Behavior, Failure Analysis, and Effectiveness of Mechanical Stress Improvement Process in Residual Stress Relaxations in Butt-Welded Austenitic Piping Using a Numerical Simulation Approach

Abstract The utilization of the Mechanical Stress Improvement Process (MSIP) is a widely employed technique to improve the behavior and the failure analysis in nuclear power plants. Its purpose is to effectively prevent stress corrosion cracking by eliminating residual tensile stresses present in weldments. This approach serves to impede the formation of cracks and decelerate the advancement of existing failures in piping systems. Consequently, favorable compressive stresses are created along the inner surface of the pipe near the weld, including molten and heat-affected metal zones. To assess the efficacy of MSIP in reducing stress concentrations and enhancing structural integrity, multiple cases were evaluated via numerical simulations in this study. Moreover, the dimensions and placement of the MSIP tool were discussed, with the optimal position and width of the clamp being determined to be 30 mm from the weld line (WL) and 75 mm, respectively. The results of this study indicate that the WL region manifests significantly high compressive stresses, which gradually diminish within a 10 mm distance on each side of the WL.