Numerical Simulation of Burst Failure in 2.5-Inch Unbonded Flexible Riser Pressure Armor Layers

Unbonded flexible risers have been widely used in the field of offshore engineering in recent years due to their excellent performance in extreme dynamic marine environments, structural compliance, low installation cost, and low quality. And, the internal pressure capacity of unbonded flexible risers is an important indicator of the mechanical performance of unbonded flexible risers. Based on a 2.5-inch, 8-layer typical unbonded flexible riser model, this paper examines the burst failure of the pressure armor layer. Firstly, the balance equation of each separate cylindrical layer and helical layer is derived by functional principle, and then the overall theoretical modeling of an unbonded flexible riser under axisymmetric loads is established by additionally considering the geometric relation between adjacent layers. Secondly, fully considering the complex cross-sectional geometric characteristics and the interlayer's contact with the unbonded flexible riser, a simplified numerical 7-layer model is established by Abaqus, and the material with elastic-plastic properties is conferred. Finally, the validity of the proposed theoretical and numerical methods is verified through the axisymmetric behavior of the test data. Then the burst failure of the pressure armor layer is analyzed based on the material. At an internal pressure of 42 MPa, the pressure armor layer reached its yield stress of 300 MPa, with the entire cross-section yielding between 42 MPa and 42.5 MPa. Additionally, the effect of the friction coefficient is examined.