drawing.

1

34

2

1

3

4

2

5

6

Figure 8-21Typical Bonnet Assembly Torque Sequence

12. Lubricate the adjusting bolt (20) threads and radius that contact the upper springwasher bearing surface. Lubricate the adjusting bolt nut (21) threads and bearingsurfaces and screw the two parts together. Install both parts in the bonnet (17).Tighten the adjusting bolt to its approximate original position.

13. Adjust the nozzle ring to its original position.

14. Lubricate the set screw gasket (23) and install the set screw (4) and gasket (23). Caremust be taken to engage one of the slots in the nozzle ring. The set screw mustengage but not bear on the nozzle ring.

8-69



15. Screw the spindle nut (36) onto the spindle (14) to its approximate original position.Install the spindle nut cotter pin (37) and bend the tabs.

16. Lubricate both sides of the cap gasket (28) and place on the bonnet.

17. Lubricate the threads on the cap and screw the cap (27) onto the bonnet (17).

18. Lubricate both sides of the cap plug gasket (39) and install the cap plug gasket andcap plug (38).

19. Install the O-ring (32) in the dog cam (29). Slide the dog cam bearing (30) over the O-ring followed by the lever pin spacer (38). Slide the lever (33) over the dog cam (29)and pin the assembly. Lubricate the dog cam bearing gasket (31) and slip the dogcam (29) into the cap (27). Put the lever in the exact vertical position and tighten thedog cam bearing.

20. The spindle nut (36) may need to be adjusted at this point. The dog cam (29) mustnot bear on the spindle nut when the lever is in the vertical position but the valvesmust open when the lever is rotated upward.

The valve is now ready for test. Partial disassembly may be necessary during the testsequence to allow for adjustments.

8.11.5 Troubleshooting

Tables 8-10a and 8-10b show typical problems and corrective actions for auxiliary reliefvalves:

Table 8-10aOperational Problems for Auxiliary Relief Valves

Problem Possible Cause Corrective Action

Set pressure too high or too low Set pressure not correctly set Reset valve

Set pressure verification Loose adjusting bolt nut Reset valve and tightenadjusting bolt locknut

Valve will not close Dog/spindle nut interference Adjust spindle nut

Overpressure too high, reseatpressure too low

Ring(s) not properly adjusted Reset ring(s) to “as-shipped”position

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Table 8-10bSeat Leak Problems for Auxiliary Relief Valves

Problem Possible Cause Corrective Action

Excessive leakage Dog/spindle nut interference Adjust spindle nut

Foreign matter between seats Operate valve with lifting lever at apressure no less than 75% of valveset pressure

Damaged seats Relap seats or replace pieces

Seats not properly lapped Repair or replace pieces (nozzleand/or disc)

Bonnet not positioned correctly onguide or body

Disassemble, then properlyreassemble

Body-to-bonnet leakage Damaged gasket Replace gasket

Unequal torquing of bonnet studnuts

Retorque bonnet stud nuts

8.12 Summary

In this maintenance section of the guide, a broad overview of the maintenance activitiesof PRVs is provided. Hopefully, the guide has provided enough information for thereader to understand the importance of a maintenance program and the critical part itplays to assure satisfactory performance of PRVs. It can only reiterate how important itis to use the valve manufacturer as the primary source for information and for person-nel to apply and use the information correctly.

9-1



9TRAINING AND PERSONNEL QUALIFICATIONS

9.1 Codes and Standards for Training

The codes are not specific as to all the elements necessary for an adequate personneltraining and qualification program for safety valve testing and maintenance personnel.The individual facility is allowed to develop and implement their own training pro-gram. Subsequent sections will outline the basic elements of an adequate training andqualification program.

The addition and addenda of ASME Section XI applicable to the plant’s inservice testingprogram plan ultimately determines whether OM-1-Appendix I, OM-1-Part-13 or ASME-PTC 25.3 (1988) are used as the basis for the pressure valve relief testing and trainingrequirements. Later editions (1989) of the Code refer the user to OM-1-ISTC and OM-1Appendix I to prescribe testing frequencies and requirements. For earlier editions of theCode, both Section XI and PTC-25.3 must be used. Utility personnel should also refer totheir technical specification requirements to determine any additional considerationsabove and beyond code requirements. Additionally, when using Appendix I, personnelshould recognize the limitations described in the document and consider other tests orprocedures to verify the operability of PRDs. Appendix I is not intended to demonstrateconformance with design requirements or verify all aspects of pressure relief operation.OM-1-Part-13 also provides recommendations for testing of PORVs that are not requiredfor system overpressure protection and not tested according to OM-1-Appendix I.


9.1.1 PTC-25.3 Training and Qualification RequirementsPTC-25.3 (1988) in the Code introduction states that it covers the methods and proce-dures to determine relieving capacity and other operating characteristics required forcertification. It does not identify specific training requirements for personnel conductingmaintenance or testing on safety or relief valves. However, stringent responsibilitiesand accountabilities are identified for the testing supervisor certification and can beused as a guide for maintenance personnel. For example, the person supervising thetesting is solely responsible for all aspects of the testing process and should be presentat all times during the test.

PTC-25.3 does require that the person supervising the test must have the followingeducation and experience:

• A formal education in thermodynamics and fluid mechanics

• At least 2 years practical experience in fluid flow measurement

9-2



• Experience in test supervision

In addition, the supervisor should have sufficient training to ensure that:

• All who are involved in taking readings, making pressure and temperature adjust-ments, or any other function that affects test accuracy are fully informed as to thecorrect method of performing such tests

• The written test procedures are followed

• All instruments used in the test are properly calibrated

• Sign and date the test results, thereby verifying to the best of the tester’s knowledgethat the tests are accurate and were conducted in accordance with written test proce-dures

9.1.2 OM-1 Training and Qualification RequirementsThe valve owner is responsible for the qualifications of personnel who perform testingand maintenance when conducting activities within the scope of ASME Section XI,OM-1, Appendix I. Testing and maintenance shall be performed in accordance with theowner’s QA program. This appendix also describes inspections and examination meth-ods that may require other qualifications and certifications to satisfy the owner’s QAprogram.

Additionally, the test supervisor shall have adequate training to ensure that:

• Personnel involved in recording data, making adjustments, or performing anyfunction that affects the accuracy of the test results are informed of the correct meth-ods of performing such functions

• Instrument calibrations are current

• Written procedures used to conduct testing are complied with

• Test results are signed and dated to certify that the tests are accurate and wereperformed in accordance with the written test procedure

9.2 The NBBI

The National Board of Boiler and Pressure Vessel Inspectors (NBBI), located in Columbus,OH, is a non-profit organization comprised of the Chief Inspectors of the jurisdictionsthroughout the U.S. and Canada. Its primary objective is to promote boiler and pressurevessel safety through the administration and enforcement of a uniform set of laws, rules,and regulations covering all aspects of boiler and pressure vessel design, installation,operation, and maintenance. To that end, the Executive Committee of the NBBI autho-rized the development of rules and procedures for the repair and testing of PRDs installedon ASME Code boilers or pressure vessels. The first set of PRD rules and procedures wasissued on January 26, 1977, and has evolved into the current revision of NB-65, NBBI PRVRepair Symbol, Administrative Rules and Procedures.

NB-65 applies to the repair of NBBI capacity certified ASME Code Section I (“V”stamped), Section IV (“HV” marked), and Section VIII (“UV” stamped) PRVs.

9-3



The rules and procedures of NB-65 may be used as a guide and/or extended to apply tothe repair of ASME Code Section III, Class 1, 2, or 3 PRDs that have been capacity certifiedby the National Board. The NR stamp may also be required when repairing and testingASME Section III PRDs.

A copy of NB-65 can be obtained from the NBBI at 1055 Crupper Avenue, Columbus,OH, 43229-1183, USA.

9.2.1 NB-65 Training and Personnel QualificationsNB-65 provides rules and procedures for the training and qualification of personnelinvolved in the repair and testing of PRDs. The following key elements are prescribed:

• Indoctrination

• Training

• Qualification

• Certification

• Evaluation

• Documentation

It is the responsibility of the repair organization to ensure that their personnel are knowl-edgeable and qualified within the scope of repairs to be conducted). The repair organiza-tion is responsible for providing a written in-house training program that establishes thetraining objectives and the method for evaluating training effectiveness. Minimum train-ing objectives shall include:

• Applicable ASME Code requirements

• Responsibilities within the organization’s QC system

• Knowledge of the technical aspects and mechanical skills for the applicable positionheld

The repair organization is responsible for establishing the minimum qualifications forthe positions within the organization as they directly relate to PRV repair and testing.ANSI-N45.2.6 and USNRC Regulatory Guide 1.58 can provide the basis for an adequatepersonnel certification program. Documentation of the evaluation and acceptance ofeach individual’s qualification is required. The repair organization shall also annuallydocument and review personnel qualifications to verify proficiency as well as compli-ance with the certificate holder’s QC system. The review shall include training records,documented evidence of work performed, and, when necessary, monitoring job perfor-mance.

9.2.2 Repair Facility CertificationSome state laws require certification of the safety and relief valve repair facilities.

9-4



The jurisdiction in which the facility is located determines the necessity of obtaining andmaintaining the VR or NR symbol stamp. Utilities are encouraged to contact their chiefboiler and pressure vessel inspector to verify applicable requirements for nuclear facilities.

Authorization to use the VR or NR symbol stamp is granted when a Certificate of Autho-rization is issued by the National Board. The certificate indicates the authorization torepair ASME Section I, III, IV, and/or VIII valves as applicable pursuant to the certifi-cate holder’s QC system. The certificate holder’s QC system designates the scope andtype of valve repairs, the location where the repairs are to be conducted (shop or bothshop and field) and test media. The QC system must specifically address special pro-cesses such as machining, welding, post-weld heat treatment, and NDE. Additionally,the types and size of valves, pressure ranges and other limitations, such as engineeringcapabilities and test facilities, are addressed.

The VR symbol stamp may only be applied to valves that are:

• Stamped with the ASME “V”, “UV”, or “NV” code symbol and have been capacitycertified by the National Board

• Disassembled, inspected, and repaired by the repair certificate holder such that thevalve’s condition and performance are equivalent to the standards for new valves

CAUTION: Utilities located in jurisdictions requiring the use of the VR symbol stampshould note that a PRD meeting all as-found OM-1 Appendix I test requirements may not beacceptable for return to service until the second condition is met.

9.3 Site Training and Personnel Qualifications

NB-65 provides an effective training and qualification program that utilities shouldconsider using as a basis for training personnel involved in the repair and testing ofPRDs. For utilities in jurisdictions requiring the “VR” symbol stamp, the training andqualification program is mandatory. Some jurisdictions may allow the use of 10CFR50Appendix B and its referenced standards because of the generally more restrictivenature of federal regulations enforced by the USNRC. Additionally, some jurisdictionsdefer regulation of the facility exclusively to the USNRC.

9.3.1 Program ElementsElements of effective site training programs for personnel involved in the repair andtesting of PRDs should include consideration of the factors cited in NB-65. Several utilitieshave attended seminars conducted by the NBBI and various valve manufacturers as partof their training programs. This supplemental training is especially effective for personnelengaged in the repair and engineering aspects of PRDs. The NBBI encourages repairorganizations to attend these seminars to supplement in-house training programs.

Program elements should include the following key areas:

9-5



• Training of personnel in the applicable ASME Code requirements, responsibilitieswithin the organization’s QA program and knowledge of the technical aspects, andmechanical skills required to repair and test PRDs.

• Documentation of training including the date of training, attendees, instructor(s),training hours, and the topics covered.

• Qualification and certification of personnel including the objective and subjectiveattributes used by the utility to qualify and certify personnel to repair and test PRDs.

Documentation includes the following:

• The utility program should provide documented training to craft and engineeringpersonnel performing PRD repair and testing.

• Training materials should be reviewed annually for adequacy and revised whenappropriate. Operating Experience Review Program items should be routed to thetraining department for inclusion in training material when appropriate.

• Craft and technician qualifications should be maintained and reviewed to ensure thatonly trained individuals are performing PRD repair and testing. Although craft quali-fications are required to be reviewed prior to a work task assignment, it is suggestedthat the craft and technician qualifications be reviewed at least 12 weeks prior to anysafety and relief valve testing. This allows time for training departments to conductany relevant additional training.

• A list of qualified technical, maintenance, or engineering management personnelshould be maintained and periodically reviewed to ensure that only trained indi-viduals supervise setpoint testing, review and approve test procedures or disposi-tion the results of tests.

A successful site training program for maintenance personnel, engineering, and otherpersonnel should ensure that:

• Craft and engineering personnel who perform safety valve maintenance and testingreceive training commensurate with their duties.

• Existing valve training classes are reviewed for adequacy in dealing with safetyvalve issues and revised as appropriate.

• Craft qualification for safety valve related tasks are reviewed to ensure that onlycraftsmen trained for the tasks are used.

• Test procedures should list engineering or other personnel who are qualified tosupervise setpoint testing and sign-off test acceptance.

Utilities should also consider training requirements for stores and QA personnel in theirprograms. Shipping and handling practices, proper storage of PRDs, and receipt inspec-tion procedures and methods can directly impact a PRD testing program.

9.3.2 Training AidsFacilities to support safety and relief valve testing and maintenance training are keyconsiderations in obtaining safe, efficient, and high-quality testing and maintenance

9-6



training. Considerations for these facilities and training aid equipment should includethe following:

• Training class size (4 to 6 personnel)

• Type of training (for example, lecture or hands-on)

• Use of mockups

• Environmental controls

• Services (for example, electricity, air, water, gas, etc.)

• Training equipment

Training mockups can also be used for test procedure validation and ALARA concernswhen preparing for critical work on valves.

9.3.3 On-the-Job Training (OJT)This aspect of an individual’s training is normally done in the plant as part of day-to-day work activities. OJT provides hands-on experience that cannot be gained from atextbook or training class. It is essential that skills embodied in experienced craftsmenbe passed along to lesser skilled craft personnel. A formal OJT training program assuresthat skills-of-the-craft are not lost. Accordingly, maintenance department supervisorsand selected qualified and experienced craftsmen are directly involved in OJT.

OJT should be conducted in accordance with formally defined training programs thatspecifically identify items the trainee must accomplish. Knowledge requirements foreach item as well as what the trainee must do (perform, simulate, observe, or discuss)should be defined.

OJT should be conducted by personnel who have successfully qualified as OJT trainers.Personnel with maintenance experience in the training department, as well as personnelin the maintenance department itself, may be used as OJT trainers. These trainersshould have good verbal communication skills, technical knowledge, and the ability toeffectively provide trainees with hands-on experience.

It is incumbent that the OJT trainer promptly update the craft personnel’s trainingrecords to assure that the OJT training is documented so that the craft can be assignedwork tasks without lost time searching for qualification records.

When trainees perform maintenance on equipment, a qualified OJT instructor shouldobserve the work so that the trainee properly accomplishes the activity and understandshow to avoid errors that could affect personnel safety or adversely impact the plant.

The cognizant manager should establish a policy that allows trainees to independentlyperform maintenance only on station equipment for which they are qualified. Thispolicy should specify how supervisors are to ensure a trainee has completed neededtraining requirements before the craftsman is assigned a task to independently performon that equipment.

9-7



Prior to a craftsman being allowed to perform independently, he/she must be certifiedas qualified. This certification requires that the following be addressed:

• Verify that all designed training is complete.

• Conduct or evaluate the results of a final written, oral, or practical demonstrationexamination and evaluate the recommendations of the individual supervisor.

• Resolve all discrepancies concerning the craftsman’s qualifications.

• Provide formal qualification approval and documentation.

In conjunction with the Site Training Department requirements, the qualified OJT trainermaintains an up-to-date record of each craftsman’s OJT training experiences and providesOJT records to the Site Training Department. Without these training records, the crafts-man will not be allowed to independently perform required facility maintenance.

