Study on the residual stresses in girth-welded steel pipes and their evolution under internal pressure

• Effects of internal pressure on the residual stresses in girth-welded pipes were investigated.
• Internal pressure induces secondary bending moment at the girth weld.
• The bending moment significantly affect the axial and hoop residual stress evolution.

Pressurized girth-welded steel pipe is an important element in offshore and inter-field pipelines. This paper presents finite element (FE) analyses to clarify the effects of internal pressure on the residual stresses in girth-welded steel pipes. FE simulation of the girth welding process was first carried out to obtain the weld-induced residual stresses employing a sequentially coupled three-dimensional (3-D) thermo-mechanical FE formulation. Then, 3-D elastic–plastic FE analyses incorporating the residual stresses and plastic strains obtained from the preceding FE simulation were performed to investigate the residual stress behavior in the girth-welded pipes under internal pressure. The simulated results showed that when internal pressure is applied to girth-welded steel pipes, secondary bending moment is generated at the girth weld attributed to the circumferential shrinkage during the welding process, thus significantly affecting the axial and hoop residual stress evolution in the course of the mechanical loading.