Structural response and damage assessment method for subsea pipe-in-pipe subjected to anchor impact

The pipe-in-pipe system is widely used in the development and transportation of offshore oil and gas resources. The damage caused by anchor impacts on the pipe-in-pipe system has long been a focal point and challenge in both engineering and academic fields. Numerical simulation method is employed to investigate the impact process of anchors on pipe-in-pipe systems, revealing the variation patterns of pipeline deformation response over time. The structural response of the pipe-in-pipe system to dropped anchor impacts is studied from multiple perspectives, including deformation, energy, and load transfer. The influence of pipe-in-pipe characteristic parameters, anchor characteristic parameters, centralizers, and bulkheads on the extent of impact damage is analyzed, establishing a relationship between the absorbed energy and the damage to the pipe-in-pipe. The results indicate that the impact energy primarily depends on the mass and velocity of the anchor. Energy is conserved during the impact process. It is found that even with different anchor masses and velocities, the extent of damage to the pipe-in-pipe system remains the same if the impact energy is identical. High-strength steel, large diameter, and thick-walled pipelines exhibit better resistance to impact loads. Additionally, centralizers and bulkheads mitigate the impact damage to the pipe-in-pipe system. Finally, an evaluation method for pipe-in-pipe impact damage due to dropped anchors is proposed. It is discovered that the assessment method for pipelines impacted by dropped anchors in the DNV-RP-F107 standard tends to be conservative when the impact energy is high. The findings of this study provide technical support for the integrity management of pipe-in-pipe systems.