Numerical Simulation of Residual Stress in Arc Welds GTAW of Incoloy800 Superalloy Pipes the thermal distribution and residual stresses developed during the circumferential butt gas tungsten arc welding (GTAW) process of Incoloy 800H pipes were simulated using the finite element method. A decoupled thermo-structural model was developed in three dimensions by use of ANSYS. Goldak model was used 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 was assumed. In order to validate the thermo-structural model, both temperature and residual stress distributions within the pipes were measured using thermocouples and strain gauges, respectively. Using this model, a parameter study performed for the process variables such as the type of heat source, material plasticity behavior, welding efficiency and heat input. imulation results compared to experiments showed that the Goldak heat source model would represent more precise results than the split heat source model. increasing heat input to 36% would increase weld bead width to around 25% . mechanical simulation results showed that isotropic and kinematic hardening behavior picking would lead to better result compared with perfect elasto-plastic state. Increasing heat input to 36% would increas axial residual stress along weld center line in the inner surface of pipe to 11%. a tension-compression distribution of the axial stresses can be seen through the thickness from the inside to the outside surface of the pipe and the hoop stresses have a tensile distribution. Present split model would be able to analisyse the temperature distribution along welding and residual stress caused by butt welding of pipes in 3D scale.