Numerical analysis of multi-pass welding residual stress for typi-cal closed weld

Two typical closed weld, circular patch weld and noz-zle weld, were modeled and 3-D multi-pass welding simulation were performed using FEM.User subroutine were used to realized the moving Gauss distribution of welding heat source.The thermal cycle and residual stresses distribution were obtained. The results show that the maximum hoop tensile residual stress exists in the region of the start/stop point of the circular weld for above two models, where the stress distribution is complex and the larger hoop tensile stresses are always regarded as the driven force of weld fracture.As comparison, the case of the nozzle weld needs more attention.