Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Numerical and Experimental Research on Tensile Fatigue Performance of Fiber Reinforced Thermoplastic
Pipe (FRTP)
Weixing Lianga Min Loua, Chen Zhanga and Jiaming LiuaaCollege of Petroleum Engineering, China University of Petroleum (East China)

Qingdao, Shandong, China

bonded together by heat, provides strength to the layer.

ABSTRACTIn 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 anFRTP experiment. The model utilized user-defined mechanical material
behavior (UMAT) program to elucidate the essential relationshipbetween composite pipe and attenuation of mechanical properties of theelement. For numerical assessment of tensile fatigue failure, the stressand failure element were identified, and stiffness attenuation due totensile 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.

KEY WORDS: Thermoplastic pipe; flexible riser; tensile fatigue;
residual stiffness.

Figure 1. Schematic diagram of FRTP structure.
In recent years, there has been an increased interest in the design (Phamet al., 2016), manufacture (Frketic et al., 2017), and applications (Beyleet al., 1997; Tarnopol'skii et al., 1999) of FRTP due to its extensive use
in the marine environment. Investigations show that the mechanicalproperties of composite pipes were affected by the combination ofmaterials, geometry of components, and process of production. In
addition, these pipes have better mechanical properties as a result ofadjusted fiber winding angle, content, and preload (Colombo andVergani, 2018; Guedes, 2006, 2009; Xia et al., 2001a, 2001b; Xing etal., 2015).

INTRODUCTION
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.

Many scholars have studied the fatigue properties of fiber-reinforced
composite pipes through fatigue experiments as it can inherently andaccurately observe the evolution and mechanism fatigue failure ofmaterials. While Kaynak and Mat (Kaynak and Mat, 2001) and Joseph
and Perreux (Joseph and Perreux, 1994) studied the fatigue behavior ofglass fiber/epoxy resin composite pipe during cyclic axial loading, anddeveloped a damage model based on S-N curve, Gemi et al. (Gemi et al.,2009) studied the same (±75° and ±55° pipes) for cyclic internalpressure and obtained the S-N curve.

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 thefield of ocean engineering (Tarakçioğlu et al., 2005). The reinforced
layer comprises winding multi-layer reinforced fiber tapes which are

The effect of combined loads on fatigue performance of fiber-reinforced
composite pipes has gained attention in recent years. In this aspect,Corresponding author.

E-mail address: shidaloumin@163.com (Min Lou)1853