10-1



10INDUSTRY DATA AND CONTACTS

The main purpose of this section is to provide a reference for engineers and mainte-nance supervisors to use as a source book for specific contacts and data applicable tosafety and relief valves used in nuclear power plants. The information contained in thissection is for reference only and in no way constitutes an endorsement of their servicesby EPRI or NMAC. There may also be other manufacturers/suppliers not listed here.Maintenance and utility personnel requiring specific testing and valve informationshould obtain that information by contacting the test facility or valve manufacturer.

This section also provides a listing of contacts for valve testing facilities, valve manufac-turers, and ALD manufacturers. In addition, applicable data and applications forunique safety relief valve types are identified. Utilities that have testing facilities canprovide valuable data and information and should be contacted.

The testing facilities identified offer a wide variety of testing options, steam and fluidconditions to satisfy code testing requirements.

10.1 Safety and Relief Valve Testing Facilities

Testing is a requisite to confirm the reliability of primary safety and secondary systemsafety, safety relief, and relief valves.

10-2



Table 10-1 below identifies domestic testing facilities that have a broad range of testingcapabilities from full-flow testing to limited volume. It is recommended that the specificfacility be contacted for their total test capability.

Table 10-1Safety and Relief Valve Testing Facilities

Wyle Laboratories1841 Hillside AvenueNorco, CA 91760(909) 737-0871

Wyle LaboratoriesP. O. Box 0777777800 Highway 20 WHuntsville, AL(205) 837-4411

Duke Power CompanyMarshall Steam StationTerrell, NC(704) 875-4866

Crosby Valve and Gage Company43 Kendrick StreetWrentham, MA 02093(508) 384-312

National Board of Boiler and Pressure Vessel InspectorsNational Board Testing Laboratory7437 Pingue DriveWorthington, OH 43085(614) 888-8320

10.2 Safety and Relief Valve Manufacturers

Table 10-2 identifies valve manufacturers who are currently supplying and servicing safetyand relief valves in the United States. Valves from other manufacturers may be found insome nuclear power plants in the US. However, these companies are either no longerproviding services, have contracted with other manufacturers to provide service for them,or their product has been acquired by one of the manufacturers listed in Table 10-2.

10-3



Table 10-2Safety and Relief Valve Manufacturers

Control Components Inc.22591 Avendia EmpresRancho Santa Maria, CA(714) 858-1877

Copes-VulcanP. O. Box 577Lake City, PA 16432(814) 774-1500

Crosby Valve and Gage Company43 Kendrick StreetWrentham, MA 02093(508) 384-3121(Also manufacture and support GarrettPORV)

Dresser Industrial Valve OperationP. O. Box 1430Highway 71 NorthAlexandria, LA 71309-1430(318) 640-2250

Fisher Controls Company205 South Center StreetMarshalltown, IA 50158(515) 754-3011

Masoneilan85 Bodwell StreetAvon, MA 02322(508) 586-4600

Target Rock Corp.1966 E. Broadhollow RoadE. Farminghdale, NY(516) 293-3800

Anderson GreenwoodP. O. Box 944Stafford, TX 77497(713) 274-4400

Dikkers (out of business)Contact:GE Nuclear Energy175 Curtner AvenueMail Code 753San Jose, CA 95125(408)-925-1000(Contact GE site representative, if available)

10-4



10.3 ALD Manufacturers

The use of ALDs is becoming an important maintenance tool in the ISI programs ofmany facilities. This versatile testing tool allows for testing in non-hostile environments,does not affect subsequent valve performance, minimizes testing expenses and man-power requirements, and fully complies with the accuracy requirements of the ASMEOM-1 Code. Table 10-3 is a listing of ALD suppliers.

Table 10-3ALD Suppliers

ALD System (or Trade Name) Supplier

Trevitest Furmanite Incorporated2645 International ParkwayVirginia Beach, VA 23452(804) 427-1991

Electronic Valve Testor (E.V.T.) Dresser Industrial ValveP. O. Box 1530Highway 71 North Alexandria, LA 71309-1430(318) 640-6046

Set Pressure Verification Device (S.P.V.D.)

Air Set Pressure Device (ASPD)

Hydraulic Set Pressure Device (HSPD)

Crosby Valve & Gage Co.43 Kendrick StreetWrentham, MA 02093(508) 384-3121

Ultrastar A.V.K. Industries8640 Phillips HighwayJacksonville, FL 32256(904) 733-9887

10-5



10.4 Safety and Relief Valve Types, Applications, and Distribution

The tables that follow are designed to provide information on safety and relief valveinstallations at various domestic and international nuclear power plants. They providean overview of a product’s installed base for a particular manufacturer.

Table 10-4Pressurizer Safety Valves and Distribution in PWR Plants

Size*

Valve Manufacturer Model Inlet Orifice Outlet No. of Plants

Crosby Valve & GageCo.

HB-BP-86 334646466

KK2K2K2M1M1MMN

666666668

3262361386

Dresser Industries 31709KA31739A31749A31759A31709NA

2.52.5336

KNo.3No.4No.5N

66668

1113517

Target Rock Corp. 69C 6 3.513

in26 1

*Inlet and outlet sizes are nominal pipe sizes in inches.

10-6



Table 10-5Power-Operated Relief Valve Distribution in PWR Plants

Valve Manufacturer Model Size* No. ofPlants

Control Components Drag Valve 3-in NPS 4

Copes-Vulcan Globe D-100-160with 17-4PH cage andplug

Globe D-100-160 with316 w/Stellite plug and17-4PH cage

Globe D-100-160 with316 w/Stellite plug andHaynes #25 cage

2-in NPS

3-in NPS

3-in NPS

13

23

2

Crosby Valve & Gage Co. HPV-SN 1-3/8-in bore1-1/2-in bore

21

Dresser Industries 31533VX-30

31533VX

1-3/32-in bore1-5/32-in bore1-5/16-in bore

1-3/8-in bore

63

11

1

Fisher Controls Co. SS-103-SS-95 3-in NPS 3

Garrett Pneumatic SystemsDivision (Product lineacquired by Crosby Valve &Gage Company)

Angle

Straight-through

3-in inlet8-in outlet

3-in inlet6-in outlet

1

**

Masoneilan 20,000 series 2-in NPS 9

MUESCO Controls, Inc. 70-18-9-DRTX 2-in NPS 1

Target Rock Corp. 80X-006 2-1/2-in inlet4-in outlet

2

*NPS is the valve's nominal pipe size.**Data not available.

10-7



Table 10-6Crosby MSSV and PSV Installations at Domestic and International Utilities

Utility Station Style/Model #

Size ReactorMFG

(note 4)

TypeReactor

and Rating

Loop

Alabama PowerCo.

Joseph M. FarleyUnits 1 & 2

HB-BP-86 6M16 W829 MW

PSV

EntergyOperations Inc.

Arkansas NuclearUnit 2

HB-BP-86 6M6 CE BWR858 MW

PSVMSSV

Carolina Power &Light

Shearon HarrisUnits 1 & 2

HB-BP-86 6M6 W PWR900 MWeach

PSVMSSV

Robinson Unit 2 HB-BP-86 4K26 W PWR665 MW

PSVMSSV

CommonwealthEdison

BraidwoodUnits 1 & 2

HB-BP-86 6M6 W1120 MW

PSV

Byron Units 1 & 2 HB-BP-86 6M6 W1120 MW

PSV

LaSalleUnits 1 & 2

HB-BP 6R10 GE BWR1078 MWeach

MSSV

Zion Units 1 & 2 HA-65 6R10 W PWR1040 MWeach

MSSV

ConnecticutYankee AtomicPower

Haddam NeckUnit 1

HB-BP-86HA-65

3K66R10

W PWR582 MW

PSVMSSV

ConsolidatedEdison

Indian PointUnit 1(Retired fromService in 1980)

-- -- BW PWR265 MW

PSVMSSV

Indian PointUnit 2

HB-BP-86 4M6 W PWR873 MW

PSVMSSV

Consumers Power Big Rock PointUnit 1

GE BWR63 MW

MSSV

PalisadesUnit 1

HA-65 6R10 CE PWR740 MW

MSSV

Duke Power Co. McGuireUnits 1 & 2


PSVMSSV

OconeeUnits 1 & 2

HA-65 6R10 BW PWR860 MW

MSSV

Duquesne LightCo.

Beaver ValleyUnits 2

HB-BP-86HA-65

6M166R10

W PWR833 MWeach

PSVMSSV

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Table 10-6Crosby MSSV and PSV Installations at Domestic and International Utilities (cont.)


Size ReactorMFG

(note 4)

TypeReactor

and Rating

Loop

Shippingport (to bedecommissioned in1984)

-- -- W60 MW(pre-code)

PSV

Florida Power &Light Co.

St. LucieUnits 1 & 2

HB-BP-86 3K6 CE PWR839 MWeach

MSSV

Turkey PointUnits 3 & 4

HB-BP-86 4K26 W666 MW

PSV

Georgia Power Co. VogtleUnits 1 & 2

HB-BP-86HA-65

6M66R10

W PSVMSSV

Gulf States UtilitiesCo.

River BendUnits 1 & 2

HB-BP 6M6 GE BWR940 MWeach

MSSV

Houston Lighting& Power Co. andOthers

South TexasProjectUnits 1 & 2

HB-BP-86 6N8 W1250 MW

PSV

Indiana &Michigan ElectricCo.

Donald C. CookUnits 1 & 2

W1054 MWand 1094MW

PSV

Wolf CreekOperating Co-op

Wolf CreekUnit 1


PSVMSSV

EntergyOperations Inc.

WaterfordUnit 3

HA-65-FN 8T10 X10

CE PWR1104 MW

MSSV

Maine YankeeAtomic Power Co.

Maine YankeeUnit 1

HA-65 CE PWR825 MW

MSSV

Northeast Utilities MillstoneUnit 3

HB-BP-86 6M6 W1150 MW

PSV

Northern StatesPower Co.

Prairie IslandUnits 1 & 2

HB-BP-86 6M16 W520 MW

PSV

Omaha PublicPower District

Fort CalhounUnit 1

HB-BP-86 3K6 CE478 MW

PSV

Pacific Gas &Electric Co.

Diablo CanyonUnits 1 & 2

HB-BP-86 6M6 W 1084 MWand1106 MW

PSV

Power Authority ofthe State of NewYork

Indian PointUnit 3

HB-BP-86HA-65

6M66R10

W PWR965 MW

PSVMSSV

PennsylvaniaPower & Light Co.

SusquehannaUnits 1 & 2

HB-BP-65 6R10 GE BWR1050 MWeach

MSSV

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Size ReactorMFG

(note 4)

TypeReactor

and Rating

Loop

Public ServiceElectric & Gas Co.

SalemUnits 1 & 2

HB-BP-86HA-65

6M66R10

W PWR1090 MWand 1115MW

PSVMSSV

New HampshireYankee

SeabrookUnits 1 & 2 (note 1)

HB-BP-86HA-65

6M66R10

W PWR1150 MWeach

PSVMSSV

Rochester Gas &Electric Co.

GinnaUnit 1

HB-BP-86HC-65

4K266R10

W PWR490 MW

PSVMSSV

South CarolinaElectric Co.

Virgil C. SummerUnit 1

HB-BP-86 6M6 W900 MW

PSV

SouthernCalifornia EdisonCo.

San Onofreunits 2 & 3

HA-65 6R10 CE PWR1100 MEeach

MSSV

SouthernCalifornia EdisonCo. and SanDiego Gas &Electric Co.

San OnofreUnit 1

HB-BP-86 3K26 W 436 MW PSV

Tennessee ValleyAuthority

SequoyahUnits 1 & 2

HB-BP-86HA-65

6M66R10

W PWR1148 MEeach

PSVMSSV

Watts BarUnits 1 & 2

HB-BP-86HA-65

6M66R10

W1177 MW

PSVMSSV

Texas UtilitiesGenerating Co.

Comanche PeakUnits 1 & 2

HB-BP-86 4M16 W PWR1150 MWeach

PSVMSSV

Toledo Edison Co. Davis BesseUnit 1

HB-BP-86 4M16 BW906 MW

PSV

Union Electric Co. CallawayUnit 1

HB-BP-86 6M6 W PWR1150MW

PSVMSSV

Virginia Electric &Power Co.

North AnnaUnits 1 & 2

HB-86-BP 6M6 W PWR865 MWand890 MW

MSSV

SurryUnits 1 & 2

HB-BP-86 6K26 W775 MW

PSV

Wisconsin ElectricPower Co.

Point BeachUnits 1 & 2

HB-BP-86 4K26 W PWR497 MWeach

PSVMSSV

Wisconsin PublicService Corp.

KewauneeUnit 1

HB-BP-86 6M16 W535 MW

PSV

10-10





Size ReactorMFG

(note 4)

TypeReactor

and Rating

Loop

ELECTRABELBelgium

DoelUnits 1 & 2

N.A. N.A. A(Belgium

/West)390 MW

PSV

ELECTRABELBelgium

DoelUnit 3

N.A. N.A. F PWR900 MW

PSVMSSV

DoelUnit 4

N.A. N.A. A PWR1000 MW

PSVMSSV

ELECTRABELBelgium

TihangeUnit 1

N.A. N.A. F900 MW

PSV

TihangeUnit 2

N.A. N.A. A1000 MW

PSV

Furnas CentraisElectriacs SA, Brazil

AngoraUinit 1

N.A. N.A. W PWR626 MW

PSVMSSV

Ontario Hydro -Canada

PickeringUnits 5,6,7 & 8

N.A. N.A. AECL PHWR516 MWeach

MSSV

Electricite deFrance (EdF)

FessenheimUnits 1 & 2

N.A. N.A. F/C-L890 MW

PSV

(Valves supplied by Crosby Licensee in France)

TricastinUnits 1, 2, 3, &4

N.A. N.A. F/C-L920 MW

PSV

(Valves supplied by Crosby Licensee in France)

Nuclear PowerCorp. (India)

TarapurUnits 1 & 2 (note 2)

N.A. N.A. GE BWR200 MWeach

MSSV

Kansai ElectricPower Co. - Japan

MihamaUnit 1

N.A. N.A. W320 MW

PSV

OHIUnits 1 & 2

N.A. N.A. W1120 MW

PSV

TakahamaUnit 1

N.A. N.A. W780 MW

PSV

Korea ElectricPower Corp. Korea

KO-RIUnit 1

N.A. N.A. W 564 MW PSVMSSV

KO-RIUnit 2


PSVMSSV

Comision Federalde Electricidad(CFE) - Mexico

Laguna VerdeUnits 1 & 2

N.A. N.A. GE BWR654 MEeach

MSSV

10-11





Size ReactorMFG

(note 4)

TypeReactor

and Rating

Loop

National PowerCorp. Phillipines

PNPPUnit 1


PSVMSSV

Central Nuclear deAlmaraz, S.A. -Spain

AlmarazUnits 1 & 2

N.A. N.A. W PWR930 MWeach

PSVMSSV

Union Electrica SAand FuerzasElectricas delNoroeste, SA -Spain

Jose CabreraUnit 1

N.A. N.A. W153 MW(pre-code)

PSV

Iberdrola, S.A. -Spain

CofrentesUnit 1

N.A. N.A. GE PWR930 MW

MSSV

Central Nuclear deValdecaballeros -Spain

ValdecaballerosUnits 1 & 2


MSSV

Central NuclearVandellos II - Spain

Vandellas II (note3)


PSVMSSV

Vattenfall AB -Sweden

RinghalsUnits 2, 3 & 4

N.A. N.A. W #2: 800MW#3&4:900 MW

PSV

Nordostshweizenische Kraftwerke AG(NOK) - Switzerland

BeznauUnits 1 & 2

N.A. N.A. W350 MW

PSV

Taiwan Power Co. -Taiwan

ChinshanUnits 1 & 2


MSSV

KuoshengUnits 1 & 2


MSSV

MaanshanUnits 1 & 2

N.A. N.A. W PWR907 MWeach

MSSV

NuklearnaElektrarna Krsko(Slovenia)

