As nuclear plants around the world grow older there are increasing incidences of stress corrosion cracking (SCC) problems. In PWRs such cracking is well known and often associated with reactor pressure vessel parts eg primary water SCC at reactor nozzle locations.
However SCC also occurs in the secondary circuit and auxiliary parts of the plant which are also safety-critical. This repair development is aimed at relatively thin-walled Type 304 stainless steel water storage tanks which have experienced SCC cracks at the external surface.
Friction stir processing is a technique which has grown out of TWI's friction stir welding expertise and essentially provides a high integrity smooth repair of shallow surface breaking defects. For this particular application, the utility customer considered it offers advantages for on-line application particularly in terms of its controllability and lower risk of through-wall penetration when compared with conventional weld repair methods.
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