Residual stress analysis and fatigue of multi-pass welded tubular structures

The purpose of this study is to investigate the residual stresses near the weld root and the weld toe for multi-pass welded tube-to-plates. Two different tubular joint configurations were studied; a three-pass single-U weld groove for maximum weld penetration and a two-pass fillet (no groove) welded tube-to-plates for minimum weld penetration. A 2D axi-symmetric finite element model was developed to calculate the temperature distribution, HAZ, penetration depth and the residual stress distribution for the sequentially coupled thermo-mechanical analysis. The calculated residual stresses was compared with experimental results and showed qualitatively good agreement. Torsion fatigue tests were performed in order to study crack propagation from the weld root, lower and upper weld toe in mode III. Some of the tube structures were loaded with a static internal pressure in order to separate the root crack and initiate the crack growth in mode III. Another batch was PWHT and fatigue tested, in order to study the influence of residual stresses.