Mechanical Analysis Of Critical Sealing Condition And Sealing Performance Optimization On Clamping-pressing Type Subsea Pipeline Connector

The subsea pipeline is a most effective method for transporting marine oil and gas resources from seabed to land.However,the marine environment is very complex,which causes that the subsea pipeline is damaged.The leakage of oil-gas resource will badly pollute the marine environment.The fast repair connection technology for subsea pipeline is monopolized by Euro-American Countries,which has a serious effect on the development of ocean engineering.With the quickening pace of exploiting marine oil-gas resources in China,it is the great practice significance that the theory and method in the subsea pipeline connection are researched.For the requirement of high-efficiency repairment and reliable connection of subsea disabled pipeline,the structure of clamping-pressing type subsea pipeline connector is presented,which is belong to the non-gasket sealing method.Aiming at the critical sealing condition and structural optimization of clamping-pressing type subsea pipeline connector,this paper uses theoretical analysis and numerical simulation to study the micro sealing model,critical sealing condition,structural parameter sensitivity and multi-objective optimization based on sealability.The research of metallic micro sealing mechanism is presented.On the stage of elastic-plastic deformation,the mechanical property of single micro peak is studied,and the mechanical models between contact area and contact force and contact distance are deduced.The micro static sealing model of contact surfaces is established.According to the volume conservation mechanism of metallic material,the real contact area and contact pressure on sealing surface are solved.The contact area and contact pressure affected by roughness and yield strength are analyzed.The contact process of two micro rough surfaces is simulated by the finite element method and the results verify the validity of micro static sealing model.Aiming at the sealing condition of clamping-pressing type subsea pipeline connector,the solution of critical mean contact pressure on sealing surface is studied.Analyzing the contact pressure distribution on sealing surface,the critical condition realizing reliable seal is established.Aiming at the mechanical model of pipeline surface under uniform pressure,the expression between pipeline displacement and stress and uniform pressure is deduced by stress function method and is verified by numerical simulation.Based on the superposition principle of elasticity,the expression of critical mean contact pressure is solved by approximation method.The effect of pipeline wall thickness and sealing surface width on critical mean contact pressure is analyzed,which is the lower limit value of constraint variables in the optimal design of connector.Aiming at the problem of more design variables of clamping-pressing type subsea pipeline connector,the sensitivity analysis of structure parameters is presented.The contact pressure,contact uniformity and spring back are defined as evaluation parameters.The finite element model of connector is created,which solves the relation between evaluation parameters and structural parameters.The sensitivity of evaluation parameters and structural parameters is solving,based on the results,and the structural parameters of larger sensitivity are confirmed as design variables,which can reduce the design space and improve computational accuracy and efficiency for optimization design.In order to improve the connector sealability,the connector is optimized by the multi-objective genetic algorithm.The fundamental of genetic algorithm is analyzed,and the optimization model of connector is established,with the contact pressure variances on two sealing surface as objective function,the mean contact pressures and maximum plastic strains as constraint variables.The approximate equations between both objective functions and constraint conditions and design variables are obtained by the radial basis function method.The structural parameters of two sealing parts are optimized,and the optimum structure can be obtained by the Pateto solutions.The objective function and constraint variable of optimized connector are compared with that of no-optimized connector,which verifies the optimal design improves the sealing performance of connector.The sealing ability of optimized connector connecting pipeline with different materials is analyzed,which can be used to guide the practical application of connector.In order to verify the validity of micro static sealing model and multi-objective optimization,the experimental results of microtopography deformation on sealing surface,indentation on pipeline surface and internal pressure of connectors are analyzed.The microtopography deformation on sealing surface of different roughness is observed by the scanning electron microscope.The contact rate of true area is compared with that obtained by the theoretical model,and the source of error is analyzed.The optimized connectors and no-optimized ones are sectioned with axial plane.The indentations are compared and the reason is given.The test platform of internal pressure is set up and the sealing ability of optimized and no-optimized connectors is compared.Meanwhile,the experiments of tension and fatigue are carried out,which aim is to test the ability of optimized connector resisting the complex external load.The test results verify the feasibility of the method solving critical mean contact pressure and the method of multi-objective optimization design.The clamping-pressing type subsea pipeline connector uses the static sealing structure of double sealing rings and can resist higher internal pressure and external load,which provides a theoretical basis for connector design with various dimensions and promotes the development of deepwater oil-gas pipeline connection technology.