Study On Basic Theoretic Of Strain Based Design Of Offshore Pipeline

In the term of offshore oil and gas development, the large distance form the land andlarge depth in sea of this energy make it not convenient for the oil carrier to transport. Soit’s necessary to develop submarine pipeline. However, stress-based designing of submarinepipeline can not meet stability and strength requirements. Therefore the strain-baseddesigning is vital for submarine pipeline designing.Strain based design is a supplement tostress based design. It can apply to nonlinear deformation of pipeline but still can guaranteethe pipeline safety service. Strain based design improved the performance of the utilization ofpipeline materials. Because the submarine pipeline under complex conditions, large strain andlarge deformation are often caused by the complex loads, it is necessary to study the strainbased design of submarine pipeline. Main works are as follow:(1) Strain analysis of S-shape pipeline lyingAnalyze the strain of pipeline when laying the pipelines in deep-sea under condition ofS-shape pipeline lying. Conduct the theoretical calculation of pipe deformation when layingby the cautionary method, and calculate the suspended pipe length by Matlab, and complythe pipeline deformation code by ANSYS. Considering the affect of wave-flow coupling fieldon the pipe laying process, conduct the nonlinear calculation, and finally got the distributionof stress and strain of pipe lying. Consider the affect of laying depth, pipe parameter andother factors on the distribution of stress and strain. By the method of variables controlling Idraw the conclusion that the max strain increases with the depth and parameter increasingwhen laying the S-shape pipeline.(2) submarine pipeline settlement strain analysisConsider foundation settlement as deformation induction factor and conduct strainanalyze on the pipeline. Establish finite element model, considering the coupling effectbetween soil bodies, conduct the nonlinear analysis on the submarine pipeline settlement.Simulate basement pipelines settlement by uniform rules of soil body settlement, consideringthe influence of settle down area, distance between pipelines and the depth of pipelines on thedisplacement and strain of pipeline. By the variables controlling method we draw theconclusion that during the settlement the strain and displacement are maximum when the distance between the subsidence area and the pipeline is0meter. Subsidence of pipelineincrease when then pipeline parameter and wall thickness increase.(3)strain of submarine pipeline on earth shock loadConsider the strain and stress of pipeline along with soil body under earth shock load.Establish pipeline-soil finite model by ANSYS.Considering the coupling of pipeline and soilbody, D-P model are adopted to analyze on the pipeline-soil coupling. Use ANSYS to inputthe existing earth shock wave data and simulate the earth shock. Considering the influence ofsubsidence depth and pipeline parameter on the laying of displacement and strain, draw theconclusion that under the earth shock the strain increases as the pipeline subsidence depthincrease, and strain decreases when the wall thickness increase.