KrskoUnit 1

N.A. N.A. W615 MW

PSV

10-12




Notes:

1. Manufacturer of Unit 2 valves is “on hold” pending decision by utility to build this unit.

2. Main steam valves manufactured by Crosby USA/Nuovo Pigone, Italy.

3. Main steam valves manufactured by the Crosby affiliate, Walthon Weir Pacific S.A. - Spain

4. Reactor manufacturers shown in Table 10-6 are:

CE—Combustion Engineering AECL—Atomic Energy of Canada

GE—General Electric NIRA—Nucleare Italiana Peacttori Avanzati

B&W—Babcock and Wilcox F—Framaceco

AC—Allis Chalmers A—Acecowen

C-L—Creusot-Loire N.A.—Information Not Available

Table 10-7Nuclear Power Plants with Dresser Pressurizer Safety Valves

Utility Unit Model #

Arizona Public Service Co. Palo Verde 1, 2, & 3 31709 NA

Baltimore Gas & Electric Co. Calvert Cliffs 1 & 2 31739A (Cast, Body, Forged Bonnet)31739A (Forged Body, Forged Bonnet)

Louisiana Power & Light Co. Waterford 3 31809 NA

Maine Yankee Atomic Power Maine Yankee 31709 A

Metropolitan Edison Co. TMI 1 & 2 31739 A (Forged Body, Forged Bonnet)

Northeast Utilities Millstone 2 31739 A (Forged Body, Forged Bonnet)

Portland General Electric Co. Pebble Springs 1 & 2 31709 NA

Sacramento Municipal UtilityDistrict

Rancho-Seco 1(Shut Down)

31759 A (Forged Body, Forged Bonnet)

Southern California Edison Co. San Onofre 2 & 3 31709 NA

Tennessee Valley Authority Bellefonte 1 & 2 31709 NA

Virginia Electric & Power Co. North Anna 1 & 2 31759 A (Cast Body, Forged Bonnet)

Washington Public PowerSupply System

WPPSS 1 & 4 31709 NA

10-13



Table 10-8Nuclear Power Plants Using Target Rock Safety Valves

Site General ElectricP. O. #

General ElectricMPL #

Model 67F (BWR Application)A. Valve Serial Numbers 1 through 129

MillstoneMonticelloPilgrim 1Vermont YankeePeachbottom 2Peachbottom 3Browns Ferry 1Browns Ferry 2Browns Ferry 3FitzpatrickCooperE. I. Hatch 1Brunswick 1Brunswick 2Fukushima 2Dresden 3Quad Cities 1

205AE940, AB841205AE940, AB841205AE940205AE940205AE940205AE940205AE940205AE940205AE940205AE940205AE940205AE940, AB841205AB841205AE940, AB841205AE940205AB841205AB841

203-32-71203-32-712-712-712-712-712-712-712-71B21F013B21F013B21F0132-71203-5203-5

B. Valve Serial Numbers 130 and up

Millstone 1Pilgrim 1Peachbottom 2 and 3Browns Ferry 1FitzpatrickBrunswick 1Dresden 2 and 3Quad Cities 1 and 2Nine Mile Point 1MonticelloFukushima 1Fukushima 2TsurugaNuclenor

205AF791205AF791205AF791205AF791205AF791205AF791205AF791205AF791205AF791205AF791205AF791205AF791205AF791205AF791

203-3203-32-712-712-71B21F013203-5, -7203-5, -71142-71203-5, -82-71203-7203-7

C. Model 7567F (BWR Application)

Fermi 2Hope Creek 1 and 2Cooper " "ShorehamPilgrim 1Peachbottom 2 and 3FitzpatrickBrunswick 1 and 2

205AD140205AD141205AD141205AJ600205AB843205AB845205AJ600205AJ600205AJ600205AJ600205AJ600

B21F013B21F0132-71 " "D21F013203-32-712-71B21F013

A-1



APPENDIX ASAFETY AND RELIEF VALVE MAINTENANCEGUIDELINE REFERENCES

United States Nuclear Regulatory Commission Documents

Information Notices

79-18 Proper Installation of Target Rock Safety Relief Valves80-40 Excessive Nitrogen Supply Pressure Actuates Safety Relief Valve82-41 Failure of Safety Relief Valves to Open at a BWR83-22 BWR Relief Valve Failures83-26 Failure of Safety Relief Valve83-39 Failure of Safety Relief Valves to Open83-82 Failure of Safety/Relief Valves to Open at BWR84-33 Main Steam Safety Valve Failures Caused by Failed Cotter Pins86-05 Main Steam Safety Valve Test Failures and Ring Setting Adjustments86-12 Target Rock Two-Stage PRD Set Point Drift86-56 Reliability of Main Steam Safety Valves Set Point Drift86-92 Pressurizer Safety Valve Reliability87-46 Undetected Loss of Reactor Coolant87-48 Information Concerning the Use of Anaerobic Adhesives/Sealants88-30 Target Rock Two-Stage PRD Set Point Drift Update88-68 Set Point Testing of Pressurizer Safety Valves with Filled Loop Seals Using

Hydraulic Assist Devices89-32 Surveillance Testing of Low-Temperature Overpressure Protection Systems89-90 Pressurizer Safety Valve Lift Set Point Shift89-90 Pressurizer Safety Valve Lift Set Point Shift; Supplement 189-90 Pressurizer Safety Valve Lift Set Point Shift; Supplement 290-06 Power Operated Relief Valve Reliability and Additional Low-Temperature

Overpressure Protection for Light Water Reactors90-11 Maintenance Deficiency Associated with Solenoid Operated Valves91-74 Changes in Pressurizer Safety Valve Set Points Before Installation

A-2



92-61 Loss of High Head Safety Injection92-64 Nozzle Ring Settings on Low Pressure Water Relief Valves92-60 Valve Stem Failure Caused by Embrittlement93-02 Malfunction of a Pressurizer Code Safety Valve

Generic Letters

81-36 Revised Schedule for Completion of TMI Action Plan Item II.D.I Relief andSafety Valves in PWRs

Bulletins and Reports

74-04 Malfunction of Target Rock Safety Relief Valves

74-14 BWR Relief Valve Discharge to Suppression Pool

80-25 Operating Problems with Target Rock Relief Valves at BWRs

AEOD/S92-02 -Special Study- Safety and Safety/Relief Valve Reliability

NUREG-1482, Guidelines for In Service Testing in Nuclear Power Plants

Institute of Nuclear Power Operations (INPO) Documents

Significant Operating Experience Report (SOER)

SOER 81-6 Dresser Safety Valve Blowdown Setting

SOER 81-8 Spurious Actuation of Safety/Relief Valve

SOER 82-9 Ring Settings for Dresser Safety Valves

SOER 82-81 Brazed Spring Guides in Dresser Relief Valves

SOER 83-83 Stress Corrosion Cracking for Pilot Line for Pressurizer Safety Valve

SOER 84-84 Loss of Reactor Coolant Due to Stuck Open Relief Valve andBlocked Valve

Significant Experience Report (SER)

SER 08-80 Main Steam Safety Valve Failed to Reseat

SER 29-80 Valve Disc Guide Cracking Main Steam Safeties

SER 52-80 Main Steam Safety and Reliefs Target Rock

SER 10-81 Failure to Open of Steam Generator Relief Valve

SER 15-81 BWR Electromagnetic Relief Valve Failure

SER 98-81 Two-Stage Target Rock Safety Relief Valves

SER 98-81 Two-Stage Target Rock Safety Relief Valves Set Point Drift; Supplement 1

A-3



SER 98-81 Two-Stage Target Rock Safety Relief Valves; Supplement 3

SER 08-82 Inadvertent Main Steam Insolation Valve Closure

SER 10-82 Steam Generator Tube Rupture with Primary Relief Valve Stuck Open

SER 50-82 Failure of Safety Valves to Lift at Set Pressures During Transient

SER 21-84 Failure of Target Rock Power Operated Relief Valves to Open DuringTesting

SER 58-84 Failure of Main Steam Safety Valve to Reclose

SER 59-84 Out-of-Specification Lift Pressures on Main Steam Safety Valves

SER 14-86 Reactor Coolant System Depressurization

SER 15-86 Inoperability of Trains of the Standby Liquid Control System at BWRsDue to Incorrect Relief Valve Set Points

SER 25-86 Failure of Main Steam Relief Valves to Actuate

SER 26-86 Set Point Drift of Target Rock Two-Stage Safety Relief Valves

SER 26-88 Failure of Safety Valves in Condensate and Feedwater Systems to OpenDue to Bonding of Valve Disc and Seat

SER 5-90 Premature Lifting and Excessive Blowdown of Residual Heat RemovalRelief Valves

SER 20-91 Safety Injection System Degraded Due to Damaged Relief Valves inAlternate Minimum Flow Lines

SER 20-92 Multiple Safety System Malfunctions During Safety Valve Testing

SER 3-92 Loss of Component Cooling Water Inventory Due to Improper ReliefValve Setting

SER 18-92 Loss of Reactor Coolant Due to Malfunction of Pressurizer Safety ValveDuring Load Rejection

Codes and Standards

American Society of Mechanical Engineers

ASME/ANSI PTC 25.3-1988

ASME OM-1990 Code, Appendix I

ASME Boiler and Pressure Vessel Code Sections I, II, III, IV, VIII, and XI, includingAppendices 1994 Issue and Addenda issued February 1995

A-4



Vendor Technical Manuals

Dresser Industries\Consolidated—I&M Electromatic RV Type-1533VX

Target RockI&M SR-Model 7567F&M SR-Model 67F

Crosby Valve and Gage CompanyI&M SR-HB-65-BPBulletin No.100IOM Instruction No. I-1137IOM Instruction No. I-1139IOM Instruction No. I-1105-2Furmanite-Trevitest Apparatus-Operations Manual

Anderson, Greenwood and CompanyBulletin No. 02-400-90Bulletin No. Catalog 3-1900-89

Wyle LaboratoriesTest Procedure No.-1018Test Procedure No.-1016Test Procedure No.-1009Test Procedure No.-1059

EPRI Reports

EPRI NP-2292 PWR Safety and Relief Valve Test Program—Valve Selection/Justification Report

EPRI NP-4306-SR Safety and Relief Valves in Light Water Reactors

EPRI NP-2628 EPRI PWR Safety and Relief Valve Test Program—Safety andRelief Valve Test Report

EPRI NP-2352 Valve Inlet Fluid Conditions for Pressurizer Safety and ReliefValves for Babcock and Wilcox 177-FA and 205-FA Plants

EPRI NP-2296 Valve Inlet Fluid Conditions for Pressurizer Safety and ReliefValves for Westinghouse-Designed Plants

EPRI NP-2318 Valve Inlet Fluid Conditions for Pressurizer Safety and ReliefValves inCombustion Engineering-Designed Plants

EPRI NP-4235 Set Point Testing of Safety Valves Using Alternative Test MethodsEPRI Project 1811-1

A-5



Miscellaneous Publications

Dunn’s Valve Testers Inc. Brochure

Lewis, R.E., P.E. “Safety Valve Set Point Shift due to Temperature.” December 8, 1992

Wade, Jack. “Thermal Profiles and Thermal Effects on Valve Operations.” ENTERGYOperations.

Zahorsky, J.R. “Degradation of Pressure Relief Valve Performance Caused By InletValve PipingConfiguration.”

Shideler, Howard. “Pressure Relief Valve Basics.” Valve Magazine ,Winter 1993.

Thibault, David G. and Zahorsky, John R. .”In-Service Set Pressure Testing of SafetyValves.” Crosby Valve and Gage Company

“ASME Code Safety Valve Rules-A Review and Discussion.” Presented at the SeventhInternational Conference of Pressure Vessel Technology [conference paper].

J. S. Hsieh, D.A. Van Dyne, G. G. Morell, J. R. Zahorsky. ”Effects of Pressure ReliefValve Characteristics on System Operation and Water Hammer Loads.” Presented atthe ASME Annual Meeting, Winter 1987.

B-1



APPENDIX BSELECTION, SIZING, AND INSTALLATION OF PRVS

1.0 Introduction

In selection and sizing of a relief valve it is necessary to determine all potential sourcesof overpressure and then calculate the fluid removal rate under emergency conditionsto maintain the pressure within allowable limits. The ASME Boiler and Pressure Vessel(B&VP) Code provides rules for the design, manufacture, capacity certification, selec-tion, and application of pressure devices used to protect fired and unfired pressurevessels. However, providing adequate overpressure protection is not always clearcut,and the Code rules may differ depending on the type of vessel to be protected. Thisrequires a good working knowledge of the 11 book sections of the ASME B&PV Code,of which 5 sections specifically deal with the requirements for overpressure protection.This discussion will only address Section III—Nuclear Power Plant Components andSection VIII—Unfired Pressure Vessels.

2.0 Overpressure Protection

The principle design basis for pressure vessels is the safe containment of design pres-sure. Protection against overpressure is a very important aspect of pressure vesseldesign. Proper selection, use, location, and maintenance of relief devices are also essen-tial to protect personnel and equipment as well as to comply with codes and laws. Toprovide the protection required, the designer must first determine the consequencesthat could arise in the system from the application of conditions of pressure and coinci-dent temperature that would cause either the design pressure or service limits (speci-fied in the design specification) to be exceeded and the capacity developed as a result ofthis event. The system designer must then provide a sufficient number of relief devicesto furnish a capacity that would mitigate the overpressure condition. The Code is oftenspecific as to the capacity required, but sometimes this capacity is not readily apparent;in such cases, the Code places the responsibility for its determination on the designer.

2.1 Determining Required Relieving Capacity

The design of the proper relieving device must take into consideration all of the follow-ing upset conditions for the individual equipment if such an upset can occur: 1) blockeddischarge; 2) fire exposure; 3) tube ruptures; 4) control valve failure; 5) thermal expan-sion; and 6) utility or auxiliary service failure. Each upset condition must be carefullyevaluated to determine the worst case condition that will dictate the relieving capacity.

B-2



The first step in selecting PRDs for a vessel or system is to determine the required reliev-ing capacity. This requires that all sources of fluid flow and energy into the system beconsidered and evaluated. Sources of energy might be heat, fire, chemical reaction, etc.Sources of fluid flow could include pumps, compressors, stuck open reducing valves,malfunctioning control valves or inadvertent valve operation, failure of an internal heatexchanger tube, or a combination of these types of events. All of these events must betaken into account to determine the worst case overpressure condition. ASME B&VPCode Section III Nuclear Plant Components, Article N(X)7000 provides a comprehensiveset of rules for overpressure protection of nuclear plant components. The rules require ananalysis of all conditions that could cause overpressure and an analysis of pressure tran-sient conditions. The relieving capacity of a safety and relief valve is determined from thisanalysis. For each plant or installation, this analysis is captured in a document known asthe overpressure protection report. This report will also cover the selection of PRDs, theirredundancy and independence under failure conditions.

2.2 System Allowable Valve for Overpressure (Certified Relieving)

PRDs require an increase in pressure above the set pressure to reach a full open posi-tion. The ASME Code provides overpressure values at which PRDs are capacity certi-fied and credited. The Code provides its own rules as to how much the pressure isallowed to increase above the MAWP or design pressure for the particular vessel orsystem during an overpressure event.

Section III limits the overpressure to 10% or 3 psi, whichever is greater, above designpressure for most systems of any component within the systems pressure retainingboundary.

Section VIII limits on overpressure depend on the type of installation. Section VIII man-dates that pressure not be allowed to rise more than 10% or 3 psi, whichever is greater,above MAWP. When multiple devices are used, or additional devices are provided toprotect against exposure to fire, overpressures of 16% or 21% respectively, are allowed.

