The glass-fiber reinforced thermoplastic pipe (RTP) is more widely used in the oil and gas exploitation due to its excellent performance. In deep-sea engineering, RTPs always sustain pressure, bending, tension or their combinations. The main objective of this paper is to investigate the mechanical behaviour of RTP under combined external pressure and bending moment based on a solid element model. And the strength analysis and buckling analysis are performed. The classical structure of RTP is composed of three main components: an inner high-density polyethylene (HDPE) liner, middle reinforced layers made of thermoplastic composite pipe (TCP) laminates and an outer HDPE cover. In this paper, numerical study considering material nonlinearities of HDPE and TCP laminate is simulated in ABAQUS. Moreover, the TCP laminate shows obvious material anisotropy because of the different orientations of glass crystallographic. It is difficult to set parameters of the material anisotropy nonlinearity directly in ABAQUS. Thus, a UMAT based equivalence procedure is used to simulate the material anisotropy and nonlinearity of the TCP laminate. The paper's emphasis is to analyze the critical responses of RTPs based on the proposed FE model under different loading paths (bending followed by pressure and pressure followed by bending). Then, rotation-pressure interaction collapse envelopes are generated from different loading paths. In addition, the influences of winding methods of TCP laminate and diameter to thickness (D/t) ratio on the mechanical behaviour of RTP are investigated in details. The achievements of this paper can be used to improve the design of RTPs in the industry of deep-sea engineering. Appropriate structure sizes and loading path can avoid premature failure of RTP's structure in the process of installation.
In recent years, with the development of deep-sea technology, glass-fiber reinforced thermoplastic pipe (RTP) has been gradually applied in ocean engineering. The key properities that make RTP an attractive option relative to steel pipe include: more lightweight, more flexible, excellent corrosion resistance, low cost installation, easy recovery processing, etc (Wolters and Friatec, 2006). To date, RTP has been a suitable and a cost-effective solution for offshore applications, such as water injection lines, oil and gas flowlines and static risers up to 6 inches in diameter. RTPs have been produced by many manufacturers, including Pipelife, Coflexip, and Airborne.