A Study of Mechanical Stress Relief (MSR) Treatment of Residual Stresses for One-Pass Submerged Arc Welding of V-Grooved Mild Steel Plate

Abstract

The heat-transfer and thermal stress distributions in one-pass submerged arc welding (SAW) were numerically determined using the finite element method (FEM) for a V-grooved rectangular steel plate in which the weld preparation was filled during welding. A two-dimensional non-linear heat-transfer analysis was performed for a transverse section of the plate. This was followed by a thermo-elasto-plastic transient thermal stress analysis, assuming plane strain to be constant for the same model section. The same stress model was used to simulate a mechanical stress relief (MSR) treatment of the plate. This has frequently been used in the fabrication of large pressure vessels instead of post-weld heat treatment (PWHT). In this way its effect in reducing the residual stress in the welded plate was investigated. MSR was simulated by enforcing a constant displacement loading in the welding direction. The solution of the thermal stress analysis showed that it was possible for the residual stress around the weld centre to be accurately estimated by accurate modelling of the dilution of the filler metal in the fused zone of the base metal. The conclusion derived from the MSR simulation was that it could quantitatively predict the effect of reducing the residual stress in the welded plate. Only limited experimental data were available. The mechanism of stress reduction was plastic straining in regions of high residual stress. The amount of stress reduction at the weld centre had a linear relationship to the magnitude of the external stress relieving load. The numerical results for the MSR simulation agreed fairly well with experimental ones obtained from the MSR test performed on a welded plate.