Effect of asymmetric boundary conditions on flexible pipes crushing

Abstract

During installation, the tensioners of the pipe laying support vessels may impose asymmetric stress states on the inner carcass and the pressure armor of flexible pipes. Moreover, the possibility of admitting residual deformations in the cross section of flexible pipes after their installation is fundamental to allow the use of these structures in ultra-deep waters. However, these deformations are often not explicitly considered in predicting the collapse strength of these structures since the common practice is to consider symmetric stress states and collapse models with elliptical cross sections. This article thus presents a finite element approach that addresses the effect of asymmetric boundary conditions on the ovality of flexible pipes due to crushing loads. Their impact on the residual ovality in these structures after passing through the tensioners and the effect of these conditions on the wet collapse strength are also evaluated. By relying on the results from several numerical simulations, design strategies to address the asymmetric boundary conditions are discussed and a new methodology to measure ovality is proposed.