Prediction of Residual Stresses in Arc Welding of Incoloy 800H Pipes

In this investigation, the thermal and residual stresess distributions developed during the circumferential butt gas tungsten arc welding (GTAW) of Incoloy 800H pipes were simulated using the finite element method. A coupled thermostructuralmodel was developed in three dimensions using ANSYS software. A subroutine based on the Goldak model was addedto the model to simulate the distribution of arc heat source. The plastic behaviour of the material was described by Von-Mises yield function and the bilinear kinematics hardening in the mechanical part of the model, which is sequentially coupled with the thermal one. In order to validate the coupled model, temperature distributions during welding and residual stresses distributions in the welded pipes were both measured using thermocouples and hole drilling method, respectively. Using this model, a process parameter study was performed for the process variables such as welding efficiency and the amount of heat input in each pass.The results showed a tension-compression distribution of the axial stresses through thickness from inside to outside surface of the pipe and a tensile distribution for the hoop stresses. Increasing the heat input by 36% increased the axial residual stresses alongthe weld centerline on the inner surface of pipe to 11%. The present simulation model is able to predict distributions of temperature and residual stresses during the GTAW process with a reasonable precision.