EPRI | Nuclear Sector Roadmaps August 2015

IN USE: POWDER METALLURGY-HOT ISOSTATIC PRESSING FOR REACTOR PRESSURE VESSEL INTERNALS AND PRESSURE RETAINING APPLICATIONS

ISSUE STATEMENT

Over the past decade, dramatic improvements in powder metallurgy-hot isostatic pressing have led to the production of very large (on order of ~2.0 meter diameter) homogenous components that are now being employed across the oil, gas, airline, and aerospace industries. Only recently has PM-HIP been recognized by ASME as an accepted manufacturing process for certain pressure retaining applications. Key issues that need to addressed to enable the introduction and wide use of PM-HIP components in pressure retaining and RPV internals applications include: 1) recognition of additional alloy specifications, assessment of crack growth and stress corrosion cracking, evaluation of irradiation embrittlement affects.

DRIVERS

Improved Inspection and Elimination of Rework/RepairLarge components produced from PM-HIP demonstrate a uniform, homogenous microstructure in all three directions. As a result, both field and shop inspection of these compo-nents is dramatically improved compared with other prod-uct forms (cast, wrought, rolled-and-welded, extruded, or forged). During manufacture, repair/rework of castings can be reduced through the use of PM-HIP.

Materials ProcurementLong lead-times (on order of 2 to 5 years for a given compo-nent) are commonly encountered for new construction or replacement due to the limited number of manufacturers available to produce components. PM-HIP offers an alter-nate supply route for new and replacement/repair applica-tions.

New Reactors (SMRs and AWLRs)Alternate manufacturing methods such as PM-HIP that allow components to be produced to near-net shape (NNS) can substantially reduce machining, fabrication, and overall production costs.

Regulatory Regulatory agencies continue to push for improved inspec-tion methods and technologies, particularly related to cast products. Due to the homogeneity of PM-HIP components, certain components would greatly benefit from being manu-factured via PM-HIP.

RESULTS IMPLEMENTATION

Materials data and information generated in support of this roadmap will be utilized to support ASME Code changes and regulatory acceptance of various PM-HIP manufactur-ing or fabrication processes. Specifically, mechanical, micro-structural, corrosion, and irradiation embrittlement data will be generated/collected to develop new Code Cases and/or to introduce specifications into the pertinent book sec-tions of the Code. Alloys used for RPV internals and for pressure retaining applications will be assessed and targeted toward ASME Boiler Pressure Vessel Code incorporation. EPRI will also work with the NRC to assure regulatory acceptance across the variety of alloys used for nuclear appli-cations. EPRI will solicit engagement by various manufac-turers to a supply/supplement materials test data to support this Roadmap.

Research results also will be implemented through the devel-opment and application of new joining or manufacturing methods. PM-HIP offers the opportunity to eliminate dis-similar metal welds, and EPRI will work directly with man-ufacturers to transfer knowledge and practices to implement the technology. Methods to reduce the overall costs of can/capsule development will also be targeted. EPRI plans to work directly with industry to develop the can/capsule tech-nology, which would allow for immediate deployment and implementation.

PROJECT PLAN

The following project plan is separated along three key tech-nological areas:

RPV Internals• Crack Growth andStress Corrosion Cracking Characteriza-

tion. Because PM-HIP represents a new product form compared to wrought, cast or forged products, regulatory agencies like the U.S. Nuclear Regulatory Commission will require additional crack growth and stress corrosion cracking (SCC) data for stainless steels and nickel-based alloys. This task will look to test multiple alloys (304L, 316L, 625, 690, 718, etc) using slow strain rate tests, crack growth tests, and various SCC tests to ascertain long-term corrosion and crack growth performance.

Materials Degradation and Aging August 2015

• Irradiation Embrittlement Assessment of Stainless Steels and Nickel-Based Alloys. Because the performance of PM-HIP alloys (304L, 316L, 625, 690, 718, etc) inside a reactor are not known, ASME/NRC currently limit the use of stain-less steels to areas where the neutron irradiation fluence levels will not exceed 1 × 1017 n/cm2 (E > 1 Mev) within the design life of the component. This task will work with DOE and universities to generate sufficient data to assess use of the PM-HIP alloys in high-fluence environments for complex components.

