Simulation and Analysis of Residual Stress and Microstructure Transformation for Post Weld Heat Treatment of a Welded Pipe

With the characteristics of the sandglass-shaped temperature field generated during welding of high-frequency induction longitudinally welded pipe taken into consideration, this paper focuses on the rules of influence of a post weld medium-frequency heat treatment process on microstructural change and the rules of residual stress distribution, and proposes a quantitative analysis method for studies on heating mechanisms of on-line heat treatment. The microstructural evolution process respect to time, and the rules of post weld axial, circumferential, radial, and residual von Mises stresses changing by path were quantitatively analyzed, respectively. It was found from comparison between a metallographic test and a microhardness test that on-line heat treatment is significantly effective in improving microstructures and reducing residual stress of the outer surface of a welded pipe. By controlling the distribution types of the microstructural field and the stress field through appropriate selection of heat treatment process parameters and distributing heat more reasonable heat distribution, it is expected that the residual stress of the inner surface of a welded pipe can be further reduced and the quality and efficiency of on-line heat treatment can be improved.