The fabrication procedure changes when changing the size of the structural components. For the weldments, the change of the welding procedure leads to the change in residual stresses which consequently affects the fatigue life of the structure. The weld size and number of welding passes are important factors which have considerable impact on the values and distribution of the welding residual stresses. This technological size effect is investigated in this study by simulating the welding process for tubular joints made of S355 and S690 structural steel. Two types of joints are studied: circumferential weld and planar K-joint. While rapidly developing, coupled thermo-mechanical analysis of welding is a powerful and versatile tool for the study of the development of thermal strains and stresses cause by welding process. In this study, both multi-pass and single-pass procedures with their corresponding simulation parameters are investigated. The resulted residual stress field when superposed into applied stresses at the joint in a crack propagation analysis yield more realistic crack pass and crack propagation life estimation.