The effect of plasticity on residual stress generation and redistribution in offshore pipelines

Abstract

The effect of plasticity induced by bending-reverse bending-straightening on residual stress generation and redistribution in pipes is examined through an analytical model, Finite Element Analysis and experimental measurements. The analytical model is based on elastic-perfectly plastic material properties, and correlates with Finite Element Analysis results, based on both elastic-perfectly plastic and Ramberg-Osgood strain-hardening material models. Comparison with experimental measurements at the pipe's crown position, furthest from the bending neutral axis, shows a similar through-thickness trend between the three methods. The proposed analytical model has enabled simplified, closed-form equations for predicting the through-thickness residual stress profile in pipes after one cycle of the bending-reverse bending-straightening process. In addition, parametric analyses using the extended analytical model with due consideration for initial residual stresses has produced practical recommendations for estimating the maximum residual stress magnitude at the pipe's crown position and around the pipe's circumference for a range of pipe sizes (outer diameter between 8in and 16in).