Research On Deep-sea Pipeline Lateral Global Buckling And Axial Walking Due To High Temperature And Pressure

Submarine pipelines are frequently used to transfer oil and gas in offshore engineering,and the cost of pipeline systems takes a great proportion in the total investment of the offshore oil development project.In order to prevent pipeline to be blocked by the condensation of oil,pipelines are usually heated and pressurized during transporting.The high temperature and pressure may cause large compressive stress accumulating in the cross-section.Since deep-sea pipelines have longer conveying distances than those of the shallow-sea pipelines,deep-sea pipelines exhibit obvious larger temperature and pressure load.In addition,the deep-sea pipeline is usually unburied and suffers smaller soil restriction,and the deep-sea is more likely to deforme due to the compressive axial stress caused by large temperature and pressure.The lateral and axial deformations of a deep-sea pipeline are lateral global buckling and axial pipeline walking.The lateral global buckling can release the compressive and reduce the risk of the whole pipeline system.But the excessive deformation will produce large strain and harm the intergrity of corss-section.Obtaining an accurate prediction of lateral deformation form is important for optimizing the pipeline design and reducing engineering cost.The pipeline walking is caused by cyclic loading,and large displacement towards to one direction occurs in this process.The pipeline walking threatens the safety of pipeline endings.The walking rate of a deep-sea is significant in practice.Calculating the walking rate of a pipeline and taking protection measures is a precondition for maintaining the long-term stable of pipeline systems.This paper analyzed the lateral global buckling and axial walking of a deep-sea pipeline with analytical calculating,numerical simulation and model tests.The main contents are as followed.(1)A reliable simulation model for calculating the lateral global buckling deformation was established.Several nondeterministic parameters are discussed.The influence of initial penetration on soil resistance was discussed in the model tests.(2)The distributions of plastic strain which threatens the intergrity of pipeline corss-section were obtained,and fitting functions for cauculating plastic strain with the variation of key parameters were established.(3)The numerical simulation of pipeline walking was proposed.Three simple equations for modifying the classical theory solution were obtained with numerical simulation method.These equations can be used to calculate the situation that the soil friction coefficients in heating and cooling process are two different content numbers.(4)A method to predict the walking rate of a pipeline considering soil resistance varying with the passing of time was proposed.The soil resistance on pipeline was regarded as the function of time,and the walking rate prediction formula was deduced based on accumulated value of every tiny moment.Therefore,the solution is suitable for any soil models.(5)The walking mechanism for a pipeline connected with a sliding structure exhibiting different soil resistance in different directional sliding was found,and the analytical solution was deduced.A novel walking controlling mechanism was proposed based on this phenomenon.And a new walking compensation device was designed to reduce the total walking rate.