Analysis of UOE forming process accounting for Bauschinger effect and welding

UOE forming is commonly used to manufacture offshore and onshore line pipes. The process involves multi-step plastic deformation of High Strength Low Alloy (HSLA) steel plates combined with welding along the seam. The strain path continuously changes during the manufacturing process leading to yield strength variation due to Bauschinger effect. In the present work, the Bauschinger effect in line pipe is analyzed using finite element (FE) method assuming the material to follow Chaboche combined isotropic-kinematic hardening model. The material parameters for the model were obtained from a single cycle compression-tension experiment performed using X-80 steel grade. The evolution of yield strength at select locations is estimated by extracting the strain path evolution from FE results. In general, the welding process is ignored in such studies as the changes induced are local. In the present study, the welding process is simulated to quantify its contribution. The effect of welding was found to be negligible in the overall stress distribution. However, the welding affects the ovality of the pipe, which in turn has a significant influence on the service load including buckling and collapse under external pressure.