Finite element analysis of flexible pipes under compression: A study on the damaged high strength tape and its effects on tensile armor instability

Abstract

To study the compressive behavior of flexible pipes and tensile armor instability, a nonlinear Finite Element model was developed. This fully tridimensional model recreates a five layer unbonded flexible pipe. When the pipe is submitted to compressive loads, tensile armor instability may occur in the form of lateral buckling or radial buckling, also known as “birdcaging”. This complex failure mode may be influenced by several parameters, including defects on the layers that are supposed to restrain and protect the tensile armor, more specifically, the high strength tape. This layer is usually made of high a performance textile material that is not directly exposed to the environment. However, damage may be sustained when the outermost layer is subjected to deep cuts and breached. This article focuses on the effects of a damaged high strength tape and its implications on the tensile armor instability failure modes. The study shows that damage in the high strength tape may compromise the cohesion between the layers, significantly reducing the critical instability load and the flexible pipe's stiffness, as well as altering the yielding for the layers.