Study On Active Global Buckling Control Method For Deep-sea Pipeline Structures

With the development of offshore oil and gas exploitation towards deep and ultradeep seas,deep-sea pipelines are generally laid bare on the seabed.In order to ensure the fluidity of crude oil,they will bear the combined action of high temperature above100℃ and high pressure inside the pipeline in the process of oil transportation.Under the working conditions of high temperature and high pressure in deep sea,single-layer pipeline can no longer meet the requirements of design and transportation.As an important part of "973" National Key Basic Research Development Program(2014CB046801),"Research on Extreme Load Action Mechanism of Deep-sea Underwater Oil and Gas Transport System Structure",this paper studies in detail and systematically the active control method for global buckling control of deep-sea pipelines by means of experimental analysis and numerical simulation.The mechanism and validity of the mechanism can obtain the buckling and deformation law of deep-sea pipelines under active control,thus laying a theoretical foundation for effective buckling control of deep-sea pipelines.The specific research contents are as follows:Based on the experimental study of 9 groups of pipe-in-pipe structural pipelines with horizontal initial defects,the influence of initial defects on pipelines during oil temperature and thermal loading is revealed by taking the amplitude and wavelength of defects as parameters.A reasonable finite element model is established and the initial defects,pipe-soil interaction and alignment are obtained by parameter analysis.The influence of ring height and number on the overall buckling critical force of pipeline is studied,and the calculation formula of the overall buckling critical force considering the friction between the central-outer pipe and the pipe-soil is obtained.Compared with the experimental results,it is found that the accuracy is good,which can provide a corresponding reference for pipeline design.Based on the phenomena of dynamic effects during the whole thermal buckling experiments,an accurate finite element model was established and validated reasonably.The influence of pipe diameter,initial defect and pipe-soil interaction on the dynamic effect of pipeline buckling were analyzed.The relationship between each factor and critical buckling force,lateral ejection velocity,lateral displacement and overall kinetic energy of pipeline was found,and an effective method to control the dynamic effect has been put forward.The global buckling behavior of pipes under active control of sleeper-serpentine laying was studied by 10 specimens expermental,and the evolution law of global buckling of pipes under different wavelength and amplitude parameters were obtained.An accurate numerical model of overall buckling is established by considering the dynamic solution method of artificial damping,and the laying shape of pipes is analyzed.The influence of the properties of sleepers and seabed on the global buckling of the pipeline was studied.The formula for calculating the critical buckling force of this kind of pipeline was deduced theoretically and compared with the experimental results,which provides a reference for the design of this kind of pipeline.In view of the axial displacement of the pipeline under the uneven temperature field,the relevant research on sleeper continuous serpentine laying is carried out.By comparing with the straight pipeline,it is found that the continuous horizontal initial defect can effectively reduce the axial movement of the pipeline,and the control mechanism is discussed.According to the characteristics of sleeper continuous serpentine laying,the bending radius value of the pipeline is analyzed and the limit value is obtained.The active control method of sleeper-distributed buoyancy(SDB)was proposed,and the global buckling characteristics of pipe-in-pipe under sleeper-distributed buoyancy method were studied.The finite element model of was established,and the accuracy of the model has been verified.The length of buoyancy block,friction coefficient of pipe-soil,initial defects,stiffness ratio of inner and outer pipes,and the number of middle rings were analyzed.The formula of critical buckling axial force and lateral displacement of pipeline is deduced.The verification results show that the formula has high accuracy and meets the requirements of Engineering design.