Numerical simulation to study the effect of tack welds and root gap on welding deformations and residual stresses of a pipe-flange joint

This paper presents a three dimensional sequentially coupled non-linear transient thermo-mechanical analysis to investigate the effect of tack weld positions and root gap on welding distortions and residual stresses in a pipe-flange joint. Single-pass MIG welding for a single 'V' butt-weld joint geometry of a 100 mm diameter pipe with compatible weld-neck ANSI flange class # 300 of low carbon steel is simulated. Two tack welds at circumferentially opposite locations, with the crucial effect of the tack weld's orientation from the weld start position is the focus in this study. Four different angular positions of tack welds (0 and 180°, 45 and 225°, 90 and 270°, 135 and 315°) are analyzed. In addition, four cases for root gaps (0.8, 1.2, 1.6, 2.0 mm) are considered and computational results are compared. A basic FE model is also validated with experimental data for temperature distribution and deformations. From the results, the axial displacement and tilt of the flange face are found to be strongly dependent on the tack weld orientation and weakly dependent on the root gap.