This paper deals with Numerical Simulation to analyse the behaviour of residual stresses in welding pipe. This work aims to develop a validation model for the simulation of phase changing after welding in multi-pass welds using a hardness test and compare the results with numerical simulation. The simulation considers the local microstructure properties changes due to the thermal welding cycles. Finally, the challenge of this work is the welding of dissimilar materials, where a calibrated model will be applied and validated to predict the effect of welding residual stresses in welding pipe. A further aim is to develop a new procedure to simulate a typical welded pipe process.