Research On Axial Pipeline Walking Under High Pressure And High Temperature

The development of deep-water marine resources is the main growth point of Chinese future oil&gas resources.Submarine pipeline is known as “the lifeline of marine oil&gas resources”,playing an important part of submarine oil&gas gathering and transportation system.This paper presented a new calculation method of multi factor induced pipeline walking in submarine pipelines when the axial pipeline-soil interaction model was simplified as a constant.Also,a novel bi-liner axial soil resistance model adopted by unburied pipeline lying on Bohai sand was proposed according to the result of enormous indoor axial pipe-soil resistance model tests.The effect of mobilization displacement,peak resistance,and internal pressure on pipeline walking and best pipeline-anchoring position were discussed by using finite element method.The main contents and conclusions are as follows: The present models of pipe-soil interaction were concluded.1.The mechanism of three single factors leading to the flowlines axial directional movement,which were steel catenary riser(SCR)tension,sloping seabed and thermal transient,was illustrated.Numerical models of multi factors induced axial directional movement were established.A new calculation method of multi factor induced axial directional displacement in submarine pipelines was presented.2.The present models of axial pipe-soil interaction were concluded and a novel bi-liner axial soil resistance model adopted by unburied pipeline lying on Bohai sand was proposed according to the result of enormous indoor axial pipe-soil resistance model tests.The results indicate that the number of axial movement cycles and the movement rate have no obvious effect on the axial mobilization displacement and axial peak resistance.In contrary,axial mobilization displacement becomes larger with the increasing of pipeline outside diameter,which is 0.01D~0.04 D.Then axial peak resistance is a function of axial resistance force factor,which is about 0.51~0.62 when pipeline is moving axially on the sand.3.Pipeline walking phenomenon under bi-liner axial soil-pipeline resistance model was analyzed with finite element software,ABAQUS and the effect of mobilization displacement,peak resistance,internal pressure on pipeline walking and best pipeline-anchoring position were discussed.The finite element analysis shows that pipeline walking distance will increase with the decreasing of axial mobilization displacement and the axial peak resistance.With the increase of internal pressure,pipeline walking distance induced by SCR will decrease and that induced by thermal transient will increase.The maximum effective axial force in pipe will become smaller with the pipeline-anchoring point moves from the ends of the pipe to the midpoint of the pipe.