Analysis of the mechanical properties of a reinforced thermoplastic pipe (RTP)

This paper describes the analysis of a long length reinforced thermoplastic pipe. For this new class of pipe, which is constructed of a polyethylene liner pipe over wrapped with two layers of non-impregnated twisted aramid cords, peculiar deformation behaviour was observed when a pipe was pressurised. This behaviour was found to be a result of a difference in cord-slack between the two reinforcement layers in conjunction with an unbalanced torsion moment generated by the two reinforcing layers. Cord slack is a certain surplus length of the reinforcing cords relative to the pipe geometry. The cord-slack is estimated for the two different layers and first incorporated into an earlier published model, based on a plane stress characterisation. As no substantial improvement has been achieved by this approach, a new model based on a plane strain characterisation is introduced. This model shows good agreement with the experimentally determined strains for the hydrostatic pressure load-case.