Thermal stress analysis of spiral laser-welded tube

Laser welding of mild steel tube was carried out under the nitrogen assisting gas ambient. Finite element method (FEM) was used to predict the temperature and stress fields in a laser spirally welded tube with 1.6 mm wall thickness and 75 mm diameter. Temperature-dependent thermal and mechanical properties of steel were incorporated in the model. Laser was modeled as a 3D volumetric moving heat source. The residual stresses produced after the completion of the laser welding process were investigated. Moreover, the effect of welding speed on the level of residual stress was studied. It was found that von Mises stress attained high values in the cooling cycle after the solidification of the molten zones. The residual stress developed in the welding region was measured using the XRD technique and results were compared with the predictions. Optical microscopy and SEM were used for metallurgical examination of the welding sites. The numerically predicted residual stress was in good agreement with the XRD results. Increasing the welding speed with constant power resulted in reduction of the width of the high stress zone.