Plasticity Induced Residual Stress in Pipes

An analytical model for predicting residual stress introduced in a pipe (away from girth weld) by plastic bending is examined. Stresses for a specific case where the pipe is bent, reverse bent and straightened are compared with results from a non-linear finite element analysis. The analytical model is then used to determine the through-thickness plasticity induced residual stress in the axial direction for a wide range of pipe geometries which are typically used offshore. It is found that the magnitude of extreme axial residual stress depends significantly on the ratio of pipe diameter to wall thickness. A simplified formula for estimating the extreme fibre tensile residual stress is derived and presented.