A Fracture Mechanics Study on Pressure Armour Wire in Flexible Pipes

Flexible pipes are essential in offshore oil and gas production, offering adaptability and resilience in challenging subsea environments. Among their critical components, the pressure armour wire is responsible for withstanding hoop stresses generated by internal pressure. However, these pipes face failure modes such as fatigue, stress corrosion cracking (SCC), and degradation from CO2 exposure, especially in pre-salt fields. This paper employs fracture mechanics principles, including Linear Elastic Fracture Mechanics (LEFM) and Elastic-Plastic Fracture Mechanics (EPFM), to assess these failure risks and explores the role of Finite Element Analysis (FEA) in evaluating structural integrity. Analytical, hybrid and Fracture Mechanics based (FM-based) FEA methods to validate the model and analyze crack-driving forces (CDFs). Analytical thin- and thick-wall theories for hoop stress were compared against FEA results, confirming the inadequacy of thin-wall theory for thick-walled components and the validity of FEA for capturing stress variations. Simplified and complex geometries were also assessed, with complex models demonstrating reduced conservatism due to their ability to capture mitigating factors like energy redistribution and adjacent wire support. Key findings reveal the benefits of compressive residual stresses in increasing allowable crack sizes by reducing CDFs, thereby enhancing structural performance. While hybrid methods aligned closely with FM-based FEA in most scenarios, critical crack positions required the detailed insights provided by FM-based solutions. These results highlight the need for a balanced application of analytical, hybrid, and FM-based methods depending on component criticality and complexity. This study emphasizes the importance of FM-based FEA in ensuring the reliability of flexible pipes, offering a robust framework for addressing failure risks and advancing structural integrity assessments in offshore applications.