Study On Instability Mechanism Of Reinforced Thermoplastic Pipe Under Axial Compression

Reinforced thermoplastic Pipe (RTP) is a new type of composite pipe employed in oil&gas exploration and typically it consists of a polymeric liner, a structural layer and a polymeric cover. The structural layer of reinforced thermoplastic pipe is reinforced by aramid fiber in the helically wound reinforced preformed tape where the encapsulation is a thermoplastic resin. Pipe may be subjected to axial load during installation and operation. Pipe may collapse under axial compression and then the whole pipeline fails. This thesis focuses on the instability mechanism of reinforced thermoplastic pipe, and its main contents are summarized as below:1) RTP prototype experiments and material experiments for HDPE. Axial compressive experiments and axial tensile experiments for RTP pipes were conducted, and the compression-shortening curves and tension-extension curves were obtained. Furthermore, tensile experiments and compressive experiments for HDPE, which is the main raw material of RTP, were conducted. The nominal stress-nominal strain relationship was determined from these material experiments.2) Mathematical analysis on global instability of RTP under axial compression. Based on non-linear ring theory, the M-P-Φ relationship for RTP pipe cross-section under combined bending and compression was determined. Furthermore, y-θ-Φ relationship was determined by numerical integration method. Finally, the ultimate bearing capacity of RTP under axial compression in global instability case was solved and the results were verified by finite element analysis.3) Global instability finite element analysis for RTP under axial compression. By conducting finite element analysis, the buckling modes and post-buckling properties of RTP global instability under axial compression were determined. Furthermore, more finite element analysis was conducted to determine how some parameters influenced the ultimate bearing capacity of RTP under axial compression. These analyzed parameters were pipe wall-thickness, amplitude of initial imperfection, ovality of pipe cross-section and slenderness ratio.4) Local instability finite element analysis for RTP under axial compression. By conducting finite element analysis, the buckling modes and post-buckling properties of RTP local instability under axial compression were determined. Furthermore, more finite element analysis was conducted to determine how some parameters influenced the buckling mode of RTP under axial compression. These analyzed parameters were diameter-thickness ratio and slenderness ratio.