A Study of the Reproducibility and Diversity of the Supply Chain in Manufacturing Hot Isostatically Pressed Type 316L Stainless Steel Components for the Civil Nuclear Sector

Abstract

Hot isostatic pressing (HIP) of type 316 L stainless steel powder has been an established manufacturing practice for more than 25 years in the oil and gas sector and more recently in the naval defense sector. To demonstrate the capability of the powder metallurgy HIP (PM/HIP) for nuclear power applications, a systematic study of 316 L commercial powder production, encapsulation/consolidation providers, and selected HIP parameters was undertaken by the Nuclear AMRC in collaboration with the Electric Power Research Institute (EPRI). In this study, the 316 L powder specification limited the oxygen content of the powder to under 130 parts per million (ppm), which reflects the improvements that commercial powder suppliers have been making over the past decade to ensure greater powder cleanliness. The test program assessed powder supply, HIP service provider, and HIP sustain time. Excellent test results were achieved across the full range of variables studied with all billets meeting the specification requirements of ASTM A988 and additional requirements imposed based on nuclear manufacturing standards. Significantly, the study demonstrated the robustness of the PM/HIP supply chain, as material produced via differing HIP service providers resulted in very consistent material properties across the destructive test program. Furthermore, no significant difference in material properties was noted for material HIP between 2 and 8 h hold time, suggesting that the HIP process window is large. Both these results are significant from an end-user standpoint as they highlight the uniformity of the process through the full manufacturing cycle from powder procurement to destructive testing. Despite all material passing specification requirements, some property variation was noted for differing powder suppliers. Considering the systematic approach, this was attributed to powder composition, with both low oxygen and high nitrogen contents contributing to improvements in Charpy impact strength and tensile strength, respectively.