The importance of welding process modeling is specifically related to the role of the induced welding residual stresses and distortions on the structural behavior of the components under service load. In the absence of reliable information on the magnitude and distribution of residual stresses, it is generally assumed that residual stresses are as high as the yield strength of the material that could lead to overconservatism in design and consequently economic challenges. The more exact the microstructure and residual stress or strain fields is predicted, the better one can judge the risk of structural damage, for example, the formation of fatigue cracks or initiation of failure. In this chapter, the application of finite element approach to the calculation of welding residual stresses is described through three different case studies. SYSWELD has been used for welding simulation. Residual stress measurements are carried out to determine the distribution of residual stresses in three orthogonal directions, on the surface and in the bulk of the material. The numerical results are compared directly with the measured data. The overall aim is to evaluate the use of finite element approach in the accurate calculation of residual stress states for use in the structural integrity assessments.