The topic of this thesis is the numerical analysis of residual stresses and comparison with experimental measurement due to the welding process. Welding as a technology nowadays is one of the most common and important technologies used to join materials into an inseparable joint. Metals can be joined with metals, non-metals with non-metals, and metals with non-metals. The edge parts of the material to be welded should be prepared in advance in order to form the desired shape of the groove. Each part that is prepared for welding according to the technical documentation has a default connection that needs to be made in order for that part to be functional. As heat is used during welding, residual stresses and deformations occur after cooling the material. For the modeling of heat input during welding and the assessment of residual stresses and deformations, the finite element method, more specifically the ANSYS software, is successfully applied, whereby numerical simulation tries to replace or complement the expensive experiment. In fact, we will work to ensure that the numerical simulation and the performed experimental measurement approximately coincide. Modeling of the welding process of its connections was carried out using the classical method, the method of birth and death of elements. First of all, emphasis is placed on residual stresses. In this paper, the experimental method of measurement on the pipe connections welded by the company from Slavonski Brod Termoenergetska postrojenja TEP d.o.o. is presented first. Then, after these measurements, this paper will present the simulation of this welding and the consideration of changes in stress and deformation over time. It is important to show the importance of this influence, possible problems that may occur later when using the welded element. It is very important to demonstrate the correctness of the numerical method, which today is increasingly used and enables companies to review the situation faster and cheaper. The paper will describe the main disadvantages and advantages of numerical and experimental methods.