2.3 Determining Set Pressure

After the relieving capacity and allowable overpressure have been established, the nextstep is to determine the set pressure of the safety and relief valve. The rule for settingsafety and relief valves is that at least one device be set to open at or below the designpressure of the system or vessel being protected. When more than one safety and reliefvalve is used, the additional safety and relief valves may be set at slightly higher pres-sures. This allowable increase in set pressure over MAWP varies throughout the Codedepending on the application and the circumstances as shown in Table B-1. In all cases,the valves must open fully and relieve their (credited) rated capacity at a pressure equalto, or below the system allowable overpressure.

Section III requires at least one PRD to be set at or below the design pressure. Additionaldevices may be set at slightly higher pressures, so long as the maximum overpressuredoes not exceed 10% of the design pressure when all relief devices are discharging.

B-3



Section VIII requires one safety and relief valve be set at or below MAWP. If additionalsafety and relief valves are used, they may be set up to 5% above MAWP. The sectionfurther allows a supplemental valve added to a vessel to protect against hazard due tofire to be set up to 10% above MAWP.

2.4 Set Pressure Tolerances

Each section of the Code provides set pressure tolerances for a myriad of applications.These are also summarized in Table B-1. Note that the set pressure tolerances shown inthe table for ASME Section III Code stamped valves shall apply unless a greater toleranceis established in the overpressure protection report and in the valve design specification.

B-4



Table B-1PRD Operating RequirementsASME Boiler and Pressure Vessel Code Summary

Application Allowable VesselOverpressure

(Above MAWP orVessel Design

Pressure)

SpecifiedPressureSettings

Set PressureTolerance withRespect to Set

Pressure

RequiredBlowdown

Section IIINBNCNDNE

10 % Above thedesign pressure ofany componentwithin the pressureretaining boundaryof the protectedsystem(NB-7311b)(NC-7311b)(ND-7311b)

One valve atdesign pressure

Additional valvesmay be set higherprovided limits onoverpressure aremaintained(NB-7410)(NC-7410)(ND-7410)

Safety Valves± 2 psi for pressures upto and including 70 psi

± 3% for pressuresabove 70 psi up to andincluding 300 psi

± 10 psi for pressuresabove 300 psi up toand including 1000 psi

± 1% for pressuresabove 1000 psi(NB-7512.2)(NC-7512.2)(ND-7512.2) (Note 3)

Safety Valves95% of setpressure(maximum), oras specified indesignspecification(NB-7512.3)

As specified indesignspecification(NC-7512.3)(ND-7512.3)(NE-7512.2)

Overpressure maynot exceed theservice or test limitsspecified in thedesign specification(NE-7110a)

Valves must beset to operatewithinoverpressurelimits(NE-7410)

Safety Relief andRelief Valves± 2% psi for pressuresup to and including 70psi(NB-7513.1a)(NC-7513.1a)(ND-7513.1a)(NE-7512.1a)

± 3% for pressures over70 psi(NB-7513.1a)(NC-7513.1a)(ND-7513.1a)(NE-7512.1a) (Note 3)

Safety Reliefand ReliefValvesAs specified indesignspecification(NB-7513.2)(NC-7513.2)(ND-7513.2)(NE-7512.2)

B-5



Table B-1 (cont.)PRD Operating RequirementsASME Boiler and Pressure Vessel Code Summary



Pressure)



Pressure

RequiredBlowdown

Section III(continued)

Pilot OperatedPressure Relief ValveSame as safety valveabove(NB-7525 b)

Same as safety reliefvalve above(NC-7523.3)(ND-7523.3) (Note 3)

Pilot OperatedPressureRelief ValveSame as safetyvalve(NB-7524)(ND-7525.2)(ND-7524.2)

Power Operated± 1% of set pressure(NB-7532 b1)(NC-7533 b1)

Same as safety valveabove(ND-7533 b1)

PowerOperatedSame as safetyvalve(NB-7532 b2)(NC-7533 b2)(ND-7533 b2)

Rupture Disc± 2% of burst pressurefor pressures up to 40psi(NB-7611)(NC-7612)(ND-7612)

± 5% of burst pressurefor pressures above 40psi(NC-7612)(ND-7612)

B-6



Table B-1 (cont.)PRD Operating RequirementsASME Boiler and Pressure Vessel Code Summary



Pressure)



Pressure

RequiredBlowdown

Section VIIIAll vesselsunless anexceptionspecified

10% or 3 psi -whichever isgreater(UG-125c)

≤ MAWP ofvessel(UG-134a)

± 2 psi up to andincluding 70 psi

None specified

ExceptionsWhenmultipledevicesare used

16% or 4 psi -whichever isgreater(UG-125 c1)

One valve ≤MAWP additionalvalves up to105% of MAWP(UG-134a)

± 3% over 70 psi(UG-134 d1)

Note:Pressure reliefvalves forcompressiblefluids having anadjustableblowdownconstructionmust beadjusted priorto initialcapacitycertificationtesting so thatblowdown doesnot exceed 5%of set pressureor 3 psi,whichever isgreater(UG-131 c3a).This is amanufacturer’scertification testrequirementonly.

Supplement-al device toprotectagainsthazard dueto fire

21% (UG-125 c2) Up to 110%MAWP(UG-134b)

Notes:

1. NB, NE, etc. refers to articles of the Article numbers of the ASME B&VP Codes.

2. The numbers in parentheses reference ASME B&VP Code paragraphs.

3. Set pressure tolerances may be higher if specified in ASME Section III valve designspecification (see Section 2.4 - Set Pressure Tolerances in this appendix).

B-7



2.5 Determining Blowdown

A PRV will generally not reseat until the inlet pressure is reduced to below the setpressure. The difference between actual opening pressure and reseating pressure iscalled blowdown.

Section III allows 5-7% blowdown for safety valves unless a different value is allowedand specified in the valve design specification. For other types of valves, blowdown isspecified in the design specification.

Section VIII has no blowdown requirements for valves as they are shipped from themanufacturer.

3.0 Selecting PRVs

When the required relieving capacity has been established and the allowable set pres-sure and overpressure determined, the pressure relieving devices can then be selected.The choice of device is limited to those permitted by the particular book section cover-ing the service in question.

The PRD most widely accepted by the various book sections of the Code is the spring-loaded PRV. One particular type of spring-loaded valve is the balanced valve, sometimescalled a balanced bellows valve. In this type of valve, a bellows having an effective areaequivalent to the valve seat area is attached to the disc to prevent backpressure in thevalve’s discharge system from acting on the disc. Valves designed under Article NB-7511of ASME Code Section III include a redundant piston in addition to the balanced bellows.

Traditionally, spring-loaded valves for boiler or steam application have been called safetyvalves, spring-loaded valves for liquid application have been called relief valves, and multi-purpose spring-loaded valves that might be used for steam, other compressible fluids, orliquid, have been called safety relief valves. None of these terms fully describes the designor function of a PRV, and in many cases utility personnel tend to use the terms inter-changeably. The more generic term, as defined by the ASME Code, is PRV.

A spring-loaded PRV is permitted by all sections of the Code as an overpressure protec-tion device. Operational and construction requirements, however, vary among the booksections. The popularity of this design is due to the reliability of having few movingparts, the repeatability of an opening point controlled by a spring, and the ability of thevalve to close when an overpressure condition is reduced to a safety level. However,systems with unusual piping configurations, a desire to operate at pressures close tovalve set pressure, requirements for on-site testing, and a need for improved seat tight-ness have lead to the development of other types of equipment to be added to thespring-loaded valve.

A variation on the spring-loaded valve is the anti-simmering device valve allowed inSection III service only. This valve employs an auxiliary actuator to hold the disc closedunder normal operating conditions, using an external source of power such as com-pressed air. The external loading is limited so that if the device fails, the valve will still

B-8



open (despite the external load) and pass its rated flow within the specified overpres-sure. When the valve is called upon to open, the assisting load is automatically removedand the valve opens. When a safe pressure is restored, the auxiliary actuator assists inclosing the valve. Due to the auxiliary load, seat tightness is enhanced up to the openingpressure of the valve. Although the ASME Code permits this anti-simmer device, it isnot generally used for a broad array of reasons (mainly equipment qualification-seeglossary for definition).

A second type of auxiliary device used on spring-loaded and pilot valves is the auxil-iary actuating device that assists the valve to open and then allows the valve to reseatnormally. When the valve is called upon to open, the assist device is actuated, openingthe PRV by mechanical means. When a safe pressure is restored, the assist device isdeactuated and the valve closes normally. If the assist device should fail to operate,there is no interference with the normal operation of the valve. (This device is typicallyused on BWR main steam safety valves.)

The second type of PRV is the pilot-operated PRV. This is a valve in which the majorrelieving device or main valve is combined with and controlled by a self-actuated auxil-iary PRV or pilot. The main valve consists of a nozzle and a disc similar to the spring-loaded valve except that the disc is held in place by system pressure. When systempressure rises above the set pressure of the valve, the pilot senses that pressure andvents the pressure above the disc allowing the main valve to open. Pilot-operated PRVshave the advantage that their operation is less influenced by fluid conditions at thevalve inlet; they generally can be tested in situ, and a high seating load is maintained upto the opening point of the valve. The valve has more operating parts, however, andbecause of typically small passages in the pilot, the cleanliness of the fluids on whichthis type of valve operates could become a concern. Pilot-operated PRVs are permittedby Sections III and VIII.

A third type of PRV is the power-actuated PRV. These valves depend upon an externalenergy source provided by electrical, pneumatic or hydraulic systems and generallyoperate in response to signals from pressure or temperature-sensing devices. This typeof PRV offers the benefits of a wide variety of control systems but has the disadvantageof relying on an external source of power that may fail under emergency conditions.Power-actuated relieving valves are often furnished on drum type boilers as a conve-nience to the operators, even though for that type of boiler Section I permits no creditfor their relieving capacity. Power-actuated PRVs are permitted by Section I and III,provided they are used in addition to self-actuated PRVs in Section I service and pro-vided that redundant controls and energy sources are included for Section III service.

B-9



4.0 Installation

The installation of PRVs is critical to their performance. It is important that they areinstalled to ASME Code requirements and each Code, ASME Section III and Section VIIIprovides specific functional and mechanical requirements to assure proper overpres-sure protection. Some of this data is covered in the following Code sections/articles:

ASME Section III

Article NB7000

Article NC7000

Article ND7000

Article NE7000

Appendix O

ASME Section VIII

Paragraph UG-125 through and including UG-136

Appendix O

ASME/ANSI B31.1

Non-Mandatory Appendix II

An additional document that provides recommendations is the American PetroleumInstitute’s document API-RP-520, Recommended Practice for the Design and Installation ofPressure Relieving Systems in Refineries.

5.0 Sizing Relief Devices

After the required relief capacity of a relief valve has been determined, in addition toother critical parameters, the minimum required orifice area must be calculated. Thiscalculation must be done in accordance with the applicable Code to which the particu-lar system is being designed and, for nuclear applications, specific subsection must beused. Example: If a safety valve for the pressurizer of a PWR nuclear plant is desired,this system, an ASME Class 1, is designed to the requirements of Subsection NB. Thespring-loaded safety valve must meet the requirements of Article NB-7000 and also therequirement for a Class 1 safety valve.

Safety valves that have been capacity certified to these requirements is published in theNBBI publication, PRD Certifications. This publication identifies valve manufacturers,valve types and styles, ASME Code section and class of certification, inlet sizes, pres-sure limit, and the certified nozzle flow area, and the certified coefficient of discharge.With this information and the ASME formula in the Article NB-7000, the valve’s capac-ity can be determined.

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It is important to note that when sizing and selecting PRVs the following must be ad-hered to:

• Use only ASME formula for the fluid being used.

• Use only ASME certified area (bore diameter).

• Use ASME certified coefficient of discharge.

• Use overpressure for which a valve was certified (do not use a 3% overpressure for amanufacturer’s valve type that was certified at 10%).

• If capacity is prorated, only use ASME formula.

For more information, ASME Section III, Appendix 18, Article 1000 and ASME SectionVIII, Appendix 11, Division 1 provide guidelines on valve capacity calculations andconversions and should be used for capacity calculations. Furthermore, for ASMESection VIII, valve manufacturers offer a variety of catalogs, technical documents, andvalve sizing programs that can be used on a personal computer to select valves for yourservice conditions. It is strongly recommend that, when in doubt and/or when ques-tions arise on valve selection, sizing, and/or capacity certification, the valve supplier orthe NBBI be contacted.

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APPENDIX CASME CODE TESTING REQUIREMENTS

1.0 Code Requirements

The requirements for nuclear safety and relief valve performance are listed in the ASMEB&VP Code Section III Article NB-7000 for Class 1 valves, NC-7000 for Class II, andND-7000 for Class III valves. Requirements are set forth for valve set pressures,blowdown, and overpressure capacity. The data summarized below is based on the1994 ASME Code Winter Addenda issued February 1995. The reader is cautioned thatthere have been changes to the ASME Code in testing requirements. It is importantthat the Code and Addenda to which the valve was manufactured (shown on thevalve nameplate and Code data report) be used for performance requirements.

Safety valve set pressure tolerances per ASME Section III, Article NB-7000 are summa-rized in Table C-1.

Table C-1Class I - Safety Valve Performance Tolerances

Set Pressure(Note 1)

0 - 70 psi 71 - 300 psi 301 - 1000psi

Over 1000psi

Manufacturer’sTolerance SetPressure

± 2 psi ± 3% ± 10 psi ± 1%

Blowdown Max.(Note 1)

95%

Overpressure forRated Capacity

Rated Capacity (Nameplate) is at 3% or 2 psi above setpressure whichever is greater

Note 1: A greater set pressure tolerance and blowdown is permitted but must be specified in thevalve design specification.

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1.1 Test Frequencies

The requirements for testing frequencies and types are set forth in the ASME B&VPCodes Section XI Sub-Section IWV-3510, ASME/ANSI Operation and Maintenance ofNuclear Power Plants Part 1 (OM-1) and the ANSI/ASME Performance Test Codes(PTC) 25.3. Prior to the winter 1985 Addenda of Section XI IWV-3510, Section XI re-quired that all safety and relief valves be tested according to the Performance Test Code25.3 (PTC-25.3).

Although PTC-25.3 (1988) is a Code for certification of PRVs, it does provide someguidelines, definitions, and requirements for calibration of instruments, training of testpersonnel, etc., PTC-25.3 also has procedures for carrying out several types of tests ondifferent process fluids, and there are sections devoted to capacity calculations forvarious test fluids.

The winter 1985 Addenda of Section XI of the ASME Code requires that safety and reliefvalves be tested to ANSI/ASME OM-1. In the 1994 edition of ASME OM-1 Code, Ap-pendix I, a mandatory appendix, is the culmination of Code work for inservice testingof pressure relief devices in light water reactor power plants.

The general requirements sections of OM-1 Appendix 1 defines the scope, terminology,and the responsibilities of plant personnel. Also included are the requirements for testingfrequency which requires all Class 1 valves of each type and manufacturer to be tested atleast once every five years. All Class 2 valves are to be tested once every ten years.

Table C-5 provides a general comparison of PTC-25.3 and Appendix 1 of the OM-1Code (1994).


1.2 Test Methods

The testing methods for determining the set pressure of PRVs regardless of fluid serviceshould incorporate the following as a minimum:

• The test media 1) for steam valves shall be saturated steam or some other compress-ible fluid for which correlating data has been developed; 2) for valves on a com-pressible fluid other than steam shall be air or nitrogen; and 3) for liquid services areliquids.

• The accumulator employed shall have a volume and pressure source sufficient todetermine valve set pressure (valve lift may be restricted).

• Assist devices may be used for set pressure testing (not allowed for liquids).

• The temperature of the valve body must be stabilized and known prior to testing.

