Analytical Study of the Relaxation of Welding Residual Stress by Excessive Loading for Austenitic Stainless Steel Piping Welds

Welding residual stress is one of the most important factors of stress corrosion cracking (SCC) for austenitic stainless steels of the pressure boundary piping in nuclear power plants. For the assessment of the integrity of piping particularly for a long-term operation, it is necessary to understand the effect of excessive loading, such as an earthquake, on the residual stress. Three-dimensional finite element analyses were performed using three-dimensional model for a 250A pipe butt weld of low-carbon stainless steel of type 316L. The welding simulation method considering the moving heat source with the double ellipsoid model was confirmed by comparing with some experimental measurements. After conducting the welding simulation and residual stress analysis, several loading patterns of bending moment and axial displacements have been applied to the model by varying amount of moment and displacement in order to study the effect of excessive loading. The analyses indicated that higher loading of bending and axial stresses caused higher relaxation on welding residual stress near piping welds. The difference in the effect of loading direction was observed for both cases. It is concluded that excessive loading to piping butt-welds has an influence on the suppression of SCC growth due to the decrease in tensile residual stress at the inner surface.