In order to investigate the tensile fatigue performance of fiber reinforced thermoplastic pipe (FRTP), initially, a three-dimensional finite element model was generated, followed by the validation of the results using an FRTP experiment. The model utilized user-defined mechanical material behavior (UMAT) program to elucidate the essential relationship between composite pipe and attenuation of mechanical properties of the element. For numerical assessment of tensile fatigue failure, the stress and failure element were identified, and stiffness attenuation due to tensile load on FRTP was predicted. In addition, the mode of FRTP damage for four different fatigue loads and the resulting stress levels were analyzed by the proposed model, by which the law of stiffness attenuation in FRTP implemented in the experiment was explained.
As the depth of offshore oil and gas exploitation increased, the required length for riser also increased. Compared to traditional rigid risers, flexible risers can withstand larger displacements and more complex loads due to their smaller bending stiffness and lighter weight and thus provides significant advantages in deepwater oil and gas engineering.
Flexible pipes are divided into non-bonded and bonded flexible pipes. The sectional structure of a bonded flexible pipe consists of three layers -the inner, reinforced, and outer layers. The functions of different layers include inner layer transports of internal oil, gas, and other fluid media, reinforced layer acts as the main bearing structure (Lou et al., 2020), and outer layer prevents seawater intrusion and reduces external impact.
Fiber-reinforced plastic incorporated composite filament-wound pipes have many inherent advantages over other pipes, such as high strength, better specific stiffness, robust corrosion resistance, and adequate thermal insulation. Hence, these pipes have far-reaching prospects in the field of ocean engineering (Tarakçioğlu et al., 2005). The reinforced layer comprises winding multi-layer reinforced fiber tapes which are In recent years, there has been an increased interest in the design (Pham et al., 2016), manufacture (Frketic et al., 2017), and applications (Beyle et al., 1997; Tarnopol'skii et al., 1999) of FRTP due to its extensive use in the marine environment. Investigations show that the mechanical properties of composite pipes were affected by the combination of materials, geometry of components, and process of production. In addition, these pipes have better mechanical properties as a result of adjusted fiber winding angle, content, and preload (Colombo and Vergani, 2018; Guedes, 2006, 2009; Xia et al., 2001a, 2001b; Xing et al., 2015).