• Components for Small Modular and Advanced Light Water Reactors. Manufacturers have not explored the use of PM-HIP produced products for SMRs and ALWRs internals primarily due to the current limits on neutron irradiation fluence levels. Once additional testing has been per-formed, several complex components that currently require extensive fabrication and machining could be manufactured via PM-HIP. This task will work with man-ufacturers to identify and produce multiple complex pro-totype alloy components for use in SMRs and ALWRs.

Pressure Retaining Applications• Eliminate Dissimilar Metal Welds. PM-HIP can be used to

manufacture dissimilar metal (DM) components. Investi-gation and demonstration of DM joining methodologies for nozzle-to-safe-end applications will include DM plate fabrication and metallurgical and microstructural charac-terization. Once demonstrated, a full size DM nozzle-to-safe end will be produced and tested.

• Advanced Valve Manufacturing Technologies. The produc-tion of the can/capsule to retain the powder during PM-HIP fabrication makes up 25-45% of the overall cost toward valve manufacture. New methods to manufacture the can/capsule such as additive manufacturing, flex- or hydro-forming will be investigated to simplify the overall can production process. Additionally, PM-HIP will be investigated to enable reduced thickness valves.

• Hardfacing Materials Development and Application. PM-HIP hardfacing application methods and alloys have been developed and demonstrated in a laboratory environment. Transfer of this knowledge to valve manufacturers will immediately allow these new methods and alloys to be used by industry. Additional full-size component testing will also be required.

• Corrosion Resistant Coatings (CRC). PM-HIP application of coatings/claddings is one of the technologies that will be explored and demonstrated for large components (ves-sels, nozzles, piping, etc.). Methods to apply CRC have been demonstrated in other industries and will be explored for nuclear applications.

ASME Boiler and Pressure Vessel Code IssuesRecognize ASTM A988/A988M-11 and A989/A989M-11 in ASME Code. ASTM A988 covers hot isostatically pressed, powder metallurgy, “alloy steel” piping components for use in pressure systems. ASTM A989 covers hot isostati-cally pressed powder metallurgy “stainless steel” piping com-ponents for use in pressure systems. Recognition of these two specifications within ASME will enable industry to use a variety of alloys. Current alloy limits are for 316L SS (Code Case N-834) and Grade 91 (Code Case 2270). EPRI will work with ASME to incorporate the two specifications into ASME Section II-Materials.• Nickel-based Alloy Specifications (ASTM and ASME).

ASTM B834-13 covers two nickel-based alloys, Alloy 625 and 25-6HN (AL6XN). Additional nickel-based alloys including Alloys 600, 690, and 718 are alloys of interest for nuclear applications. Together with industry property data, EPRI will assemble and submit updates for the ASTM specification to cover hot isostatically pressed, powder metallurgy for nickel-based alloy pressure retain-ing applications. EPRI will then work with ASME to rec-ognize the specification.

• Recognize SA508 RPV steels in ASME Code. Recent devel-opments by EPRI/DOE have demonstrated that SA508 RPV steels can be successfully manufactured and fabri-cated. PM-HIP properties meeting or exceeding the cur-rent SA specification for forged products can be easily met. This task will focus on the development of crack growth and stress corrosion cracking data to enable accep-tance of the new product form by industry and the NRC.

RISKS

Because PM-HIP has been successfully demonstrated across several other industries for large component manufacture, development risk for the nuclear power industry has been mitigated to some degree. Areas where some risk may remain include:• ASME Boiler Pressure Vessel Code process and approval• Irradiation embrittlement• Crack growth and SCC resistance• Fabrication and properties of dissimilar joints• Need for larger HIP vessels for processing

EPRI | Nuclear Sector Roadmaps August 2015

RECORD OF REVISION

This record of revision will provide a high level summary of the major changes in the document and identify the Roadmap owner.

revision description of change

0 Original Issue: August 2014 Roadmap Owner: David Gandy

1 Revision Issued: December 2014 Roadmap Owner: David Gandy

Changes: Milestones 3, 11, and 15 completed; Moved milestone 2 to the end of 2015 and updated funding for Hardfacing Materials Development and Components for SMR and ALWR Applications.

2 Revision Issued: August 2015 Roadmap Owner: David Gandy

Changes: Updated flow chart

Materials Degradation and Aging August 2015