Impacts of ocean current and seabed friction on the picking-up and laying-down processes of oil and gas pipelines

Based on engineering practice of the picking-up and laying-down processes of offshore pipelines, a finite element model was established. On the basis of the model, methods and steps of the picking-up and laying-down operations were determined, and the impacts of currents and seedbed friction on the two operations were studied. The shape and stress distribution of the pipeline under the influences of longitudinal current, lateral current and seabed friction when picked up and laid down were analyzed using finite element analysis software. The results show that the longitudinal current has almost no effect on the pipeline shape and stress distribution in the picking-up and laying-down processes, while the lateral current results in significant deformation of the pipeline in the horizontal plane and raises the overall stress level of the pipeline. The friction between the seabed and the pipeline impedes the lateral displacement of the pipeline when it is laid down. The rougher the seabed, the smaller the overall lateral displacement of the pipeline is. When the pipeline reaches the equilibrium state after it is laid down, the friction between the pipeline and the seabed becomes larger with the increase of the friction coefficient.