Abstract

The main function of an interlocked carcass is to provide radial stiffness to the flexible pipe, preventing failure modes such as collapse and crushing. The carcass is designed to withstand a specified collapse pressure while attaining minimum flexibility levels, the main parameter for its functionality. This combination of both high radial stiffness and flexibility arises from the interlocked profile and its associated clearances, which are also the main responsible for the highly nonlinear mechanical behavior of the carcass due to the wide range of self-contacts possibilities. In this way, given the complexities of modeling the interlocked carcass considering its exact geometry, most approaches available in the literature adopted simplifying hypotheses, the equivalent orthotropic layer being the most common one. However, with that, important effects from the interlocking are disregarded, such as stiffness variations and stress concentrations. For collapse problems in specific, three-dimensional carcass finite element models have already been developed, but there is nothing similar in the literature for bending loadings. Therefore, the present work proposes two full three-dimensional finite element models of an interlocked carcass, the last one also containing an inner polymeric sheath. For comparison, a third model was also developed, containing just a polymeric sheath. All models were meshed with second-order solid isoparametric finite elements, considering, therefore, all details of the interlocked profile and the self-contacts possibilities. The results are then presented in detail and comparison are carried out, allowing the evaluation of the interlocking effects during bending and how it influences the mechanical behavior of the carcass.

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