Impact of damaged external polymeric layer on axial compressive response of flexible pipes

Abstract

A fully three-dimensional finite element model was developed in order to study the axial compressive response of flexible pipes. The model is parameterized and features five layers, with emphasis on the layers responsible for reacting to axial loads. Tensile armor instability may occur in the form of lateral buckling and radial buckling, also known as “birdcaging”, which is influenced by several parameters, including defects on the layers that are supposed to restrain and protect the tensile armor, more specifically, the external polymeric layer. By being the outermost layer, the external sheath is responsible for keeping the pipe watertight and it is the most likely to sustain damage from launching, collision from vessels, anchors or ice structures and even damage caused by sea creatures. This article focuses on the effect of damage on the external polymeric layer on the tensile armor instability failure modes and uses a finite element model to simulate that phenomenon. For that purpose, the outermost layer was deliberately damaged with cuts on a key position. The cut dimension is parameterized for this analysis and the results will show that, if the flexible pipe is equipped with a high strength layer and the differential pressure is not taken into account, the external polymeric layer will not play an effective part on protecting the tensile armor layers from instability. However, it may influence the triggering of the instability on a specific position of the pipe.