Effect of cyclic loading on the relaxation of residual stress in the butt-weld joints of nuclear reactor piping

Katsuyama, Jinya  ; Yamaguchi, Yoshihito ; Li, Y.* ; Onizawa, Kunio 

Weld residual stress is one of the most important factors in stress corrosion cracking (SCC) of nuclear reactor piping. To assess the integrity of piping, it is necessary to understand the effects of excessive cyclic loading, caused by earthquake, on residual stress. In this study, finite element analyses were performed using a model of a 250A pipe butt weld of Type 316L stainless steel. The accuracy of the welding simulation was verified by comparing the calculated results with the experimental measurements. After conducting the welding simulation and residual stress analysis, several loading patterns for the axial cyclic loadings were applied to the model by varying the amount of maximum load, in order to study the effect of excessive cyclic loading. The analysis indicated that higher loading caused a greater relaxation of the weld residual stress near the piping welds. It was thus concluded that excessive cyclic loading on piping butt welds affects the suppression of SCC growth.