The Additive Manufacture (AM) of nuclear plant components, such as small bore globe valves, offers opportunities to reduce costs and improve production lead-times. Cost reductions can be achieved by reducing the amount of raw material required, reducing the amount of machining conducted, and eliminating the welding together of sub-assemblies. The need for a high skill level for special operations such as weld deposition of wear resistant materials for valve seats can also be removed. Furthermore, there is the opportunity to reduce production lead-times by simplifying the supply chain, e.g. reducing the number of parts to be sourced and eliminating special operations.However, AM is a relatively new manufacturing technology, and although now seeing greater usage in industry generally, there are very few examples of where the technology has been applied to components used in safety critical applications. Furthermore, it is not covered by the ASME Section III nuclear design code. For nuclear plant applications, it is imperative a robust safety justification is provided.This paper presents Rolls-Royce’s approach to provision of a high integrity safety justification to enable the implementation of AM small bore globe valves, up to a bore size of 2”, to nuclear plant. The material of construction is Laser Bed Powder Fusion (LPBF)&nbsp;316LN stainless steel, with a low cobalt hard facing seat – Tristelle 5183.The paper describes the structure of the safety justification, which follows the United Kingdom’s Technical Advisory Group on Structural Integrity’s (TAGSI) four-legged approach. It provides an overview of the manufacturing process, which includes a Hot Isostatic Pressing (HIP) consolidation/bonding process step, and covers the possible material defects and the inspection regime being applied.The paper provides an overview of the suite of material property testing and metallurgical examinations conducted, and majors on prototype functional and performance testing where comparisons are made with the previous forged form. Pressure testing is covered which includes ultimate pressure testing to 2,000bar, as well as: functional cyclic testing – valve opening and closing cycles, hard facing bond strength testing, dynamic loading (shock), and cyclic thermal fatigue tests.In all cases the additive manufactured small bore globe valves performed as well, and in some cases better than the forged material equivalent.

Safety Justification Strategy for the Implementation of Additive Manufacture Small-Bore Globe Valves for Nuclear Plant

Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2021/volume/85314

ASME 2021 Pressure Vessels & Piping Conference (PVP2021)

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