Testing of Safety Valves

Workshop Delta Process AcademyTesting of Safety Valves

Pressure Relief Devices

Protect Personnel and Property.

Last Line of Defence.

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Usages

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Pulp & PaperPetrochemicalPetrochemical

NuclearNuclear

RefiningRefining

Oil & Gas ProductionFossil PowerPower ChemicalChemical

AerospaceAerospace

Food & BeverageBeverageTankTank CarsSubmarine ServiceService PharmaceuticalPharmaceutical

What Is A Pressure Relief Device ?A device that opens in a state of

emergency or when in abnormal conditions.

Prevents a rise in pressure in excess of a specified value:

Blocked DischargeBlocked Discharge Thermal ExpansionThermal Expansion Exposure to External FireExposure to External Fire Failure of other Equipment such as a Failure of other Equipment such as a

Control ValveControl Valve

Can be eitherCan be either a safety valve.a safety valve. a non reclosing pressure relief device.a non reclosing pressure relief device. or a vacuum relief valve. or a vacuum relief valve.

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Must open at a predetermined pressure.(Set Pressure)

Achieve a rated relieving capacity at a specified pressure above the opening point. (Overpressure)

After a given drop in inlet pressure below the opening point, it should close and reseat tightly.

(Blow down)

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Pressure Relief Valves

DEAD-WEIGHT SAFETY VALVE

Open Discharge Pattern

Jean Disaquliers 1718

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Weight

FORCE

Balance Beam Style

7

Pressure / Vacuum Vent

(Breather Valve)

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Inlet AirInlet Air

OutletOutlet

Change Over Valve, Rupture Disc and

Purge

Pilot Operated Safety

?? ??

Pilot Op. Vs Spring Loaded ?

150# Inlet150# Inlet

116 cm116 cmw/out Leverw/out Lever

227 kg227 kg

Direct SpringDirect SpringSet 5 barg Set 5 barg

6R8 Valve6R8 Valve

64 cm64 cm111 kg111 kg

Pilot OperatedPilot OperatedSet 20 bargSet 20 barg

Control (Blowdown) RingControl (Blowdown) Ring

The Control Ring: Huddling chamber Blowdown Ring up :

Small chamber Sharp opening Long blowdown

Blowdown Ring down : Large Huddling Chamber Sluggish Opening (Simmer) Short Blowdown

Can be DANGEROUS The valve may never reach its

full flow before 10% over-pressure

F d

P

A

A’

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HuddlingHuddlingChamberChamber

Different Different disk designsdisk designs

NozzleNozzle

A = OrificeA = Orifice

Spring BonnetSpring Bonnet

BodyBody P1P1

P2P2Back

PressureBack

Pressure

A New Factor: Back Pressure

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Protected Protected SystemSystem

Superimposed Back Pressure

PRV (Closed)PRV (Closed)

DischargeDischarge Header SystemHeader System

To Flare, Recovery To Flare, Recovery System, or AtmosphereSystem, or Atmosphere

Possible Pressure SourcePossible Pressure Source



Constant Purge?Constant Purge?

BPBPSS

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Most Important Characteristics Needed for Overhaul and Testing:

Inlet Size Outlet Size MSDS + cleaning declaration Bellow Present (vent always open) Back Pressure On Site Required Back Test Pressure Max. Set Pressure (Cold Set) NB Witness / Lloyds O2 – FDA Service Type of Soft Good Materials

Test pressures in writing

Transport

Overhaul & testing

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Valve testing Procedures Conventional Spring Valve:Conventional Spring Valve:

Adjusted & Verify Set Pressure Repeatability Test Seat Tightness Test According API

527 Shell Test / Body Test Bellow Integrity

Pressure %Pressure %110110

100100

9595

9090

Where PRDs Normally Sized (Except Fire Case)

Where PRDs Normally Sized (Except Fire Case)

MAWPMAWPMAWPMAWP

AllowableAllowableOverpressureOverpressure

Typical Set PressureTypical Set Pressure

Typical OperatingPressure

(“the money maker”)

Typical OperatingPressure

(“the money maker”)

Reseat Pressure of PRV

Reseat Pressure of PRV

Blowdown % of SetBlowdown % of Set

Set Pressure Tolerance

Set Pressure Tolerance

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•SHELL TEST

External pressure source 100 PSIG

(7 BAR/G )

Valve testing Procedures

External pressure source 14.5 PSIG

(1 BAR/G )

•BELLOWS INTEGRITY

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Valve testing Procedures

Vent has to be always open!

