Offshore Pipeline Stress and Stability Analysis in the Gulf of Guinea

Abstract

The Gulf of Guinea, a critical hub for global offshore hydrocarbon production, presents unique challenges for subsea pipeline integrity due to its complex environmental conditions, including deep waters, soft seabed soils, and dynamic metocean forces. This research conducts a comprehensive stress and stability analysis of an offshore pipeline in this region to ensure safe and reliable operation. The study employs an integrated methodology, combining rigorous analytical models prescribed by international design codes (DNV-OS-F101, DNV-RP-F109, ASME B31.3) with advanced three-dimensional Finite Element Analysis (FEA) in ANSYS Workbench. A representative pipeline configuration, featuring API 5L X60 steel material, was analyzed under region-specific operational and environmental loads, including internal pressure, thermal gradients, hydrodynamic forces from waves and currents, and geotechnical interactions. The investigation systematically addressed the influence of pipeline geometry, particularly the Diameter-to-Thickness (D/t) ratio, and assessed the impact of the Gulf of Guinea's specific environmental parameters. Key findings demonstrate that the pipeline design is stable under a 100-year extreme storm event, with a safety factor of 2.05 for on-bottom stability. The maximum von-Mises stress of 278 MPa remains well within the allowable limit for the material, validating the selected wall thickness. The study reveals a non-linear, critical relationship between the D/t ratio and induced stress, defining a safe design window for local conditions. Furthermore, hydrodynamic analysis identifies current velocity as the most sensitive environmental parameter governing pipeline stability. Fatigue assessment, based on cumulative damage (Miner’s Rule), indicates a damage ratio of 0.67 over a 25-year design life, confirming adequate fatigue resistance. This research concludes that the integrated analytical-numerical approach provides a robust and validated framework for pipeline integrity assessment in the Gulf of Guinea. The main contributions to knowledge include the development of this region-specific methodology, the quantification of critical parameter interactions, and the provision of validated design benchmarks. The study recommends the adoption of such integrated analysis in industry practice, enhanced data acquisition for regional inputs, and the development of focused integrity management programs to mitigate long-term risks, thereby supporting safer and more sustainable offshore energy infrastructure in the region.