Numerical Simulation Study on Residual Stress in Repair Welding of a CrMo Steel High-Temperature Pressure Pipeline Weldment Under Extended Service

Abstract Many high-temperature pressure pipelines in thermal power plants are prone to failure due to long-term service-induced creep damage, which significantly impacts the normal operation of the equipment. Repair welding is a widely adopted method to mitigate damage, including creep voids and cracks, in high-temperature pressure pipelines. However, the mechanical property degradation of aging material and excessive residual stresses from repair welding can lead to the formation of new cracks. To support scientifically sound decisions regarding life extension or replacement, the feasibility of repair welding for an aged CrMo steel high-temperature pressure pipeline weldment is investigated in this study. Firstly, the modified Kachanov-Rabotonov creep damage constitutive model is employed to predict the creep damage distribution of the weldment that had been in service for 26 years, identifying the most severely damaged location for scarfing. Subsequently, a numerical simulation study is conducted to analyze the residual stress in repair welding, with a focus on the influence of material performance degradation and excavation methods. The results indicate that the maximum creep damage in the CrMo steel weldment is concentrated in the heat-affected zone (HAZ) and the adjacent base metal (BM). Overall, the repair welding stresses simulated with degraded mechanical properties are lower than those with the virgin mechanical properties. However, the stress discontinuity at the interface between the repair welding zone and the BM is more pronounced due to the high-level mismatch in mechanical properties, which poses a significant risk for inducing repair welding cracks. Based on the consideration of avoiding stress concentration within the weld and reducing stress discontinuity at the weld boundary, the step repair method is recommended for engineering applications.