Effect of UOE Forming Process on the Buckling Strains of Steel Pipes

Oil and gas pipelines are commonly made of steel pipes manufactured through the UOE process. This process starts with a flat steel plate, bends it into a U shape, then bends it further to form an O shape, welds the seam, and then radially expands (E) the pipe. The process induces significant residual stresses in the pipe wall. Such stresses have conventionally been ignored in past finite element analyses aimed at quantifying buckling strain thresholds. The present study develops a numerical technique to investigate the effect of the residual stresses induced in the UOE process on the local buckling strains of pipes. Two types of nonlinear 3D FEA models are developed to quantify the buckling strains of pipes under imposed bending deformation. The first model starts with a flat plate, models the UOE process to capture the residual stresses, and then subjects the pipes to imposed bending deformation, the second model assumes the pipe is free from residual stresses. Comparisons are then performed between the buckling strains predicted by both models.