Numerical simulation of the weld residual stresses for a man-hole drainage nozzle in a steam generator:: Design comparison

The numerical welding simulation has developed very rapidly during the last few years. The problem complexity has increased from simple 2D axis-symmetric or cross-section models to full 3D models, which can describe the entire welding process more realistically - including start-stop effects. As recent research projects indicate, a quantitative assessment of the residual stresses magnitude by means of a 3D analysis is possible. Moreover, the structure integrity with respect to fatigue, fracture or Stress Corrosion Cracking (SCC) processes can be evaluated based on the welding simulation results superimposed with the operating load (or any arbitrary disturbance transient load). This makes a more accurate life time prediction of the welded components possible. Furthermore, in order to minimize the residual stresses in components, a parametric study can be performed considering important input data like heat input or bead sequencing. It would make the development of virtual welding procedures possible, which can essentially help to cut the design and operating costs. In this paper a full 3D numerical welding simulation for a man-hole drainage nozzle in a steam generator will be presented. Two design options are considered. The residual stresses are calculated by means of an uncoupled transient thermal and mechanical FE analysis using the ABAQUS code. The paper will present a robust procedure allowing reasonable predictions of the residual stresses for complex structures in industrial practice.