Numerical analysis of the mechanical behaviour of reinforced thermoplastic pipes under combined external pressure and bending

Reinforced thermoplastic pipes (RTPs) are promising design solutions for deep-water riser applications due to their light weight, high performance and good spoolability. For such applications, RTPs experience significant ambient pressure and sustain bending and/or tension loads during the installation and operation phases. Normally an RTP is composed of an inner Polyethylene (PE) liner, reinforced layers made from fibre-reinforced PE composites and an outer PE cover. The mechanical behaviour of such an RTP when it has been subjected to combined external pressure and bending has been studied through finite-element analysis (FEA). The nonlinear mechanical behaviour of both PE and the fibre-reinforced PE composites has been modelled by developing numerical algorithms that reflect the strain-dependent mechanical characteristics of PE. These algorithms are implemented in the analysis tool used, Abaqus/Standard, with the user subroutine, UMAT. The proposed FE model could accurately simulate the buckling and post-buckling response of the RTP and predict its failures under the combined external pressure and bending. Rotation-pressure interaction collapse envelopes of the RTP in different loading paths are generated. Additionally, the effects of ply angles, loading paths and diameter-to-thickness (D/t) ratios on the performance of the RTP under this loading case are investigated. The results obtained could be used to improve the design of RTPs for deep-water riser applications in the offshore oil and gas industry.