Hot Isostatic Pressing of Type 316L Powder for a Pressure Retaining Component

Hot Isostatic Pressing (HIP) has been used for many years to consolidate porosity in cast metal shapes to improve mechanical properties. When applied to fine metal powders, it becomes possible to produce Near Net Shape (NNS) items and more complex geometry components that are fully dense and offer an attractive set of properties at reduced cost. NNS items produced from powder deliver cost savings by reducing initial material usage and subsequent machining costs. Powder production and HIP processing are automated methods, which also provide protection against forging route obsolescence. Setup costs are lower and batch sizes smaller. HIPped powder microstructures are isotropic and equi-axed, with uniformly fine grain sizes not normally achieved in heavy section components, which makes ultrasonic NDE examination much easier. Inclusion contents are lower and of more benign geometry, which assists fracture assessment. Use of the technology has grown, particularly in the offshore oil industry where it is already established in high integrity applications, particularly in place of welded joints. Take-up in the more conservative nuclear industry has been slow. The quality of HIPped powder items can provide through life cost savings since there is greater assurance of structural integrity compared to welded or wrought components. In a broad program of testing, Rolls-Royce has established that HIPped powder 316L components, in items up to several tons in weight, have equivalent or slightly better strength, toughness and corrosion resistance than the forged counterpart. The Safety Case for a thin-walled pressure retaining component has been accepted and implemented.