Residual Stress Prediction of Butt-Welded Joints for Thick-Walled Pipe Using Heat-Input Method

Abstract

Residual stress of a welding joint based on finite element simulation was predicted to gain popularity in the process equipment industry. As for the nuclear power industry, the weldment located in a primary coolant system should be evaluated to verify the boundary integrity. The weld residual stress is an important load for leaks before break or fatigue crack growth estimation. Heat input is a key factor to accurately simulate the weld’s residual stress. Hence, heat transfer activities of weld beads, based on the theoretical volume heat generation rate of the weld element, were simulated using finite element analysis. The traditional method of controlling heat input in finite element method simulation of the welding process is achieved by setting the temperature monitoring point. When the melting temperature is reached, the calculation for weld bead melting is terminated. However, it does not comply with the real welding process because too many assumptions are involved. Therefore, a novel heat input function to modify the temperature differences of weld beads and weld layers was proposed to predict the temperature and residual stress field. Four simulations based on the modified heat input methods and traditional approaches were performed to predict the weld residual stress field of a butt-welded joint for thick-walled pipe and were compared with experimental data. Results show that more accurate thermal fields and weld residual stress fields were achieved using the proposed heat input approach.