Analysis and mitigation of the bending deformation in girth-welded slender pipes with numerical modelling and experimental measurement

Girth welded pipes are extensively used in the components of energy and chemical industries. The welding deformation modes depend on various influential factors, such as process schemes and geometric dimensions. The objective of this study is to investigate the characteristics and mechanism of the bending deformation generated in the girth welded slender pipes, and to develop mitigation schemes. Firstly, several 304-type stainless steel pipes were girth welded using four different welding schemes, and the 3D shape measuring system was employed to capture the basic welding deformation modes. Numerical models were developed to simulate the corresponding welding processes with experimental verification. And the mechanism of bending deformation was further clarified based on inherent strain theory. The results show that obvious bending was observed in the pipe of continuous full turn welding due to the non-uniform distribution of the axial residual plastic strain on the circumference. Welding of half turn tends to generate a bending from the weld starting position to the finish position besides the bending toward the weld side, which brings about the mutual elimination of the bending deformation with same direction half-turns and the superposition with reverse direction half-turns. Furthermore, a dual-torch scheme was proposed for girth welding of slender pipes and presented a great potential to mitigate the bending deformation with an improved welding efficiency.