An analytical approach for assessing the collapse strength of an unbonded flexible pipe

Abstract

This paper presents an analytical scheme for predicting the collapse strength of a flexible pipe, which considers the structural interaction between relevant layers. The analytical results were compared with a FEA model and a number of test data, and showed reasonably good agreement. The theoretical analysis showed that the pressure armor layer enhanced the strength of the carcass against buckling, though the barrier weakened this effect. The collapse strength of pipe was influenced by many factors such as the inner radius of the pipe, the thickness of the layers and the mechanical properties of the materials. For example, an increase in the thickness of the barrier will increase contact pressure and in turn reduce the critical pressure.

A review on predicting critical collapse pressure of flexible risers for ultra-deep oil and gas production

“…In recent years, many equivalent methods were proposed in terms of one property of the carcass, e.g. the cross-section area, the bending stiffness or strain energy [24,[44][45][46][47]. Area equivalent method [44] was carried out based on the equivalence of cross-sectional areas.…”

“…Area equivalent method [44] was carried out based on the equivalence of cross-sectional areas. One another similar method was to use the actual thickness of the interlocked layers directly but with a fraction fill coefficient that calculated based on area equivalency [24]. As the ring thickness is simply determined by the cross-sectional area in those methods, the actual material distribution in the carcass profile is neglected.…”

“…Chen et al [24] and Bai et al [25] both considered the outside layers as a spring support to the inner carcass and thus proposed a formulation to that spring-supported ring model [24] p c = 3EI…”

“…However, the above-mentioned equations are built based on elastic collapse merely. For a flexible riser that applied to deep water environment, it is more likely to be collapsed in the plastic range [24]. Clinedinst [52] suggested that replacing Young's modulus with a "reduced modulus" to consider the plastic collapse of pipes.…”

“…Although such kind of experiments are costly, they are the foundation to develop related analytical and numerical models. Buckling theories of rings are adopted by researchers to develop the analytical models[14,24,25].Most of them are limited to simplified ring models due to the complexity of the carcass profile [23]. By contrast, numerical simulation, such as Finite Element Analysis (FEA), has less limitations in modeling the carcass with its actual profile and therefore, becomes a suitable alternative of expensive experimental studies.…”