Residual Stress Reduction in Single Pass Welds Using Parallel Line Reheating

Abstract

Current postweld heat treatment (PWHT) methods rely mainly on static thermal sources or line heating using dispersed beams which require significant capital investment and often pose limits on weldment size. In the current study, an alternative PWHT method based on line heating is presented and analyzed. The method, which is intended to perform low temperature stress relief, employs parallel oxyacetylene torches to induce a tensile stress in the vicinity of the weld toe. Xray diffraction (XRD) measurements taken from beadonplate (BOP) welds made using ASTM A57250 showed a 37% decrease in the peak longitudinal stress after parallel line reheating was performed. A corresponding reduction in the stress gradient on the plate surface was also observed. Welding and reheating were also modeled in sysweld to assess how torch placement affected the longitudinal stress distribution and an optimum offset was identified for the 8mm plate thickness used. Analysis of the thermomechanical history in the vicinity of the weld toe indicates that a tensile stress is superposed during reheating and is concurrent with the reduction in the peak longitudinal stress.