The significance of weldment material mis-matching on stress redistribution and creep cracking of high temperature components

A large circumferentially oriented crack was discovered in a weld of a double T-piece in the main steam pipe of a Swedish power plant. The pipe and the weld were manufactured from 0.5Cr0.5Mo0.25V steel. In this paper a nominal creep life assessment and an assessment considering mis-matching are carried out for a defect free component and for a component with a crack. While the nominal prediction of a defect free component indicates a creep life of approximately 2200000 hours, a creep life of 550000 hours is obtained when mis-matching effects and enhanced axial stresses due to system loads are considered. If mis-matching is not taken into account, as opposed to if it is, the estimated incubation plus creep crack growth time is approximately 30–70% longer.