A study on the mechanical stress relieving in a butt-welded-pipe

Abstract

Heat transfer, thermal and residual stress distribution were numerically determined by using the finite element method for a butt-welded pipe. A mechanical stress relieving (MSR) treatment which was frequently used in the fabrication of pressure vessels instead of the post-weld heat treatment (PWHT) was also simulated to investigate its effect of reducing the residual stress in the welded zone by a mechanical loading. Stress redistribution in a butt-welded pipe during MSR loading was studied numerically in three different loading conditions. In this study, the inner loading case has the strongest effect on the residual stress reduction behavior among the three loading cases. The reduction quantity of the tensile residual stress near the weld centerline, when MSR treatment of the inner loading case is used after pipe welding, linearly increases when compared with the magnitude of the applied loads. When the MSR treatment is performed after pipe welding, the load case is a tensile stress if the reduction of the peak value of tensile stresses is strong. On applying a compressive MSR load to the weldment, the peak value of the compressive residual stresses are reduced quickly.