Radial Buckling of Tensile Armor Wires in Subsea Flexible Pipe—Numerical Assessment of Key Factors

Abstract

Flexible pipes can be used as risers, jumpers, and flowlines that may be subject to axial forces and outofplane bending motion due to operational and environmental loading conditions. The tensile armor wires provide axial stiffness to resist these loads. Antibirdcaging tape is used to provide circumferential support and prevent a loss of stability for the tension armor wires, in the radial direction. The antibirdcaging tape may be damaged where a condition known as “wet annulusâ€‌ occurs that may result in the radial buckling (i.e., birdcaging mechanism) of the tensile armor wires. A threedimensional continuum finite element (FE) model of a 4 in. flexible pipe is developed using abaqus/implicit software package. As a verification case, the radial buckling response is compared with similar but limited experimental work available in the public domain. The modeling procedures represent an improvement over past studies through the increased number of layers and elements to model contact interactions and failure mechanisms. A limited parameter study highlighted the importance of key factors influencing the radial buckling mechanism that includes external pressure, internal pressure, and damage, related to the percentage of wet annulus. The importance of radial contact pressure and shear stress between layers was also identified. The outcomes may be used to improve guidance in the engineering analysis and design of flexible pipelines and to support the improvement of recommended practices.