Controlled deposition repair procedures, which can be implemented without the need for Post Weld Heat Treatment (PWHT), save time and money, and are now permitted within National Board Inspection Code and ASME codes.
TWI, in collaboration with The Edison Welding Institute (EWI) in the USA, has completed a Group Sponsored Project (GSP) to develop repair procedures for 1.25Cr-0.5Mo and 2.25Cr-1Mo steels that can be used without performing a post-weld heat treatment (PWHT).
This project produced the best results seen in achieving a high degree of grain refinement and tempering to reduce hardness. The procedures the project team developed, together with the recent changes to the NBIC code, mean that repair welding of Cr-Mo steels is now a practical time- and money-saving option for electrical utility, petrochemical, and other companies.
The majority of codes that govern the weld repair of Cr-Mo steel components in high temperature pressure vessels and pipes require PWHT of the weld repairs to temper the weldment and reduce the residual welding stresses. Such PWHTs are extremely expensive and time consuming because of the often long hold times at the stress relief temperature and the slow ramp up and ramp down rates that are necessary. In addition, for large Cr-Mo steel components such as pressure vessels and turbine rotor casings, local PWHTs are extremely difficult to perform.