Effect of cyclic load on relaxation of residual stress in butt-weld joint of nuclear reactor piping

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

Weld residual stress is one of the most important factors for stress corrosion cracking growth in nuclear reactor piping weld joints. Recently very large earthquakes which exceed the design base seismic load, such as the Niigata-ken Chuetsu-Oki Earthquake and the Great East Japan Earthquake, have occurred in Japan. In order to assess the structural integrity of piping welds under such a large earthquake, the effect of cyclic loading subjected to piping due to the large earthquake on the residual stress has been analyzed with finite element method. After conducting welding simulation, effects of crack existence, cyclic loading patterns and maximum load to piping welds on variation of weld residual stress have been evaluated. The analyses showed that higher cyclic load caused larger relaxation of weld residual stress near piping welds.