Structural integrity and failure mechanisms of thermoplastic composite pipes for offshore applications: insights from compressive and flexural testing.

Okolie, Obinna; Faisal, Nadimul Haque; Jamieson, Harvey; Mukherji, Arindam; Njuguna, James

Abstract

This research investigates the structural integrity and mechanical behaviour of a thermoplastic composite pipe (TCP) that is particularly used in the offshore energy industry. The TCP offers enhanced strength and high strength-to-weight ratio ideal for applications subject to varying loading conditions. Despite its structural benefits, the composite pipe is susceptible to delamination and other damage modes that compromise its performance. This study addresses the limited research on curved composite structures, especially in the context of debonding and stress distribution, by focusing on the behaviour of the TCP under compressive and flexural loading conditions. Non-destructive testing (NDT) methods, including X-ray computed tomography (XCT) and ultrasonic inspection, are employed to characterize internal damage mechanisms from these tests such as microcracking, fibre breakage, and matrix deformation at a microstructural level. Flexural testing indicates that failure initiates through tensile cracks in the outer layers, while compression testing reveals progressive damage through delamination, matrix degradation, and fibre buckling. The pipe stiffness and elastic modulus were ascertained to be 2184.2MPa and 13.18GPa respectively. Microstructural analyses of compressive failure further reveal the complex failure pathways. This shows that matrix cracking and delamination are primary failure mechanisms driven by the polymer matrix's limited fracture toughness and the complex stress interactions within the laminate. Delamination and matrix cracking are localized yet progressive, exacerbating the fibre to matrix separation which impact load-bearing capacity of the pipe. These findings underscore the importance of optimizing fibre orientation, matrix-fibre adhesion, and layer configuration to enhance structural toughness. This comprehensive evaluation of mechanical performance and failure mechanisms provides valuable insights for optimizing the manufacturing processes of TCP, aiming to improve durability, reduce material waste, and enhance long-term reliability in demanding service environments.

Citation

OKOLIE, O., FAISAL, N.H., JAMIESON, H., MUKHERJI, A. and NJUGUNA, J. [2025]. Structural integrity and failure mechanisms of thermoplastic composite pipes for offshore applications: insights from compressive and flexural testing. Engineering failure analysis [online], In Press, article number 109775. Available from: https://doi.org/10.1016/j.engfailanal.2025.109775

• Journal Article Type: Article
• Acceptance Date: May 28, 2025
• Online Publication Date: Jun 13, 2025
• Deposit Date: Jun 2, 2025
• Publicly Available Date: Jun 14, 2026
• Journal: Engineering failure analysis
• Print ISSN: 1350-6307
• Electronic ISSN: 1873-1961
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Article Number: 109775
• DOI: https://doi.org/10.1016/j.engfailanal.2025.109775
• Keywords: Composite materials; Multilayer structures; Thermoplastic composite pipes; Delamination; Matrix cracking; Inter-laminar debonding; Manufacturing process optimisation; Damage characterisation
• Public URL: https://rgu-repository.worktribe.com/output/2872439