Full-Scale Validation of Stress Prediction Models for Flexible Pipe Foldless End Fitting Anchoring System

Abstract

Abstract This article presents a validation analysis of analytical and numerical models that predict the stress distribution of flexible pipe tensile armor wires at the pipe body and inside the end fitting anchoring chamber when under axisymmetric loads. It validates the method and the properties of materials and interfaces obtained using standard and customized small-scale tests. Results from an analytical model and a simplified finite element model of a foldless end fitting are compared against stresses measured in the tensile armors of a full-scale flexible pipe sample submitted to internal pressure and axial tension loads. This analysis is part of an ongoing qualification program for a foldless end fitting for offshore flexible pipes that simplifies the assembly procedure by eliminating the folding process of wires and improving its performance when under dynamic loads by reducing the stress concentration factor at the end fitting anchoring entrance. The stress profile induced on the tensile armor wires inside the end fitting differs from the one found in the pipe body due to the gradual load transfer from the wires to the epoxy resin as well as a change of the armor geometry inside the anchoring chamber. The tensile armor stress is often used as a critical parameter in design methodologies for the anchoring system, where validated models predict the stress distribution along the wire as a function of pipe layers geometry, disposition of wires embedded in resin inside the anchoring chamber, material, and interface properties. These models can predict the anchoring system maximum load capacity and stress concentration factors induced in the wires at end fitting entrance.