Nuclear Pressure Vessel Manufacture Using the Hot Isostatic Pressing (HIP) Process

Abstract Hot Isostatic Pressing (HIPing) has been used by Rolls-Royce to successfully manufacture nuclear plant components such as valves, piping, and pump casings; the majority of these components being manufactured from stainless steels, typically 316L. There are also considered to be potentially significant benefits to be gained by manufacturing large nuclear plant pressure vessels via the HIP process, such vessels commonly being manufactured from Low Alloy Steel (LAS) materials such as ASME SA-508. The benefits would include cost and lead-time reductions, which are particularly pertinent in relation to the competiveness of the power generation market and future nuclear power plant construction. Such vessels are a major cost and are critical path items of the primary plant. Also, material quality improvements and improved inspectability are possible via the HIP process. Welding vessel sections together using Thick-Section Electron Beam Welding (TSEBW) shows significant promise in reducing welding time and the provision of high quality welds, further reducing vessel cost and lead-time. There is also the potential with the use of TSEBW, to reduce weld inspection requirements with the weld being effectively the same as the parent material, i.e. no weld filler material is used. This paper presents an overview of the pioneering work conducted and planned by Rolls-Royce to develop a method of manufacture to combine HIPing and TSEBW to produce nuclear plant pressure vessels. Staged development is covered, starting with small billet manufacture for the purposes of material testing and examination, followed by vessel demonstrators for the purposes of proving the method of manufacture and to provide justification data, e.g. examination, pressure and thermal cyclic test data. In order to provide a balanced perspective, the paper also identifies the key challenges — risks, and capability development requirements necessary to deliver this method of manufacture.