Safety and integrity of submarine pipelines/flowlines under interaction of fishing trawl doors are investigated for the 16" and 36" pipe. The trawl door pull-over loads are based on experimental results. Global responses are calculated with respect to normal stresses and lateral displacements for different pipeline conditions, using time-domain simulations. Local response analysis is performed with respect to indentation considering both elastic and plastic deformation. Serviceability, fatigue and ultimate limit states are established considering pigging requirement, low cycle fatigue, yielding, excessive lateral displacement and local deformation. Safety is assessed based on the results from global and local response analyses and realistic uncertainty measures.
Submarine pipelines and flowlines play an important role in offshore oil and gas transportation. Structural failure of steel pipes will result in serious consequences, such as release of transported hydrocarbons, pollution to the environment, and heavy costs due to repair and even shut down of the transportation system. Previous submarine pipeline/flowline in-service records indicate that a major cause of pipe failure is due to interference of the third party activities (Andersen and Misund, 1983, Cannon et al., 1985, Mandke, 1990). For relatively small diameter pipes laid cross the areas with dense fishing traffic, impacts from fishing trawl doors may be critical to the pipe integrity. To avoid external interference, it is possible to protect pipelines or flowlines from external impacts by simply trenching or burying the exposed pipes, which may often lead to an unacceptable increase in costs. A careful global and local pipe response analysis together with an appropriate safety evaluation, however, may avoid such expensive actions and result in a cost benefit design. In this paper, time domain dynamic global response analysis and static local response analysis are performed. Sensitivity analysis is made to identify the important parameters governing the response characteristics.
