An unbonded flexible pipe typically consists of multiple metallic and thermoplastic layers, where each layer is designed to provide a specific structural function. The burst resistance against the internal pressure in an unbonded flexible pipe is provided mainly by its Flexlok layer. The Flexlok is made by helically-wound steel wires, with neighbouring wires interlocking each other. Beneath the Flexlok is the Flexbarrier, a polymer layer, acting as the boundary for conveyed fluids. The internal pressure is passed onto the Flexlok through the Flexbarrier layer. Under internal pressure, the Flexbarrier can creep into the gaps between Flexlok wires. Theoretically, the polymer material ingress could reduce the flexibility of the Flexlok due to premature lock-up between Flexlok wires and subsequently increase the stress levels. This study presents a 3D finite element analysis model developed to quantify the stress elevation in the Flexlok wire, caused by the Flexbarrier layer ingress. In terms of Flexlok gap size distribution, both nominal and worst case scenarios are studied. In the nominal scenario, the Flexlok gap sizes are evenly distributed. In the worst case scenario, the Flexlok gap is assumed to be completely closed at one position while the gaps at the neighbouring positions are twice the nominal size. Flexbarrier ingress with different temperatures is also studied. Conclusions are obtained by analyzing the simulation results. The work presented is part of an ongoing research and development project.
