Marine thermoplastic riser reinforced with novel fibers have broad prospects in deepwater oil and gas development due to their advantages such as coilability,corrosion resistance,fatigue resistance,and lightweight.Thermoplastic riser exhibit the anisotropy of composite materials,stress coupling effects,complex constitutive relationships,and withstand floating body motion and complex marine environmental loads,with failure modes yet to be clarified.Focusing on the ultimate bearing capacity of fiber-reinforced thermoplastic riser under axisymmetric loading,theoretical derivations of steady-state heat conduction and thermal stress in thermoplastic pipes are conducted.Solutions for steady-state temperature and stress distributions are obtained.Analytical solutions for radial displacement of the pipe body under any temperature load are provided for the first time.Radial,axial,circumferential,and shear stresses are directly solved.Failure of thermoplastic pipes is determined using the isotropic layer Von Mises and anisotropic layer maximum stress(Max Stress)criteria or the Tsai-Hill criterion.Based on stress distribution,failure criteria,and bisection method,the ultimate load of thermoplastic pipes is calculated.Temperature load,fiber layup angle,and thickness-to-diameter ratio significantly affect stress distribution in the pipeline.Different temperature loads change the trend of failure index along the radial direction.Increasing axial tension increases the failure index of thermoplastic pipes.Different failure criteria result in differences in pipe body failure determination.Lower temperatures,smaller fiber layup angles,and larger thickness-to-diameter ratios result in higher bearing capacity of the pipeline under axial tensile loads.
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