• The ambient temperature of the operating environment shall be simulated duringtesting or a correlation factor used.

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• Control rings may be adjusted to ensure valve action. When testing for set pressure,the valve control rings cannot be altered between openings.

• Consideration for superimposed backpressure must be known and compensated forin valve set pressure (if required).

• Elapsed time between openings must be defined.(Note: At present, a 10-minute wait between openings is recommended. ASME OM-1 CodeCommittee is looking into reducing this time interval to 5 minutes. Code Case expected to bepublished in ASME OMB Code 1997.)

• As-found opening set pressure shall be within owner’s acceptance criteria.

• A minimum of two consecutive openings within owner-specified tolerance is re-quired to demonstrate valve compliance with the as-left set point of the Code.

• Blowdown testing is not required.

1.3 Test Types

There are four basic parameters associated with safety valve operation that must betested. These are set pressure, blowdown, capacity, and seat tightness or leakage. Thissection defines what is meant by each of these terms and certain methods of testing forthese variables as stated in the test method above. Inservice testing of valves, accordingto OM-1 Appendix 1, does not require blowdown or capacity testing.

1.3.1 Set Pressure

The set pressure of a PRV on steam or a compressible fluid is the pressure at which thevalve will pop. This parameter is directly affected by the amount of compressive forceexerted on the valve seat by the valve spring. The control for how much force the springexerts is accomplished by raising or lowering the adjusting bolt (Crosby) or compres-sion screw (Dresser).

One obvious way to test for set pressure is to raise the pressure of the system at the valveinlet until the valve pops. When testing for set pressure, the pressure of the system asanticipated set pressure is approached, should not be raised more than 2 psig per second.This will ensure a proper reading of the opening pressure value when the valve pops.Normally, for gas relief valves, there is a defined “pop” sound. For liquid reliefs, the setpressure can be a pencil stream, excessive flow, or even a two-step flow change.

If raising the system pressure to the valve’s set pressure is impractical, a lift assist de-vice (see Appendix D of this guide) may be used to apply the required extra force toachieve a valve opening.

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1.3.2 Blowdown

The blowdown of a valve is described as the difference between the valve’s actualpopping pressure and actual reseating pressure. The reseating pressure will be lowerthan the popping pressure. The ASME Codes place requirements on the amount ofblowdown (i.e., at what value below the popping pressure the reseating pressure canbe) that a newly manufactured valve must have. For Section III Class 1 (nuclear powerplants), it is generally required that the blowdown be specified in the valve designspecification and the basis for it be covered in the overpressure protection report.

In order to properly test for blowdown, the test facility must have adequate fluid flow tocause the valve to achieve a substantial lift and then to close. As will be explained in thenext section on capacity testing, achieving full lift on large valves like pressurizer orMSSVs can be difficult. Lift assist devices cannot be used when testing for blowdownbecause valve full lift is not achieved when lift assist devices are employed. From the twovalues (popping and reseating pressure) the blowdown can be determined as follows:

Percent Blowdown

Popping Pressure Reseating PressurePopping Pressure

x 100=−

1.3.3 Capacity

Capacity refers to the amount of fluid a valve can pass at a given overpressure in agiven time. Capacity is usually measured in gallons per minute (gpm) for water valves,pounds of steam per hour (lb/hr) for steam service, and standard cubic feet/minute(SCFM) for air.

Establishing a relieving capacity for a valve design is a complicated process, usuallyundertaken by the valve manufacturers to obtain the ASME Code symbol stamp for theparticular valve design. In order to determine the valve design capacity, the manufac-turer provides information on the valves to the NBBI. The manufacturer then, at theNBBI or any other ASME approved flow laboratory, performs certification testing.These valves undergo a vigorous testing program defined by the ASME Code to whichthe certification tests will be performed. The successful results of this testing establishescoefficient of discharge and/or other flow capacity formula constants that are used forthe valve design. This certified capacity is then stamped on the valve’s nameplate. Inaddition to the capacity test, the manufacturer must also have in place an ASME ap-proved QC program. After meeting all the Code requirements and processing the neces-sary documentation, the manufacturer receives a Certificate of Authorization from theASME that allows him to affix the ASME Code Symbol to the valve nameplate. Ifchanges are made to the valve design, another certification test must be performed.There is no requirement for a user to conduct a “capacity test” for valves that have anASME Code symbol stamp.

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1.3.4 Seat Tightness Testing

The ASME Codes, with the advent of ANSI/ASME OM-1, Mandatory Appendix I, haveestablished leakage limits for safety valves and require utilities to test PRVs for seattightness. Seat tightness requirements for newly manufactured PRVs are usuallyspecified on the valve design specification. Typically, API Standard 527, Seat TightnessPRVs, may be referenced. There are several methods mentioned in ASME OM-1 Appen-dix I that may be employed to establish whether or not a valve is leaking. For the sakeof this document, only those methods that may be used on steam service valves will benoted. The OM-1 Code requires leak tests to be performed on the valves at either maxi-mum system operating pressure or as specified by the owner. This information can beobtained from the valve design specification.

There are several methods that may be used to test for valve leakage on steam. When inservice tests are performed, these methods are either qualitative or quantitative.

• Audible/Visible Test

• Downstream Temperature Measurement Test

• Weighed Condensate Test

• Cold Bar Test

• Acoustic Emission Test

Audible/Visible Testing

When a safety valve has a major leak, the audio level of steam may be loud enough tobe heard. When steam valves are vented to the atmosphere, a visual observation can bemade against a dark background.

Downstream Temperature Measurement Testing

Steam escaping into the exhaust piping from a safety valve will raise the temperature ofthat piping. Therefore, if the temperature of the downstream piping is higher than theambient temperature, it may be concluded that the valve is leaking.

Weighed Condensate Testing

If it is possible to divert the exhaust steam flow of a valve into a container and be con-densed, then the leakage rate of a valve can be determined by weighing the amount ofcondensate in the container and dividing that by the number of hours it took to accu-mulate that condensate.

Leakage

Weight of Condensate in Pounds lbsTest Time in Hours hrs

lbs hr=( )

( )/

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Cold Bar Testing (Mirror)

Cold bar leakage testing is accomplished by passing a cold bar past the face of the valveoutlet. If the valve is leaking, steam will condense on the bar.

Acoustic Emission Testing

Acoustic emission testing is similar to audible testing except that sensitive acousticmonitors are used to pick up the acoustic (sound) emissions of the valve. By measuringhow “loud” the noises emanating from the valve are, the tester can determine the mag-nitude of valve leakage.

If in testing an alternate compressible fluid is used for set pressure testing (such as air ornitrogen), the owner may elect to use the same fluid to perform the seat leak test. In thiscase, the air/gas under water test may be used.

Air/Gas Under Water

This leakage test method allows the tester to quantify the amount of leakage instead ofjust verifying whether or not the valve is leaking. This test method is generally used onenclosed spring valve designs and is covered in API Standard 527. It is performed asfollows:

All openings that connect to the PRV outlet and body bowl are sealed. A blind flange orother sealing device is placed on the valve outlet, and a specific size tube is placedthrough the outlet flange to connect to the body bowl. If the valve seat is leaking, airwill escape through the ID of this tube which is submerged in water at exactly 1/2 inch.The leakage will escape through this tube into the water as bubbles that can be countedto give a quantitative leakage rate. The utility must set an acceptance criteria that de-fines how many bubbles are acceptable over a specific period of time. This method,although not recommended for steam service valves, may be used on pressurizer safetyvalves in addition to the steam test due to service conditions. The acceptance criteria isnot required but should be considered.

2.0 ASME OM Code Mandatory Appendix I

Appendix I of the OM Code was written strictly to provide general requirements forperiodic performance testing of PRVs used in nuclear power plants. It is not intended todemonstrate conformance to design specifications nor to verify all aspects of PRDoperation. It does establish test intervals, test methods and test data requirements aswell as criteria for evaluation. Thus, Appendix I should be thought of and used as afailure finding PM action. Like some other PM failure finding tasks, valve testing cancause aging to the valve. Testing is not a substitute for periodic valve refurbishment asdescribed in Section 8 of this guide. The following sub-sections describe the main pointsof OM-1 Appendix I and can be used as a guide for developing a valve testing program.However, the Code to which the plant has committed for the InService Testing Programshould be referred to for details.

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2.1 Seat Leakage

The first requirement for any valve test is seat tightness determinations. Seat tightnesstesting must be performed prior to as-found testing and after the final as-left set pressuretest. However, the type of seat tightness test performed is left to the utility to decidedepending upon the valve type and service conditions. Various types of seat leakage tests,their applicability and effectiveness is shown in Table C-2. The type of test performedshould be based on the importance of the individual valve to the system and the type offluid medium such as steam, air or nitrogen that it services. As an example, pressurizersafety valves typically experience system operating pressures of approximately 2300 psigwith a fluid medium of steam and non-condensable gases at saturation temperature.

Seat leakage in a pressurizer safety valve can result in seat damage. Therefore, verystringent seat tightness criteria is generally applied to these valves. However, a typicalClass III valve that usually experiences much lower pressures and temperatures mightonly require an audible/visible seat leakage test. Since Appendix I allows the utility todefine its own seat tightness criteria, the acceptance criteria should be based on eachvalve’s service environment and the consequences of valve seat leakage. The followingfactors in order of importance should be considered when selecting valve seat leakagetesting criteria:

1. The fluid medium (steam-tested with steam)

2. The effect leakage may have on the valve’s lift set point

3. Consequences of leakage on personnel safety and/or equipment damage

4. The effect on system and plant performance

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Table C-2Seat Tightness Testing Methods for Pressure Relief Devices

TEST METHOD STEAM AIR/GAS LIQUID REMARKS

Audible X X X Good for large leaks orhigh differential pressures

Visual X X X Requires open dischargepipe

ANSI 147.1 (API RP-527) X X — See note (1)

Air/gas under water X X — Requires special test setup

Downstream temperaturemeasurement

X X X Installed valves only

Weighed condensate X — — See note (1) and (3)requires a 10 min. test

Volumetric or Weightmeasurement

— — X Requires a 10 min. test

Cold bar X — — See note (2)

Acoustic emission X X X Requires specialequipment

Notes:

1. Prevent leakage past the valve stem and adjacent valve pieces for open spring valves2. Requires a 1-in.-diameter polished stainless steel bar less then 100°F be passed across

the outlet flange face.3. On exposed spring valves, care must be exercised due to leakage past stem.

2.2 Setpoint Tolerance

The set point tolerance is a requirement that specifies the pressure range the valveshould provide over and under pressure protection. Each plant’s specific as-foundrequirements may be different than what is required by the Code due to design condi-tions, but should always meet the Code requirements for the as-left condition. Thetolerances used in the set pressure testing of PRVs in accordance with the OM CodeAppendix I are determined from the individual plant’s technical specifications and thevalve’s design specification that may require compliance with Section III of the ASMECode or some other greater value. If Section III is the governing Code, it defines thesetpoint tolerances as shown in Tables C-3 and C-4.

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Table C-3Manufacturer’s Setpoint Tolerances—Safety Valves

SETPOINT TOLERANCE0 - 70 PSIG ± 2 PSIG

71 - 300 PSIG ± 3% OF SETPOINT301 - 1000 PSIG ± 10 PSIG

1001 PSIG AND ABOVE ± 1%

Table C-4Manufacturer’s Setpoint Tolerances—Safety Relief Valves and Relief Valves

SETPOINT TOLERANCE

0 - 70 PSIG ± 2 PSIG

71 PSIG AND ABOVE ± 3% PSIG

Again, it should be noted that even though Section III lists tolerances per the design ofthe PRV, they are the tolerances that the valve was designed to maintain. The valvedesign specification and the technical specifications of an individual plant may super-sede the Code specified design tolerances.

OM-1 Appendix I allows the utility to make simple set pressure adjustments if a valvefails the set pressure acceptance criteria by less than +3% of its stamped setpoint. Forany valve that exceeds its stamped setpoint by more than +3%, a root cause determina-tion must be made and the valve must be repaired or replaced.

2.3 Bellows Testing

Appendix I requires that the integrity of a bellows in a balanced valve be tested, but itdoes not specifically outline how this test should be performed. Normally, bellowstesting is carried out in the following manner:

• A blank flange or pipe cap is installed on the outlet of the valve

• Gas pressure is then applied to the outlet of the valve through a pressure connectionwelded to the blank flange or pipe cap

• The bonnet vent should be used to sense bellows leakage with soap bubble orbubble counter.

CAUTION: Any other leak path should be sealed prior to using the bonnet vent for sens-ing leakage.

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CAUTION: Pressure to be used during the bellows test should be obtained from the valvemanufacturer.

2.4 Testing Sequence

When conducting a setpoint verification test, a step-by-step procedure should be devel-oped to ensure that the test is conducted the same way each time. The procedure shouldensure that the valve’s temperature profile is the same or nearly the same as the valvewill experience in service. This is just as important when conducting in situ testing as itis for testing at a test facility. See Section 6.5 for more information about maintaining aproper valve temperature profile. OM, Appendix I gives explicit instructions as to thetypes of testing required for before and after maintenance and the sequence in whichthe testing shall be accomplished. The test scope for an individual valve depends on itsASME component class, its function in the plant and the design of the valve (Table C-4highlights some of these requirements and their sequence for valves in a Nuclear Plant).

NOTE: An OM-1 change in test sequence is expected to be approved in 1996. Whenrevised, the only required sequence of tests will be, visual inspection, as-found seat tight-ness, and as-found set pressure determination.

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Table C-5Test Requirements and Sequence

TestsPerformed

Test Sequencefor Class I

Main SteamValves with

AuxiliaryActuatingDevices

Test Sequencefor Class 1 Main

Steam Valveswithout Auxiliary

ActuatingDevices

TestSequencefor OtherClass 1

PressureRelief

Valves

TestSequencefor Class 2

and 3Pressure

ReliefValves

Visual examination 1 1 1 1

Seat tightness determination 2 2 2 2

Set pressure determination 3 3 3 3

Determination of compliancewith owners seat tightnesscriteria

4 4 4 4

Determination of electricalcharacteristics and pressureintegrity of solenoid

5 — — —

Determination of pressureintegrity and stroke capabilityof air actuator

6 — — —

Verification of the integrity ofthe balancing device onbalanced valves

— — 5 5

Determination of operationand electrical characteristicsof position indicator

7 5 6 —

Determination of operationand electrical characteristicsof bellows alarm switch

8 — — —

Determination of actuatingpressure of auxiliaryactuating device sensingelement, where applicable,and electrical continuity

9 — — —

Note: The numbers in the table show the sequence in which the tests are to be performed.

2.5 Testing Frequencies

The frequency and scope of required testing should be based on the history of pastvalve testing results but within the requirements of the governing Code. Appendix Irequires that the frequency and scope are determined by the ASME Section III Codeclassification of the valves.

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For Class 1 PRVs during the first five year period:

There is no maximum limit specified for the number of valves to be tested with eachinterval.

• A minimum number of 20% of each valve group rounded to the nearest wholenumber should be tested within any 24-month period. This 20% shall consist ofvalves that have not been tested from the current 5-year cycle, if they exist.(Note: Valve Group consists of valves of the same manufacturer, type, system application,and service media.)

• The test interval for any valve will not exceed 5 years

For Class 2 and 3 relief valves during the first 10-year period:

• There is no maximum limit for the number of valves tested during any time period.

• During a single plant operating cycle, a minimum of 20% of each valve group shallbe tested within a 48-month interval. This 20% should consist of valves that have notbeen tested from the current 10-year test interval, if they exist.

• The test interval for any valve shall not exceed 10 years

The only exceptions to this rule are PWR MSSVs. They must be tested under the re-quirements for Class I PRVs.

Replacement with Pretested Valves

OM-1 Appendix I also makes provisions for utilities that wish to change out installedvalves with pretested valves or a partial compliment of the test group.

