Simulation And Analysis Of Submarine Pipeline Crossing Active Faults

Submarine pipeline is holding an increasing important place in the field of offshore energy exploitation and transmission among countries referring as marine lifeline system. Generally, submarine pipeline needs a long transport distance to complete the task of energy delivery. In that case, pipeline has to pass through areas with high seismic activity and therefore the threat of active faults to the lifeline system is non-negligible. However, few guidelines regarding offshore pipelines crossing active seismic faults are mentioned in the provisions of seismic norms. In order to get insight into the performance of the submarine pipeline subjected to faulting loads, the interacting pipe-soil model is simulated rigorously by employing the finite element software ABAQUS. The main research contents are as follow:(1) Basic model simplification and theoretical hypothesis are introduced to simulate the interacting pipeline-soil system, accounting for nonlinear material behaviors and large strains of both pipeline and surrounding seabed soil. Equivalent spring boundaries are derived for the purpose of preserving accuracy and reducing operation time. The contributions of pipe segments with small deformations by the way of axial stretching and bending to the performance of the research model are calculated.(2) Main failure modes of submarine pipeline under active faults are discussed in present paper and the corresponding safety assessment of pipeline is established based on the theory of strain-based criterion. The comprehensive results of the mechanical behavior of submarine steel pipelines subjected to three types of active faulting loads are conducted and some valuable conclusions are obtained during the investigation.(3) Main factors that influence the mechanical behavior of submarine pipeline subjected to active faults are divided into three classes, including pipe parameters, pipe-soil coupling parameters and seabed soils. The effect laws of the above-mentioned parameters on the strength and deformation behavior of submarine pipeline crossing various active faults are discussed in this paper, and some advices are obtained to enhance the pipeline’s ability to withstand greater fault displacements.(4) Uniform design is introduced to carry out the numerical simulation experiments, and the critical fault displacement is chosen as the pipeline safety evaluation index. Based on the experimental results, analytical expressions for mechanical response of submarine pipeline are established with all influencing parameters are considered. The weight of each influencing factor and the interacting relationships among parameters are also analyzed in this paper.(5) GFRP wraps employed to reinforce submarine steel pipeline crossing active faults are investigated in this paper and the contribution rate compared to non-wrapped conditions is calculated. The effects of the wrap thickness, length, and position relative to the fault plane are analyzed. In addition, the cases where wrapped pipeline passes through faults at various crossing angles are considered.