Numerical Simulation Of Influence Of Pipe-soil Elastic Slip On Submarine Pipeline Walking

The submarine pipeline is the "lifeline" of oil and gas resources transportation,so its stability is crucial.The opening and closing process of the submarine pipeline operation makes the submarine pipeline suffer from the temperature cycles of heating up and cooling down,and uneven expansion and contraction of the pipeline,which causes instability of the pipeline walking and endangers the stability of the submarine pipeline.Most of the studies assume that the pipe-soil interaction is rigid-plastic,which uses a single friction coefficient to describe the pipe-soil interaction.But in actual situation,pipe-soil interaction is closer to the elastoplastic behavior.This paper focuses on the influence of elastic slip on the pipeline walking behavior of HTHP submarine pipelines.Firstly,the numerical model of submarine pipeline walking on rigid seabed is established under the finite element software ABAQUS.The accuracy of the model is verified by comparing with the analytical solution.Secondly,the numerical model of submarine pipeline walking considering the elastic slip between pipe and soil is established to analyze the influence of elastic slip on pipeline walking rate.Finally,a numerical model of submarine pipeline walking considering temperature gradient is established.The temperature gradient is coupled with different tension forces to study the variation rules of pipeline walking rate.The specific research conclusions are as follows:1)The elastic slip between pipe and soil affects the submarine pipeline walking behavior.The distribution of axial soil resistance,axial force,axial strain and axial displacement of the pipeline changes,and the virtual anchor point will also produce displacement.The increase of elastic slip during temperature cycles leads to the decrease of axial displacement of the submarine pipeline and the decrease of pipeline walking rate.The change between the pipeline walking rate and the elastic slip is negative exponential,and the inflection point occurs when the elastic slip is 0.05 m.2)The pipeline length,tension force and friction coefficient will also affect the pipeline walking.When the elastic slip of pipe-soil is the same,the pipe length increases and the pipeline walking rate decreases;the tension force of riser increases and the pipeline walking rate increases;the friction coefficient increases and the pipeline walking rate decreases.When the pipe length is the same,the pipline walking rate decreases with the increase of elastic slip;When the tension force is the same,the pipeline walking rate decreases with the increase of elastic slip.When the friction coefficient is the same,the pipeline walking rate decreases with the increase of elastic slip,and finally tends to zero.3)The internal temperature gradient of the submarine pipeline during oil and gas transportation has an impact on the submarine pipeline walking considering elastic slip.In the condition of this case and only temperature is considered,when the elastic slip is less than 0.03 m,the pipeline walking rate remains unchanged.When the elastic slip is greater than 0.03 m,the pipeline walking rate decreases with the increase of the elastic slip.The pipeline walking behavior combined temperature gradient and tension force is studied.The two different situations of tension and temperature gradient in the same and opposite directions are studied respectively.The results show that when the tension and temperature gradient are in the opposite direction,the pipeline walking rate of the submarine pipeline is small.When the elastic slip is less than 0.03 m,the tension promotes the pipeline walking,as the temperature gradient plays a restraining role.When the elastic slip is greater than 0.03 m,the tension inhibits the pipeline walking,as the temperature gradient promotes it.When the tension is in the same direction as the temperature gradient,the pipeline walking rate is large,and the pipeline walking rate decreases approximately linearly with the increase of elastic slip.