For Class 1 Valves: If the entire scope of valves is swapped out with pretested valves,then the removed valves must be tested within 12 months of removal. If a partial com-pliment is used to replace the valves removed from service, they should be tested priorto resumption of electric power generation.

For Class 2 and 3 Valves: If the entire scope of valves is swapped out with pretestedvalves, then the removed valves must be tested within 12 months of removal. If a partialcompliment issued to replace some of the valves, then the removed valves must betested within 3 months of removal.

For Class 2 and 3 Primary Containment Vacuum Relief Valves: These valves shall be leaktested every two years, unless historical data indicates a need for more frequent testing.An operability test shall be performed every 6 months, unless historical data indicates aneed for more frequent testing.

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2.6 Requirements for Testing Additional Valves

OM Appendix I allows the utility to evaluate the need for additional tests if the valvedoes not meet certain test criteria:

For each valve tested for which the as-found set pressure (first actuation) exceeds the greater ofeither the ± tolerance limit of the owner’s established set pressure acceptance criteria or ±3% ofthe valve nameplate set pressure (not necessarily the conservative value):

• Two additional valves shall be tested of the same valve group

• If the as-found set pressure of any of the additional valves tested in accordancewith paragraph 1 above exceeds the criteria noted therein, then all of the remain-ing valves in the same valve group shall be tested.

2.7 Test Media

OM Appendix I, just as the ASME Codes to which the valves were manufactured, isvery specific about the fluid media to be used for setpoint testing. Valves designed tooperate on steam must be tested with saturated steam. Valves designed to operate onliquid and compressible fluids other than steam must be tested with their normal ser-vice fluid. OM Appendix I also requires normal service temperature and/or a correctionfactor.

Alternative fluids may be used if the correlation data between the alternative fluid andthe actual system fluid has been established. No major manufacturer contacted wouldsupply compensation charts for testing primary system safety related valves with alter-native fluids, such as testing steam valves on air or nitrogen. Since correction factors forthe use of an alternative fluid is not available, a utility desiring to use alternative fluidsmust perform tests and document the correlation. These tests should be conducted at anapproved test facility that can fully document the testing. Additional testing and corre-lation may be necessary after a rebuild or replacement of parts. Testing of this nature isbeyond the scope of this guide.

The valve users should be cautioned that if these types of correction factors are to bedetermined, a detailed review of the expected in service PRV set pressure toleranceshould be done. The tighter the tolerance, the more difficult it is to achieve a usablecorrection factor.

2.8 Testing at Inservice Ambient Temperature

During the performance of a bench or in situ test, OM Appendix I requires that theambient in-service temperature of a valve, while installed in its operating environment,must be simulated or maintained during setpoint testing. OM Appendix I also requiresthat a valve be thermally stable prior to testing with no more than a 10˚F fluctuation in30 minutes.

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2.9 ALDs

Section 4.1.2.3 of OM-1, 1981, allows the use of calibrated ALDs for set pressure deter-mination. The set pressure measurement derived from the device must meet the sameaccuracy as discussed in Section 2.11 below. However, Appendix I strictly prohibits theuse of auxiliary lift devices on liquid service valves. See Appendix D of this guide for adetailed discussion of auxiliary lift devices.

2.10 Personnel Requirements

OM Appendix I states that it is the responsibility of each individual and organizationperforming work covered by OM Appendix I to meet the requirements defined therein(See Section 9 of this guide for a detailed discussion of personnel training requirements.)

2.11 Test Instrument Requirements

OM Appendix I states that each instrument shall be of sufficient accuracy to performthe measurement task. Measuring equipment used during testing must be calibratedand traceable to National Institute of Standards and Technology (NIST). The combinedoverall accuracy of equipment used to determine the set pressure of a valve must have acombined accuracy not to exceed ±1% of the indicated (measured) set pressure.

3.0 Documentation, Records and Record Keeping

OM Appendix I gives specific requirements for records and record keeping. Detailedmaintenance records are a valuable source of information for troubleshooting valveproblems. The disassembly, inspection, and refurbishment process should be docu-mented for future reference.

3.1 Records and Record Keeping

When repair of the PRV is performed to a NR/VR program, documentation of therepair of NV stamped pressure relief devices must be recorded on the National Boardform NVR-1, Report of Repair, Modification or Replacement of Nuclear Pressure Relief De-vices. The repair organization shall file the original form with the National Board andprovide a signed copy to the owner, the jurisdiction and the authorized inspectionagency. For repairs not performed under an NBBI NR/R program, the utility will getreports per their specification and purchase order requirements.

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When repairs are performed to OM Appendix I, the following minimum requirementsare defined:

• The owner shall maintain a record that includes the following for each valve coveredby this appendix:

— The manufacturer and manufacturer’s model and serial number, or other identifiers

— Copy or summary of the manufacturer’s acceptance test report, if available

• The owner shall also maintain records that include the following information:

— Valves to be examined during each operation time period

— Procedures used in valve repair, testing, and maintenance

— Results of valve examinations

— Descriptions of repairs and modifications or corrective actions

— Valve test schedules

— Types and results of tests

— Analysis of tests which do not satisfy acceptance criteria, or evaluation of testanomalies

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Table C-6SECTION XI / PTC 25.3 AND OM CODE—General Comparison Chart

Section XI/ASME ANSI-PTC 25.3

Requirements

ASME OM CodeRequirements

1. Prior to winter, 1985. Section XI requiredvalve testing in accordance with PTC 25.3.1976 Edition.

ASME Code Section XI, 1985 winteraddenda requires all testing in accordancewith the requirements of ASME OMStandard Part 10. Now referred to as ASMEOM Code Appendix I.

2. Tolerances used for setpoint testing aredetermined from:a) Technical specificationsb) Section III of the ASME Code.

Tolerances used for setpoint testing aredefined in the individual plants' technicalspecifications or the ASME Code asinvoked by the owner.

3. A valve failing to function properly duringtest shall be repaired or replaced.

If a PRV fails to meet the set pressurecriteria:a) Simple set pressure adjustments may bemade if the valve fails the set pressurecriteria based on before maintenance testrequirements.b) If the valve exceeds its stampedsetpoint, a root cause determination mustbe made and the valve must be repaired orreplaced.

4. Liquid service valves shall be tested with aliquid and compressible fluid valves shall betested with a compressible fluid.

a) Valves designed to operate on steammust be tested with saturated steamb) Valves designed to operate on liquid andcompressible fluids other than steam mustbe tested with their normal service fluid atits normal service temperature.

5. Compensation for differences in test mediatemperature and operating mediatemperature is required.

a) Ambient temperature of a valve, whileinstalled in its operation environment, mustbe simulated during setpoint testing.b) The valve to be tested must be thermallystable prior to testing, with no more than a10°F fluctuation in thirty minutes.

6. Safety and relief valve setpoints shall beverified in accordance with the technicalspecifications and the current in-serviceinspection programs.

Safety and relief valve setpoints shall beverified in accordance with the technicalspecifications and the current in-serviceinspection programs and at a frequencyspecified in OM-1.

7. After the initial test schedule has beencompleted, all PRVs that have not beentested during the previous five years mustbe tested during the next refueling outage.

See Item #6 above.

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Table C-6SECTION XI / PTC 25.3 AND OM CODE—General Comparison Chart (cont.)


Requirements


8. If any valve in a system fails to meetacceptance criteria, additional valves shallbe tested as determined by:

N+12 X T, 60

Where, N=No. of months since previoustest cycle. T=Total number of valves in testprogram.

This requirement is based on similar valvesin a system (i.e., may not be same type ormanufacture).

The utility may evaluate the need foradditional testing if the valve does notexceed as found set point (see Section2.5). This requirement is based on similargroup of valves.

9. If any valve within the expanded scope failsto meet the acceptance criteria, the all ofthe PRV within that system must be tested.

See Section 2.5, Appendix C of this guide.

10. A test supervisor shall be responsible forcarrying out all tests.

Owner establishes his program andqualifications.

11. The test supervisor must meet the followingqualifications:1. A formal education in thermodynamicsand fluid mechanics.2. Two years experience in fluid flowmechanics.3. Prior experience in test supervision.

See Item #10 above.

12. For final results, other than flowmeasurements, the measurementuncertainty is not expected to exceed±0.5%.

Combined instrument accuracy not toexceed ±1%. (See Section 2.11, AppendixC of this guide.)

13. The use of commercial metal-encasedthermometers is prohibited.

Not Addressed.

14. The code allows:1. Testing in situ by manipulating thesystem pressure.2. Testing in situ by an auxiliary lift device.3. Removing the valve from the system andtesting its performance on a test stand.

OM Appendix I allows:1. Bench testing.2. In situ testing with an auxiliary lift device.

15. Auxiliary lift devises must be calibrated withthe final measurement uncertainty of the liftdevice ≤2%.

See Section 2.9, Appendix C of this guide.

16. Test stands with "limited" accumulatorvolumes may only be used to test for setpressure and seat leakage.

No specific size required.

C-18



Table C-6SECTION XI / PTC 25.3 AND OM CODE—General Comparison Chart (cont.)


Requirements


17. When testing compressible fluid servicevalves, the test pressure should be raisedto 90% of the setpoint and then increased2 psi/sec until the set pressure is achieved.

Not Addressed.

18. After a PRV has been repaired, a setpressure test is required.

After a PRV has been repaired, a setpressure test and seat tightness test isrequired.

19. Test accumulator diameter should be tentimes the valve nominal inlet size whentesting compressible fluid valves and fourtimes the valve nominal inlet size whentesting liquid service valves.

No specific size requirement.

20. Seat tightness may be determined byseeing, hearing, or feeling.

Seat tightness determinations must beperformed prior to "as found" testing andafter the final "as left" set pressure test.

21. The duration of the setpoint test shall bethat required to obtain the necessaryperformance and capacity data understable conditions.

Once the first test (as found) is completed,a waiting time of 10 minutes must elapsebetween successive lifts.

D-1



APPENDIX DAUXILIARY LIFT DEVICES

1.0 Auxiliary Lift Devices

There are service applications where PRVs are welded to the system piping and there isno reasonable means to raise the system pressure to the set pressure of the valves. In theseinstallations, the only means for verifying the set pressure is the use of an auxiliary liftdevice (ALD). There are also applications where the cost of removing the valve from thesystem is excessive and/or where raising the system pressure to self-actuate the PRVswould adversely affect it or other components installed in the system. In these applica-tions, the use of an ALD is desirable.

The concept behind ALDs is simple as shown in Figure D-1. The device applies an auxil-iary lifting force in conjunction with the system pressure in order to cause a PRV to lift.

Assist devices for the in situ determination of set pressure of PRVs generally consist of ameans to apply an additional lifting load to the valve stem (spindle) with the PRVinstalled on the system and the system at a pressure below the valve set pressure (gen-erally below the valve’s normal reseat (blowdown) pressure and in the range of 80% ofthe valve’s set pressure). The assist device applies an increasing lifting load to the valvestem (counteracting the spring load) until the spring load on the valve seat is in equilib-rium with the pressure load (system pressure times effective seat area) as shown inFigure D-1. At this point, the valve opens. The valve opening may be characterized bya) an audible sound, b) a momentary drop in assist load, c) stem lift, and/or d) systemfluid release. At the instant of valve opening, the assist load and the system pressure arenoted and from these two values the perceived set pressure is determined. Assist de-vices may be operated manually, semi-automatically and/or fully automated to theextent that the perceived set pressure is calculated and all of the test variables, valve testset pressure, and valve data are recorded and printed so that a permanent record of thevalve test may be maintained.

D-2



CalibratedAssist Device

Spindle

Spring

Disc

Seat Area

Nozzle

4

3

AssistLoad

SpringLoad

PressureLoad

F = – +SpringLoad

PressureLoad

AssistLoad

where, F= Force at set pressure

Figure D-1ALD Principle of Operation

ALDs are recognized by the major regulatory codes:

• Section VII of the ASME B&PV Code

• NBBI publication NB-65.

• Appendix I of the ASME OM Code

• ASME/ANSI publication PTC-25.3


There are generally three guidelines shared by all of the codes:

• ALDs are an acceptable means for setpoint verification.

• ALDs should be used only on systems containing compressible fluids.

• Blowdown cannot be measured using an ALD.

1.1 ALDs Used in the Industry

There are different types of ALDs currently used in the industry. The following sub-sections give a brief description of typical devices available and points out the moreimportant factors that should be considered when using the ALD for PRV testing. TableD-1 is a general comparison of selected manufacturers of ALDs.

D-3



NOTE: Information on specific ALD equipment has been obtained from the vendor orsupplier of such equipment. NMAC neither endorses or recommends any specific equip-ment. All information in this section is provided for reference only.

Table D-1ALDs Used by the Industry

Requirement Crosby Dresser AVKIndustries

Furmanite

ASPD SPVD HSPD Hydroset Ultrastar Trevitest

AssistDeviceFluid

Air Yes Yes No No No Yes toCharge

Liquid No No Yes Yes -- Yes

Mean Seat Area No No No No Yes Yes

Orifice Size Yes No* Yes Yes No No

Uses Valve StemPosition

No Yes No No No ** No

Must knowSystem

Pressure

Yes Yes Yes Yes Yes Yes

* Must use manufacturer’s style and assembly number of the valve

** Uses acoustic sensor to determine valve open point

ASPD = Air Set Pressure Device

SPVD = Set Pressure Verification Device

HSPD = Hydraulic Set Pressure Device

1.2 Crosby ALD Devices

Crosby has three types of ALDs that are being used in the industry. These devices arethe older air set pressure device (ASPD), the new set pressure verification device(SPVD), and a more recently developed hydraulic set pressure device (HSPD). Twodevices, the ASPD and SPVD, use air for the assist force but are very different in theirmethod of determining the lift set pressure of the PRD as discussed later. The SPVD ismore of a system then just a mounted testing device. The newer HSPD at present isused primarily for fossil boiler safety valve applications and will not be discussed indetail in this section. The HSPD concept is the same as the ASPD but uses a hydraulicfluid instead of air.

D-4



1.2.1 Crosby ASPD

Crosby’s older ASPD (see Figure D-2) consists of a safety valve lifting device mountedon the bonnet of the safety valve (hand lifting gear assembly removed), an air operatedlifting motor (diaphragm sealed air cylinder having a known effective area), and apressure gage. The ALD applies and measures the differential force required to lift thesafety valve with the actual system pressure force acting on the area of the valve seatbelow the spring setting of the valve. This force is evaluated in terms of valve springforce to determine the valve’s set pressure.

Valve Adj. Bolt

Pressure Gage

Manifold Assembly

Pressure Regulator

Air Motor

Upper Plate

Spindle Adapter

Valve Spindle

Studs

Lower Plate

Base Plate

Valve Bonnet

Air Set Pressure Device forDetermining Valve Set Pressure with Type D or E Handlifting Lever Assembly Removed

Figure D-2Crosby Air Set Pressure Device

D-5



1.2.1.1 Crosby ASPD Operation

Air pressure is applied by means of the air pressure regulator or manual control valve tothe air inlet of the air motor. The resultant force is transmitted by the lower plate, throughthe spindle adapter, to the spindle of the valve, imposing a lifting force on the spindle andadding a lifting force in addition to the force from the pressure acting below the valve’sseat. When the total lifting force is equal to the spring load holding the valve closed, thevalve will partially open, simmer, or audibly leak. The air pressure to the air motor at thatpoint can be converted into valve differential set pressure from a chart of air motor pressureversus differential set pressure based on data that has been plotted from factory tests for aspecific valve type, air motor size, and orifice size (see Figure D-3).

