Understanding the Behavior of the Flexible Pipe Outer Sheath at the Expander Tip of the End-Fitting

Abstract Flexible pipes play an important role in the offshore and subsea industry, particularly in oil and gas exploration and production. The pipes are essential for transporting oil and gas from deep subsea environments to surface facilities. The integrity of the outer sheath of a flexible pipe is crucial for maintaining a leak-proof annulus that protects the metallic layers inside from corrosion, directly impacting the performance, safety, and reliability of the entire system. This research investigates the behavior of the outer sheath, focusing on the region near the expander tip where localized straining can occur. To better understand this behavior, a simplified analytical model is proposed, which characterizes the stick-slip behavior of the outer sheath in this region. The model provides a generalized understanding of the behavior that extends beyond case-specific finite element studies, making it broadly applicable to different pipe designs and operational scenarios. Using a combination of analytical and numerical methods, the research considers key factors including hydrostatic pressure, pipe loading conditions, and expander tip design. The results show a strong correlation between the simplified analytical model and finite element analysis, validating the utility of the model. The research provides a generalized understanding of the outer sheath behavior at the expander tip, helping to understand potential failures and guide design principles to reduce local strain in this region.