Advanced Post Weld Treatment of a Repair Weld in an Austenitic Header

The repair or replacement of nuclear power components outwith code is a very cumbersome, costly and time consuming exercise which is responsible for long plant shut down time and corresponding loss of electricity production. The aim of the European Union sponsored project ENPOWER was to produce advanced repair techniques and procedures for application in such circumstances to improve the integrity and life of the component and eliminate the need for expensive and sometimes difficult to execute global Post Weld Heat Treatment (PWHT). This paper describes the development and validation of an Alternative Post Weld Treatment (APWT) for a repair weld in an austenitic header component consisting of a 217mm outside diameter by 202mm thick tube plate welded to a 64mm thick cylindrical header. The development of the method using finite element (FE) analysis and the predicted residual stresses before and after application of the APWT are given. Application of the method to a full size mock up of the header is described. Comparison is made between the FE predictions and Deep Hole Drilling through thickness residual stress measurements. This leads to the conclusion that the APWT method is a suitable alternative to a standard PWHT for the control of residual stress in repair welds.