The objective of this project is to analyse welding processes in high strength low-carbon steel grade S690 in numerical simulation with MORFEO codes and in experiments with a Gleeble® thermo-mechanical simulator instrument. The influence of phase transformation on residual stresses is investigated with simulations on plate to plate and on tube to plate connections. Furthermore, this study investigates the effects of element activation on numerical results and the possibilities to simplify multi-pass welding by lumped models. In addition to literature based descriptions of temperature depending steel properties, experimental tests are conducted to survey the behavior of steel grad S690 at elevated temperatures.