Testing SpecsCDTP(PSIG) TOLERANCE

5 TO 70 +/- 2 PSIG

+70 TO 300 +/- 3%

+300 TO 500 +/- 2%

+500 TO 6000 +/- 1%

Tolerance On Set Pressure

OPERATING TEMPERATURE%TEMPERATURE COMPENSATION

0 TO 150ºF

-18 TO 65ºC NONE

151 TO 600ºF

66 TO 315ºC

1%

601 TO 800ºF

316 TO 426ºC

2%

801 TO 1000ºF

427 TO 537ºC

3%

Temperature adjustment

Causes of Seat Leakage

Damaged valve seating surfaces. Operating pressure to close to set pressure. Pipe strains Incorrect installation Incorrect maintenance Incorrect calibration Misapplication of materials Vibration Damaged springs Rough handling / transport / montage Manipulation of lift handle Yousing lift handle as means of transportation

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In line testing Requires accurate Requires accurate

knowledge ofknowledge of system pressuresystem pressure nozzle areanozzle area

Valve always opensValve always opens Time consumingTime consuming

HydraulicHydraulicUnitUnit

RecorderRecorderForce / LiftForce / Lift

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Safety Valve Nomenclature

MAWPMaximum Allowable Working Pressure.

The specified maximum safe “design pressure” of a vessel or system. It is often the “Set Pressure” of the safety valve.

Operating PressureThe normal working pressure in a pipe or vessel.

Set PressureThe pre determined pressure at which a safety valve starts to open and relieve.

OverpressureThe pressure over and above the set pressure required for the safety valve to fully open – expressed as a percentage.

AccumulationThe pressure rise above the MAWP (term often confused with overpressure which can be different).

BlowdownDifference between set and reseating pressure of a safety valve expressed as a percentage.


Operating Gap (or difference)Difference between the working (normal operating) pressure of the vessel or system and the set pressure of the safety valve.

Back PressureA pressure opposing the set pressure that is present in the outlet side of the safety valve. Influences valve size, style and selection.

Inlet TemperatureThe fluid temperature at the moment of relief.


Other Important Safety Valve Terms

Orifice AreaThe minimum cross sectional area of the inlet flow path (nozzle) of a safety valve. This is what is “sized”.

LiftActual travel of the disc away from the closed position when a safety valve is relieving.

SeatThe area formed between the contact of non moveable and moveable components that maintain safety valve tightness.

Questions?

Guided Tour or Documentation

[email protected] [email protected]

mailto:[email protected]




Sources Tyco Formation

Main Valve Maintenance

Model Numbering

Pilot Valves

Spring Valves Operations

Poor Performance

Safety Valve Terminologie

Test Procedures

Valve Types

Sarasin Manuel

Sapag Manuel

Crosby Manual

USA ASME I Boiler applicationsASME III Nuclear applicationsASME VIII Unfired Pressure Vessel ApplicationsANSI/ASME PTC 25.3 Safety and Relief Valves - performance test codesAPI RP 520 Sizing selection and installation of pressure relieving devices in refineries, Part 1 Design, Part 2 InstallationAPI RP 521 Guide for pressure relieving and depressurizing systemsAPI STD 526 Flanged steel pressure relief valvesAPI STD 527 Seat tightness of pressure relief valves

Europe EN ISO 4126 Safety devices for protection against excessive pressureInternational ISO 4126 Safety valves - general requirements

Belangrijkste normeringen

Business

Testing of Safety Valves