Short-Term Burst Pressure of Large Diameter and High Pressure Reinforced Thermoplastic Pipe

Abstract

Reinforced thermoplastic pipe (RTP), which basically consists of thermoplastic matrix and reinforced layers, has many advantages such as good flexibility, corrosion resistance and long service life. It has been used in oil and gas transportation pipeline industry for several decades, but generally has either low working pressure or small piping size which limits its application range. Recently, a new type of RTP with high design pressure of 6.9 MPa and large outside diameter of 490 mm was manufactured to substitute traditional metallic piping for long distance oil and gas transportation. In this paper, mechanical properties of such RTP, which is composed of four layers’ cross helically wound steel wires in the middle and two layers’ high density polyethylene (HDPE) inside and outside, are studied. Firstly, a multi-layer model was proposed to analyze the stress-strain relationship for the complex reinforcement structure considering the elasticity of both steel wires and HDPE. Further, an analytical procedure was developed to predict the short-term burst pressure (STBP) of high pressure RTP by taking the nonuniformity of reinforced steel wires into consideration. The practical position and nonuniformity of reinforced steel wires were measured by ultrasonic phased array technique. Then, short-term burst tests were conducted to validate the proposed model. Hoop strains at different internal pressures were measured and a good agreement with theoretical results was obtained, which verifies the effectiveness of the presented model. Finally, some differences of analytical and experimental techniques for STBP between normal RTP and RTP with large diameter and high design pressure were further discussed.