Failure analysis of a composite riser pipe under operational and spooling loads

Fibre-reinforced plastic riser pipes are on the cusp of deployment in deep waters where high specific strengths and moduli and corrosion resistance are highly advantageous. In this work, failure analysis is performed for thermoplastic composite pipe (TCP) under loads illustrative of deepwater riser operation by finite element modelling. Temperature-dependent material properties are considered. Different laminate stacking sequences are analysed and a multi-angle stack is shown to be effective for both small and large tension operating scenarios. The bending of TCP at reduced and elevated temperatures, representative of spooling in different environments, is also investigated. Temperature change causes deviation from the symmetry expected between stresses at tensile (top) and compressive (bottom) sides of the pipe under simple bending. It is shown that TCP can be optimised for spooling by orientating unidirectional layers at an 'intermediate' angle that promotes utilisation of in-plane shear strength, rather than fibre or transverse strengths. Since optimising the stacking sequence for operation and spooling are effectively mutually exclusive, large spools will inevitably be required for TCP designed to operate in extreme in-service conditions.