∆P∆P is the differential set pressure

Air

Pre

ssur

e

Figure D-3Generic Crosby Graph for Air Set Pressure Device

1.2.1.2 Crosby ASPD Test Procedure Considerations

When preparing an in-plant test procedure for use of the Crosby ASPD, the followingconsiderations, covered in the Crosby technical instruction on the device, should beconsidered:

• The system pressure for set pressure testing should be in the range of 15-25% belowthe set pressure of the valve. System pressure in the blowdown range of the valve~4-10%, and system pressures below 25% of set pressure should be avoided.

• Air pressure to the air motor should be increased slowly by operating the pressureregulator.

• To determine when the valve starts to open requires the testing personnel to hear anaudible leaking noise or see a vapor emitted.

• Both the reading of the air pressure gage, the manifold assembly, and the system(steam) pressure must be recorded at the same time.

• Determine the differential pressure using specified Crosby graphs.

D-6



• This value of differential pressure when added to the system pressure is the safetyvalve set pressure.

• Normally, testing is repeated at least three times to average out data readings andmore accurately establish the opening pressure of the valve.

1.2.1.3 Crosby ASPD Application

The following are application requirements that must be met to use the Crosby ASPD:

• The Crosby ASPD requires a source of air pressure for actuation of the air motor andsufficient head room and space for mounting the device on top of the valve.

• With air pressure of 100 psig available, the ASPD can be used for determining theset pressure of valves with a maximum recommended pressure differential beneaththe valve as indicated below.

Air Motor Size and Part No. Orifice Differential Pressure (PSIG)

12 Sq. In. (SA-50601) F 2500G 2500H 1500J 875K 650

50 Sq. In. (SA-50529) K 2200K2 1800M, M1, M2 1350P 825Q 475R 325T 200

1.2.2 Crosby SPVD Model

Crosby’s latest style ALD, the SPVD, consists of two different types of head assembliesas shown in Figure D-4. A microprocessor, a signal conditioner, an integral printer, aCRT for review of test data, and a keyboard to provide operator interface are includedin a portable module. The ALD applies a force by air pressure and measures the valvestem position. Valve stem movement determines when the safety valve starts to lift. Theforce applied by the air pressure acts along with the actual system pressure under of thevalve seat. This force is evaluated in terms of valve spring force to determine the valve’sset pressure by the microprocessor. Special features of this model are:

• Valve stem position measured by a linear variable differential transformer.

• Uses a load cell to measure applied force.

• Can be supplied with either a bellows head or diaphragm head.

• Can be permanently mounted.

D-7



• Human elements, such as visual reading, manual data recording, and calculatingtest results are avoided.

• Testing can be done from remote location; the test device operator does not need tobe near the valve.

BELLOWS HEAD ASSEMBLY*

DIAPHRAGM HEAD ASSEMBLY

LVDT: Linear VariableDifferential Transformersupplies rapid and accuratevalve stem position to themicrocontroller.

Load Cell: High resolution loadcell provides continuous forcedata to the microcontroller todetermine valve set pressure.

Overtravel stop preventsSPVD from achieving full lift.

Bellows provide auxiliarylift upon pressurization.

Vent hole precludes possiblecondensation buildup andprovides additional venting.

SPVD may be adapted to anymanufacturer's springoperated valves. Solenoid Valve: Fail safe

solenoid valve controlsbellows pressurization and issequenced by the microcontrollerto exhaust bellows chamber atend of the test.

LVDT

Tension Stud

Load Cell

Load Plate(Movable)

SolenoidValve

Pressure Relief ValveSet Pressure Adjustment

SPVD may be adapted toany manufacturer's springoperated valves.

• In stainless steel, it is suitable for fixedinstallation on pressurizer valves and BWRdual function valves.

• In aluminum, its low weight and easyassembly facilitate portability for temporaryinstallation on PWR steam relief valves.

• For system interface connections of theDiaphragm Head Assembly contact thefactory.

*Accommodates fixed installation on PWRpressurizer valves and BWR dual functionvalves as well as portable installation on PWRmain steam safety relief valves.

FlexibleDiaphragm

Figure D-4Crosby Set Pressure Verification Device (SPVD)

D-8



1.2.3 Dresser Hydroset ALD

The Dresser Company’s Hydroset ALD (see Figure D-5) consists of a safety valve liftingdevice mounted on the bonnet of the safety valve (hand lifting gear assembly removed),a hydraulic operated lift assist unit, a hydraulic pump, and a pressure gage. TheHydroset applies and measures the hydraulic pressure to lift the safety valve with theactual system pressure acting under of the valve seat. This hydraulic pressure is evalu-ated by the operator to determine the set pressure of the valve.

List assist unit

Turnbuckle

Yoke

6 in. min.

Gage

Pump

13-1/2 in.

Figure D-5Dresser Hydroset

1.2.3.1 Dresser Hydroset Operation

Hydraulic pressure is applied by means of a hand pump to the Hydroset unit. Theresulting force is transmitted through the turnbuckle to the spindle of the valve, impos-ing a lifting force on the spindle along with the force of the pressure acting below thevalve. When the total lifting force is equal to the spring load holding the valve closed,the valve will partially open, simmer, or audibly leak. The hydraulic pressure indicatedby the pressure gage is recorded by the test personnel at the lift point. The Hydrosetpressure and system pressure are used to determine the valve’s set pressure.

D-9



1.2.3.2 Dresser Test Procedure Considerations

When preparing an in-plant test procedure for the use of the Dresser device, the follow-ing considerations, covered in the Dresser technical instructions on the device, shouldbe taken into account:

• The system pressure for set pressure testing should be in the range of 15-25% belowthe set pressure of the valve.

• Hydraulic pressure to the Hydroset should be increased slowly by operating thehand pump.

• To determine when the valve starts to open requires the testing personnel to hear anaudible leaking noise or see a vapor emitted.

• Both the reading of the hydraulic pressure gage and the system (steam) pressuremust be recorded at the same time.

• The Hydroset pressure as measured by the test gage must be adjusted by using thecorrection chart and for the test gage head if required.

• The corrected value of Hydroset pressure when added to the system pressure is thesafety valve set pressure.

• The Hydroset unit must be vented and purged before using; any time the system’sconnections have been opened, and once per hour during use.

• Normally, the testing is repeated at least three times to average data readings and tomore accurately establish the opening pressure of the valve.

1.2.3.3 Dresser Hydroset Application

The following are application requirements that must be met to use the DresserHydroset:

• The Hydroset device requires a hand pump for pressure actuation of the unit andsufficient head room and space for mounting the device on top of the valve.

• The corrected Hydroset test gage pressure must be corrected by the valve constantas determined by the valves orifice size.

1.2.4 Trevitest Furmanite ALD

The Trevitest ALD is designed to measure the set pressure of PSVs and to indicate thereseating pressure. The mounting device has a frame, hydraulic rams, and a load cell. Atotally enclosed power pack provides the fluid used by the rams. The electronics con-sists of a proprietary two-channel analog recorder attached to the load cell with appro-priate connections and leads. Figure D-6 shows the basic head assembly the device uses.

D-10



1.2.4.1 Trevitest ALD Operation

The Trevitest uses a hydraulic force to overcome the closing force of the valve spring.The applied force is measured by the load cell. A controlled release of the applied hy-draulic force enables the reseating point to be established. The force required to lift thevalve is provided by the hydraulic unit. The force measured by the load cell is dis-played on the recorder chart. The chart graph reads in percent of the load cell used. Forexample, 50% of a 5000 lb cell would be 2500 lbs. The 2500 lb force is reduced by theweight of the active part of the device, which is 3 lbs without the reclosing ram. Thisnumber, 2497 lbs is divided by the mean seat area. The set pressure is determined byadding the system pressure to pressure defined by the load force divided by the meanseat area. The equation is as follows:

PF W P

MSAsLC L=

− +

where,

P set pressure

P force from load cell

W weight differential of r ram

MSA mean seat area

P system pressure

s

L

LC

==

===

eclosing

To determine the Mean Seat Diameter (MSD) (refer to Figure D-7),

MSD

ID OD=

+2

where,

ID the inside seat diameter

OD the outside diameter

==

To determine the Mean Seat Area (MSA),

MSA

MSD= ( )π 2

4

D-11



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D-12



Mean SeatDiameter

ORIFICE

(Required for Trevitest)

Figure D-7Mean Seat Diameter

1.2.4.2 Trevitest Test Procedure Considerations

The following considerations should be taken into account when drafting a test proce-dure using the Trevitest:

• Only Trevitest personnel operate this equipment (this device is not sold for utilitypersonnel use).

• Accurate set pressure results can only be obtained if the valve’s MSA is preciselyknown and verification has been performed.

• The system pressure acting on the seat at the time of testing must also be known.

• If lagging or removing insulation from the valve is required, a temperature correc-tion is also required.

1.2.4.3 Trevitest Application

The following are application requirements that must be met to use the Trevitest:

• The Trevitest set pressure device requires a source of air (50 to 125 psi) pressure forcharging the hydraulic power pack, and sufficient head room and space for mount-ing the device on top of the valve.

• With the power pack charged and a method to measure the system pressure estab-lished, the Trevitest can be used to determine the set pressure of a valve.

• The correct mean seat diameter must be known for calculating the MSA.

D-13



1.2.5 AVK Industries

AVK Industries of Jacksonville, FL, manufactures the Ultrastar ALD. The Ultrastar’sprimary function is to verify the set pressure of safety and safety relief valves withouthaving to remove the valve and shut down a system or unit. External force applied tothe valve spindle coupled with system pressure and a “true” effective area are acquiredand processed in “real time.” The end result is the valve set point. This is derived fromthe following equation:

P F A Ps t= +/

where,

P nameplate set pressure

F force required to overcome seating force

A effective area

P inlet pressure at time of test

s

t

====

The Ultrastar claims to have in its database effective areas for most PRV types and con-figurations. As an engineering tool, the system can calculate custom seat areas providedthe inlet (Pt) can be varied five times whereby the valve is popped twice at each interval.Force and inlet pressure are measured and brought into the microprocessor using highresolution data acquisition and precision transducers calibrated to +/- 0.1%.

An electro-hydraulic control system fully automates the testing procedure and providesfor constant ramp speed. The system software controls the feedback loop that continu-ously monitors actuator position. Once the proper valve data is entered into the valvedatabase and the user performs the necessary automatic calibration, the test screen theninstructs the user to begin the test. This is done by simply touching two function keysthe close gripper and the start test.

The user may also click on the buttons with a mouse. The custom robotic gripper armthen closes on the threaded spindle adaptor and begins applying force to the valvespindle (the operation of the PRV is never hampered during the entire test procedure).Should the valve “hang up” or leak after test, the user can instruct the system to per-form a reclose operation whereby the closed gripper fingers apply force to the top of thespindle adapter. This takes place while the system continuously monitors safe forcelevels to prevent damage to valve spindle or disc. The system hardware is universal andcan be mounted to most exposed spindle, spring-loaded PRVs.

At the moment of valve opening, an acoustic sensor mounted on the valve body triggersthe system software to trap and process the inlet and load data. It then instantly dis-plays the test results in graphic and digital format. The results can then be stored,printed or exported.

E-1



APPENDIX ETEST BENCHES AND TEST SYSTEMS

1.0 Introduction

The design and size of each utility’s test facility is determined by the scope of repair andtesting to be conducted. Considerations include pressure, temperature and servicemedia of the PRV to be tested; accuracy of test results, the test methods and, the typeand Code class of the device. The NBBI’s VR symbol stamp Administrative Rules andProcedure NB-65 includes excellent guidance for the design of test facilities using com-pressible fluids. The jurisdiction in which a facility is located determines the necessity ofobtaining and maintaining the VR symbol stamp. Some jurisdictions exclusively deferregulation of the facility to the NRC or do not have a specific requirement. However,the use of NB-65 guidelines in setting up a test bench facility is recommended. NB-65applies to the repair and testing of ASME Code Section I PRVs and can be extended toapply to ASME Code Section III, Class 1, 2, or 3 PRVs.

NB-65 provides guidance for sizing test accumulators in cubic feet versus the valveorifice area for saturated steam and air. The size of the test vessel depends on the sizeand the setpoint of the valve and whether blowdown is to be demonstrated.

This appendix provides a simple overview of testing facilities and types of test arrange-ments. As always, valve manufacturers should be contacted for specific test instruc-tions. The equipment required to test assemblies attached to valves such as actuators,solenoids, solenoid valves, etc. are not covered since this type of test equipment isvalve-manufacturer specific.

2.0 Testing Techniques

Bench testing will typically use a combination of techniques for the performance ofperiodic testing. The test bench facility should, as a minimum, be able to perform thefollowing types of tests:

• Seat tightness

• Set pressure

• Solenoid valve

• Actuator tests

Figure E-1 through Figure E-4 show typical test bench setups used to perform the abovetests on a Target Rock pilot operated PRV.

E-2



Gag

ValveAssembly

Bonnet

Inlet BlankFlange

MainStage Seat

N2 Supply 1500 PSIG

1/2 InchPressure Line

Figure E-1Seat Tightness Test Setup

E-3



N2Supply 1500 PSIG

PilotStage Inlet

Second Stage Inlet

Figure E-2Set Pressure Test Setup

E-4



Air Operator Assembly

Solenoid ValveElectrical Junction Box

Inlet

1/2 SAE Split FlangeWith 37˚ JIC Adapter

Test Fixture

Dual Solenoid Configuration Show, Setup Is Similar ForSingle Solenoid Configuration

Figure E-3Solenoid Valve Test Setup

E-5



Independent Elec Conn

Dry Filtered Air Supply 70/110 PSIG

In Line Rotameter (Use Only WhenPerforming Leak Test)

Figure E-4Actuator Test Setup

3.0 Test Benches

The test bench or fixture used for this process can be as simple as a standpipe with aflange mounted at one end with a pressure source, a pressure regulating device, and apressure gauge. Other test fixtures can be quite sophisticated with multiple flangemounting options, automatic performance of the test, and chart recorders to documentthe setpoint data. The bench type needed depends on the number and types of PRVsthat will be tested, Code requirements, and available space.

NOTE: When performing tests on a test bench, valve blowdown cannot be determined.

4.0 Test Bench Arrangement

The following are some general requirements for test benches. A typical test bench isshown in Figure E-5:

• The test bench feed valve should be of sufficient size to permit accurate controlledflow to the PRD being tested.

E-6



• The piping connecting the test vessel to the PRV should be short and sized to assurethat correct inlet pressure at the valve inlet is recorded.

• The pressure sensing lines should be connected to the test vessel away from inletand outlet openings to avoid transient flow velocity during tests that cause errone-ous inlet pressure readings.

• The test vessel should have a length-to-diameter ratio as low as practical with apressure relief valve installed to provide overpressure protection for the vessel.

• The PRD discharge (to a safe place) during testing should be considered whendesigning the testing system.

• The air (or N2) used as test fluid supply should be clean, dry, and filtered.

E-7



Isolated VDC Power Supply (125 VDC)

Flowmeter

TestGauge (0-200 PSI)

Connect to Plant AirOr N2 Supply (120 PSI)

Test Gauge

N2 Regulator

N2 Supply(Shown for Reference)

Test Fixture

Service Cabinet

Test Fixture

Figure E-5Typical Air/N2 Test Bench Arrangement

E-8



If the test bench is to be designed for testing with steam (not shown):

• Pressure supply should be capable of supplying pressure and steam at 98% quality.

• Fluid discharge from the valve should be contained, if radioactive.

• Pressure gauges should be installed to assure they are not effected by the system.

• Safety valves being tested are to be insulated to the extent required during plantoperation. The test bench must be designed with sufficient room to accommodateinstallation of insulation on the safety valve being tested.

Test bench instrumentation should be of sufficient accuracy to perform the measure-ment task. Critical measurements should be displayed on an ordinate chart or digitaldisplay. All instruments shall be calibrated to standards and traceable to the NIST. Testinstrumentation must be capable of determining valve set pressure within the limitsrequired by the Code to which it is being tested.

