Stress state of unbonded flexible pipe’s tensile armour wires inside end-fittings

Abstract

The present paper addresses the stresses developing, inside the End-Fitting (EF), on the tensile armour wires of a metal based unbonded flexible pipe under axial tensile operational loads. To this end, a bi-dimensional finite element model that estimates the stress state of tensile armour wires inside the EF is developed. The stresses induced during the EF assembling procedure as well as the Factory Acceptance Test (FAT) are considered in the developed numerical model. An analytical approach to this problem, suggested by Campello (2014) and Campello et al. (2016), is utilized as a benchmarking tool in order to evaluate the developed numerical model’s performance. The results obtained show good agreement between the developed model and the analytical approach. A high concentration of stresses on the tensile armour wires inside the EF, at a key point near the EF’s entrance, is observed under all operational load cases. Moreover, the results suggest that the EF assembly procedure and the FAT test need to be indeed considered, as they yield significant residual stresses on the tensile armour wires inside the EF.