Behavior, failure analysis, and effectiveness of mechanical stress improvement process in residual stress relaxations in butt-welded austenitic piping using a numerical simulation approach

The mechanical stress improvement process (MSIP) is a crucial technique employed in nuclear power plants to enhance the reliability and safety of piping systems, which are susceptible to stress corrosion cracking. This study aims to address the significant challenge of preventing such failures by effectively eliminating residual tensile stresses present in weldments. By mitigating these stresses, MSIP helps prevent the formation of new cracks and slows the progression of existing ones in piping systems. This approach induces beneficial compressive stresses along the inner surface of the pipe near the weld, including the molten and heat-affected zones. Multiple cases were analyzed through numerical simulations to assess the efficacy of MSIP in reducing stress concentrations and enhancing structural integrity. Furthermore, the dimensions and placement of the MSIP tool were evaluated, revealing that the optimal position and width of the clamp are 30 mm from the weld line (WL) and 75 mm, respectively. The results indicate that the WL region experiences significantly high compressive stresses, which gradually decrease within a 10-mm distance on each side of the WL. This research contributes valuable insights into the application of MSIP in improving the durability and safety of nuclear piping systems.