Effects of material type, preheating and weld pass number on residual stress of welded steel pipes by multi-pass TIG welding (C-Mn, SUS304, SUS316)

Abstract

A numerical procedure is provided to analyze temperature and residual stress fields in multi-pass TIG welds with different pipe and electrode material. Based on the ABAQUS software and FORTRAN codes, to appraise the temperature fields and the residual stresses over the TIG process, an uncoupled thermo-mechanical, finite element model (FEM) is developed. For considering volumetric thermal flux on the workpiece, the “GOLDACK” method is used. The silent element method is utilized to model the weld deposit. To validate the presented simulation model, the TIG process is performed in two passes on SUS304 stainless steel pipe. Then, the process is modeled for three and four passes to consider the effect of pass number on axial and hoop residual stresses in the outer and inner surfaces of the welded pipes. Additionally, the effects of base material and preheating temperature on the internal and external surface stresses of pipe are investigated. Results show that, the base material type has a greater effect on the tensile axial residual stress of the outer surface rather than that of the inner surface. However, the welding pass number shows no significant influence on the peak of the tensile axial residual stress on the inner surface of the pipe. In terms of preheating, the stress magnitude is reduced by raising the preheating temperature but with more intense in the inner surface of the pipe. Additionally, to keep the tensile axial residual stress below the base metal yield strength, the preheating at least up to 325 °C is essential.