Analysis of Tensile Response of an Unbonded Flexible Riser With Belt Corrosion in Tensile Armor Layers

Abstract Rupture of the outer sheath is one of the most common types of damage to unbonded flexible riser (UFR), which leads to tensile armor layers (TALs) direct contact with seawater and may induce localized corrosion in the wires. This seriously affects the safety of UFRs in service. In this article, a numerical model of UFR is developed. The errors between the tensile stiffness calculated by the model and experimental results are 7.16% and 6.75% under boundary conditions of limiting and allowing top-end axial torsion, respectively, verifying the model's correctness. The numerical model was used to study the effect of depth and length of localized belt corrosion and number of corroded wires on the tensile response of UFR, and it was found that tensile armor wire stress concentration occurred at the localized corrosion, and the relationship between localized corrosion depth and ultimate load was a third-degree polynomial; discussing the influence of belt corrosion spacing and combined corrosion interaction on the ultimate load, it was found that the combined corrosion depth and the ultimate load show a segmented linear relationship. The research on this article can provide theoretical support for the prediction of the ultimate load assessment of UFR under different corrosion conditions.