Partially-plastic theoretical model of thermoplastic composite pipes and comparison of composite failure criteria

Thermoplastic composite pipes (TCPs) are becoming potential alternatives to steel pipes for transporting hydrocarbon and other fluids in the oil and gas industry due to the superior properties including corrosion resistance, light weight, high pressure rating, etc. The cross section of TCPs generally consists of three layers: inner liner, composite laminate, and outer jacket; three layers are fusion-bonded together to form a solid-walled construction. The multi-layered structure and anisotropic material drive the analysis of TCPs much more complicated than those of steel pipes. In the present study, a partially-plastic theoretical model was developed for analysis of TCPs subjected to internal pressures. The theoretical model, benchmarked by FEA simulations, can accurately calculate the stresses which are not uniformly distributed along the radial direction of the TCP. Experiments were conducted on TCPs with the laminate layer of a different thickness. Comparisons of the experimental and theoretical results show that the partially-plastic theoretical model and the fiber failure criterion accurately predict the burst pressure of TCPs of winding angles of +/- 55 degrees. The applicability of Tsai-Hill, Tsai-Wu, and fiber failure criteria were assessed using experimental data. The advantages of the partially-plastic theoretical model and influences of the thickness of the laminate layer were demonstrated using case examples. The present work provides some useful tools and guidance for the design and analysis of TCPs and other composite pressure vessels.