The following are general recommendations for test bench instrumentation:

• A recording instrument: oscillograph recorder, visual recorder or brush type re-corder with minimum chart speed of 8-inches/second to record the test events.

• A pressure transducer to monitor inlet pressure.

• Various pressure gauges that meet accuracy and range requirements to monitor testpressure for ready reference during performance of the test. This allows pressuretransducer output to be correlated with gauge pressure to permit compensation oftransducer drift.

• An LVDT or accelerometer to measure disc motion.

• A signal marker to indicate energized and deenergized solenoid assemblies.

5.0 Test System Design

This section provides general recommendations for the design of a test system usingcompressible fluids (i.e., steam or air/gas) and permits the determination of PRV setpressure and valve opening characteristics. The physical size of the required test vesseldepends on the size of the valve, its set pressure, the design of the test system, andwhether blowdown is to be demonstrated. It is beyond the scope of this section tospecify test equipment or facilities to fully evaluate the performance of some PRVdesigns that require testing at maximum allowable overpressure. For steam testing, atest line from a boiler or other source to the test system should connect to the test vesseland not directly to the safety relief valve. This will limit the amount of energy that canbe released if a valve failure occurs. This also allows the testing of PRVs at any pressureup to the boiler’s supply pressure.

Testing facilities should have the ability to thermally stabilize safety valves prior totesting. Thermal stabilization can be achieved by enclosing the bonnet/solenoid/airoperator portion of the assembly in a temperature controlled test chamber. The use of

E-9



bonnet heaters installed on the exterior surface of the bonnet to accelerate safety valveheat-up is not recommended as they can cause local hot spots and not simulate theinstalled condition of the valve. The bonnet heaters must be off during the course oftesting. Temperature sensors can be installed at specific locations on the valves beingtested. Typical safety valve thermocouple locations are shown on Figures E-6 and E-7.

If the test system medium source is of small capacity, a system configuration as shown inFigure E-8 could be used. The test medium from the pressure source, usually a compres-sor or a boiler, is supplied to a test accumulator if full flow testing is to be done. It thenflows through a pressure controlling valve into the test vessel. The pressure controllingvalve is usually a globe valve, although any throttling valve is acceptable. If the pressurecontrolling valve is of adequate size and can quickly open, large flows can be generatedincreasing the pressure above the PRV set pressure. This causes the valve to lift and besustained in its lifted condition. Figure E-9 is a simpler test system in which the test vesselis pressurized directly from the pressure source without the use of an accumulator. Flowrates through the PRV and any consequent overpressure are dependent on the flowgenerating capacity of the pressure source. However, as stated above for steam testing,source isolation is recommended due to the energy release if valve failure occurs.

If an isolation valve is installed between the PRV and the test medium it should be ofsufficient size as to not restrict the test medium source flow to the PRV. Piping betweenthe two valves should not contribute to any unnecessary pressure drops between thetest vessel and the PRV.

If the facility is designed to perform full flow testing, all valves and adapter flanges ortest nozzles must be of a design to sustain PRV discharge forces and secured to preventtransmitting the forces to the test vessel. If limited (bench type) testing is being per-formed and valve lift is to be limited during test, design the facility to sustain theseforces only.

All pressure sensing lines should be connected to the test vessel away from inlet andoutlet nozzles where transient flow velocity during testing could cause erroneous pres-sure readings. When testing with steam, any water head that develops in the gauge linemust be taken into consideration.

In the case of steam, the equipment should be insulated and steam traps or drainsshould be installed to assure a saturated steam quality of at least 98%.

E-10



Cap, Screwed

Compression Screw

Bonnet

Spring

Stem

Guide

Bellows

Body

Disc Holder

Disc

Guide Pin

Nozzle

Thermocouples

Thermocouples

Figure E-6Typical PRD Thermocouple Locations

E-11



T/C 2 Upper Bonnet

T/C 1 (Ambient)

4 to 6"

18" to 20"

T/C 3 Lower Bonnet

4 to 6"

6 to 8"

Test Drum

T/C 4 Body

Figure E-7Typical PRD Thermocouple Arrangement

E-12



TestMediumSource

Accumulator

TrapDrain

Gauges

Test Valve

Block Valveand Bypass

Control Valveand Bypass

Drain Trap

Test Vessel

Figure E-8Small Test Source

Gauges

Test Valve

Block Valveand Bypass

Control Valveand Bypass

Drain Trap

Test Vessel

TestMediumSource

Figure E-9Large Capacity Test Source

E-13



6.0 Test Vessel Sizing

It is recognized that there are practical limits to the size and maximum pressure of a testvessel used to demonstrate PRV operational characteristics. In such cases, set pressureremains the only viable test option. The recommended minimum size test vessel (15cubic feet) should be adequate for setpoint testing purposes. Appendix C to NB-65 is agood source to determine the size of the test vessel when a full flow blowdown test is tobe performed.

7.0 Typical Test Procedure

The following is a typical test procedure for verifying set pressure in a spring operatedsafety relief valve used in steam service:

Action Steps:

1. Perform a visual inspection of valve inlet and outlet flanges for any condition thatwould affect the proper mating at these areas.

2. The valve will be installed on the test bench in its normal operating position with itsnormal insulating material installed. The cap assembly will be removed and a gaginstalled to restrict the lift of the valve.

3. If the valve is large enough, a LVDT can be installed on the valve to measure the liftof the disc.

4. If size permits, thermocouples and a pressure transducer can be mounted on thevalve, and a recording instrument can be connected to all instruments to record testevents.

5. The valve should be thermally stabilized by installing a temperature chamberaround the valve and heated until thermal equilibrium is achieved. This can be doneat the test facility to achieve ambient conditions followed by additional heatup overon the test stand for inlet fluid conditions. A typical thermal equilibrium is definedin OM-1 Appendix I as when the valve body temperature does not change more than 10˚Fin 30 minutes as measured directly.

Upon achieving thermal equilibrium as defined above, hold the system at steady-state conditions for a 30 minute period. If at any time thermal equilibrium is dis-turbed, it must be reestablished and the 30 minute holding period repeated.

6. At this point, the set pressure test is ready to be performed. Raise steam pressureuntil the valve disc lifts off its seat. A total of three consecutive set pressure testsshall be performed. The safety valve set pressure must be within the prescribed setpressure and tolerance limits. If the valve requires adjustment during the tests, allinitial conditions must be reestablished and three consecutive tests performed until asatisfactory set pressure is obtained.

7. At the completion of the set pressure test, a leak check will be performed by passingthe test defined by the owner.

E-14



8. Test results can now be reviewed for accuracy and quality. The certification testreport shall include a brief summary of test events, test data, and a record of instru-mentation used with their calibration information.

F-1



APPENDIX FGLOSSARY

3.0 Terms, Abbreviations, and Symbols

Technical terms related to safety and relief devices as used in this guide are consistentwith those in Appendix I of PTC-25.3 (1988). (Note: ASME PTC-25.3 has been revised asASME PTC-25 in 1994.) Other terms specific to this document are noted with an asterisk(*). Abbreviations and symbols are defined in the beginning of this guide. Terms, abbre-viations and symbols that are commonly and unambiguously used in the industry arenot included.

3.1 Glossary of Terms

*accumulation. Pressure increase over the set pressure of a PRV usually expressed inpercentage of set pressure.

actual discharge area. Measured minimum net area that determines the flow througha valve.

aging. The deterioration of a valve caused by extended service with no preventivemaintenance.

approach channel. The passage through which the fluid must pass to reach the operat-ing parts of a PRD.

auxiliary lift device (ALD). A pneumatic, hydraulic, or mechanical device used onPRVs that applies the differential force required to lift the valve disc at a system pres-sure below the set pressure. It is used to determine the valve set pressure.

backpressure. The static pressure that exists at the outlet of a PRD due to pressure inthe discharge system.

balanced safety valve. A PRV that incorporates means to minimize the effect ofbackpressure on the operational characteristics (opening pressure, closing pressure, andrelieving capacity).

bellows. A flexible shield designed with an effective pressure area equal to the seat areaof the disc to seal it from the effects of pressure in the valve body.

blowdown. The difference between the actual popping pressure of a PRV and an actualreseating pressure expressed as a percentage of set pressure or in pressure units.

F-2



bore area. The minimum cross-sectional flow area of the nozzle.

bore diameter. The minimum diameter of the nozzle.

built-up backpressure. Pressure existing at the outlet of a PRD occasioned by the flowthrough that particular device into a discharge system.

capacity (measured relieving). The relieving capacity of a PRD measured at the flow-rating pressure, expressed in gravimetric or volumetric units.

capacity (marked or rated relieving). The portion of the measured relieving capacitypermitted by the applicable code or regulation to be used as a basis for the applicationof a PRD.

chatter. Abnormal rapid reciprocating motion of the moveable parts of a PRV in whichthe disc contacts the seat.

closing pressure. The value of decreasing inlet static pressure at which the valve discreestablishes contact with the seat or at which lift becomes zero.

cold differential set pressure or cold differential test pressure (CDTP). The inletstatic pressure at which a PRV is adjusted to open on the test stand. This test includescorrections for service conditions of backpressure and/or temperature.

compressible fluid. System or test fluid which experiences a significant change involume with a change in pressure (e.g., steam, air, nitrogen).

conventional safety relief valve. A PRV that has its spring housing vented to thedischarge side of the valve. The operational characteristics (opening pressure, closingpressure, and relieving capacity) are directly affected by changes of the backpressure onthe valve.

curtain area. The area of the cylindrical or conical discharge opening between theseating surfaces created by the lift of the disc above the seat.

*delay time (pilot-operated PRDs). The time between the opening of the pressuresensing pilot and the initial movement of the main valve disc which causes the relievingof primary pressure.

developed lift. The actual travel of the disc from a closed position to the positionreached when the valve is at flow-rating pressure.

disc. The pressure containing the moveable element of a PRV that effects closure.

*discharge channel. The passage through which the fluid must pass beyond the oper-ating parts of a PRD.

*environmental qualification (EQ). A term generally used to refer to qualification datathat demonstrates that a device will operate as required under nuclear accident condi-tions associated with loss-of-coolant accidents and other types of pipe breaks. Thesehypothesized accidents cause pressurized steam, water/chemical spray, and radiationconditions within certain plant areas. The most severe environmental conditions gener-ally occur inside primary containment structures.

F-3



*equipment qualification. A term referring to the accumulated testing experience andanalysis data, including environmental and seismic qualification data, that demon-strates that a device will operate as required under normal, abnormal, and nuclearaccident conditions. (Often confused with the term environmental qualification of EQ.)

flutter. Abnormal, rapid reciprocating motion of the moveable parts of a PRV in whichthe disc does not contact the seat.

*gag. A mechanical device installed on a safety valve to restrict or prevent valve lift orotherwise limit or prevent flow through the valve.

huddling chamber. The annular chamber pressure located beyond the valve seat forthe purpose of generating a popping characteristic.

*incompressible fluid. System or test fluid which does not experience a significantchange in volume with increasing pressure (e.g., water).

inlet size. The nominal pipe size of the inlet of a PRV unless otherwise designated.

*in situ. Safety valve testing performed with the valve installed on the system it isprotecting.

leak test pressure. The specified inlet static pressure at which a quantitative or seatleakage test is performed in accordance with a standard procedure.

lift. The actual travel of the disc away from closed position when a valve is relieving.

nozzle. A pressure containing element which constitutes the inlet flow passage andincludes the fixed portion of the seat closure.

opening pressure. The value of increasing inlet static pressure of a PRV at which thereis a measurable lift or when discharge becomes continuous as determined by seeing,feeling or hearing.

outlet size. The nominal pipe size of the outlet of a PRV unless otherwise designed.

overpressure. A pressure increase over the set pressure of a safety valve, usually ex-pressed as percentage of set pressure.

pilot valve. An auxiliary valve that actuates a major relieving device.

pilot-operated pressure relief valve. A PRV in which the major relieving device iscombined with and is controlled by a self-actuated auxiliary pressure valve.

popping pressure. The value of increasing inlet static pressure at which the disc movesin the opening direction at a faster rate as compared with corresponding movement athigher or lower pressures. It applies only to safety or safety relief valves on compress-ible fluid service.

power-actuated pressure relief valve/power-operated relief valve (PORV). A pres-sure valve in which the major relieving device is combined with and is controlled byanother device requiring an external source of energy.

F-4



pressure containing member (of a PRD) . A part which is in actual contact with thepressure media in the protected vessel.

pressure relief device (PRD). A device designed to prevent internal fluid pressurefrom rising above a predetermined maximum pressure in a pressure vessel exposed toemergency or abnormal conditions.

pressure relief valve (PRV). A PRV is a spring-loaded PRD designed to open to relieveexcess pressure and to reclose and prevent the further flow of fluid after normal condi-tions have been restored. It is characterized by a rapid opening pop action or by gradu-ally opening proportional to the increase in pressure over the opening pressure. De-pending on design, adjustment, or application, it may be used for either compressible orincompressible fluids.

pressure retaining member (of a PRD). A part that is stressed due to its function inholding one or more pressure containing members in position (also see ASME SectionIII Paragraph NX-3591).

rated relieving capacity. That portion of the measured relieving capacity permitted bythe applicable code or regulation to be used as a basis for the application of a PRD.

rated lift. The design lift at which a valve attains its rated capacity.

relief valve. A PRV actuated by inlet static pressure having a gradual lift generallyproportional to the increase in pressure over the opening pressure. It may be providedwith an enclosed spring housing suitable for closed discharge system application and isprimarily used for liquid service.

resealing pressure. The value of decreasing inlet static pressure at which no furtherleakage is detected after closing. The method of detection may be a specified water sealon the outlet or other appropriate means for the application.

reseating pressure. See closing pressure.

safety-relief valve. A PRV characterized by rapid opening or pop action, or by openingin proportion to the increase in pressure over the opening pressure, depending onapplication. May be used for liquid or compressible fluids.

safety valve. A PRV actuated by static pressure and characterized by rapid opening orpop action. It is normally used for steam and air service.

seat. The pressure containing contact between the fixed and moving portions of thepressure containing elements of a valve.

seat angle. The angle between the axis of a valve and the seating surface. A flat seatedvalve has a seat angle of 90°.

seat area. The area determined by the seat diameter.

seat diameter. The smallest diameter of contact between the fixed and moving portionsof the pressure containing elements of a valve.

F-5



seat tightness pressure. The specified inlet static pressure at which a quantitative seatleakage test is performed in accordance with a standard procedure.

set pressure. The value of increasing inlet static pressure at which a safety valve dis-plays the operational characteristics as defined under opening pressure, popping pres-sure, or start-to-leak pressure. It is one of the pressure values stamped on the safetyvalve nameplate.

setpoint. The system pressure in pounds per square inch at which the disc begins to liftoff the seat.

simmer. The audible or visible escape of fluid between the seat and disc at an inletstatic pressure below the popping pressure and at no measurable capacity. It applies tosafety or safety relief valves on compressible fluid service.

stamped set pressure. A value of pressure stamped on a PRD nameplate required bythe applicable code or regulation that specifies the set pressure of that device.

start-to-discharge pressure. See opening pressure

start-to-leak pressure. The value of increasing inlet static pressure at which the firstbubble occurs when a PRV is tested by means of air under a specified water seal on theoutlet.

stem gag. A mechanical device installed on a safety valve stem to restrict or preventvalve lift (see gag).

superimposed backpressure. The static pressure existing at the outlet of a PRD at thetime the device is required to operate resulting from pressure in the discharge systemfrom other sources.

theoretical relieving capacity. The computed capacity expressed in gravimetric orvolumetric units of a theoretically perfect nozzle having a minimum cross-sectional areaequal to the actual discharge area of a PRV or relief area of a non-reclosing PRD.

wire drawing. Erosion of the seat and disc caused by escaping steam.

valve group. Valves of the same manufacturer, type system application, and servicemedia.

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