Lateral Buckling of Tensile Armor Wires in Flexible Pipe Subject to Axial Compressive and Cyclic Bending Load

Abstract

Abstract Flexible pipes and subsea cables are often manufactured with a number of helically wound armor wire layers. Lateral buckling of tensile armor wire may occur when the flexible pipe is exposed to combined axial compressive load and cyclic bending. During installation and operation in hash offshore environments, the touch down section of the flexible pipe may subjected to compressive axial load together with cyclic bending, which can lead to severe damage to the flexible pipe due to the lateral buckling failure mode. The present study investigates the lateral buckling capacity of one 8” flexible riser using Repeated Unit Cell (RUC) modelling technique. The RUC model has been proven to be valid in predicting the onset of the material yield in the most vulnerable tensile layer by comparing the results with a full-scale test data. Development of the stress components in the tensile amor wires as a function of cyclic bending, distribution of gaps between tensile armor wires around circular position are discussed. Lateral buckling is assumed to occur when the total axial stress exceeds yield stress of the armor material. Lateral buckling capacity is defined as the ability of the cross section to withstand certain amount of axial compression when it is exposed to a certain number of cyclic bending.