Bent Collapse of an Unbonded Rough Bore Flexible Pipe

Abstract

This paper investigates the collapse behaviour of an unbonded rough bore flexible pipe as it adopts a straight and bent configuration respectively. An unbonded flexible pipe typically consists of several layers, where each layer is designed to provide a specific structural function. The collapse strength of an unbonded rough bore flexible is provided mainly by its Flexbody layer, and enhanced by the Flexlok layer through the Flexbarrier layer in between. A 3D detailed FEA model was developed to simulate the most susceptible collapse situation, where the outermost Flexshield is assumed bleached and the external hydrostatic pressure acts directly on the outer surface of the Flexbarrier layer. This is often referred to as the wet collapse. The model was calibrated against the collapse test data performed on a 6 inch ID pipe in both straight and bent configuration. The equivalent test data shows about 5.0% reduction in the collapse strength under the bent configuration. The paper proposed a practical approach for estimating the collapse pressure for a pipe bent to various bend radii. The work presented is part of an ongoing research and development project.