ISSI2022+Simulation study on repair welding residual stress of CrMo steel high-temperature pressure pipe weldment after extended service

Abstract

Abstract Repair welding is a common method to mitigation of damaged parts including creep voids and cracks in high temperature pressure pipelines. However, new cracks may be created due to the mechanical property degradation of aging material and excessive repair welding residual stress. In order to make a scientific and reasonable life extension or replacement decision, this paper carried out a feasibility study on the repair welding of an aged CrMo steel high temperature pressure pipe weldment. Firstly, the modified Kachanov-Rabotonov creep damage constitutive equation was used to predict the creep damage distribution of the weldment served for 26 years, and the most serious damage location for scarfing is determined. Then, the simulation study of welding residual stress was carried out with focus on the influence of material performance degradation and excavation methods. The results show that the maximum creep damage of the CrMo steel pipe weldment is concentrated in the heat affected zone (HAZ) and the adjacent base metal (BM).In total, the repair welding stress simulated with the degraded mechanical properties are lower than that with the initial mechanical properties. But, the stress discontinuity at the interface between the repair welding zone and BM is more severe due to the high level mismatch of mechanical properties, which is a key risk inducing repair welding cracks.The step repair method is recommended for engineering application based on the consideration from aspects of avoidance of the stress concentration inside the weld, and weaken the stress discontinuity of the weld boundary.