| Connection of the equipment of deep-sea oil and gas field production system is the core technology in deep-sea engineering domain.Because of the high-pressure,strong current impact and poor visibility of deep seafloor environment,to achieve accurate docking and reliable sealing by tele-operated connecting equipment is an urgent technological difficulty in deep-sea engineering domain.For the currently shortages of the deep-sea connector such as guiding and docking difficulty,oversized axial preload and insufficient temperature compensation ability,in this paper,subsea accurate docking technology,combined seal technology,sealing structure multi-objective optimization and thermal-structural coupling analysis of the subsea collet connector are studied,influence of temperature loads on the sealing performance of the connector is explored.To ensure the quick and efficient subsea docking,by using planar projection principle,influences of coaxial and angular deviation on subsea accurate docking are analyzed,adaptation of the accurate docking is improved;to improve the adaptability of sealing structure of the subsea collet connector,by analyzing the merit and demerit of metallic seal and rubber seal,a combined seal technical solution is proposed,thrust of the needed hydraulic cylinder is solved;associated parameters of performance of the sealing structure are studied,by using Hertz contact theory and gasket coefficient theory,sealing mechanical properties of lens seal gasket are analyzed,and leakage rate of sphere of the lens seal gasket is described by micro wave crest tangential coefficient,thus a basis for further judgment of sealing performance of the sealing structure is provided.To improve the sealing performance of the subsea collet connector,relations between sealing performance and structure parameters are analyzed,by setting the flange cone and radius of the seal gasket as design variables,setting the axial preload and maximum equivalent stress as the objective function,and setting maximum contact stress as the bound variable,multi-objective optimization model of the subsea collet connector is built,and then optimized by using response surface method;by using finite element analysis(FEA)software,standard sealing structure before optimization and the sealing structure after optimization are numerical simulated,sealing performances before and after optimization under same multiple loading conditions are compared,meanwhile,the sealing performance of the structure under preload condition,working condition and 1.5 times of the rated internal pressure are studied;according to the optimized structural parameters,leakage rate of the sealing structure of the subsea collet connector is solved.According to the problems of heat transfer,convection and thermal radiation of the subsea collet connector,complex heat transfer processes are simplified by equivalent method,thermal conduction model of sea layers between each parts of the connector are built;temperature distribution at rated temperature load of the connector is numerical simulated by using FEA software,steady state temperature distribution and sealing performance of the connector is sought;transient temperature field of the connector is numerical simulated in various working conditions including heating and cooling modes,effect of temperature change on the sealing performance of the connector is analyzed.To obtain the sealing performance changes under the combined influence of external force loads and temperature loads,thermal-structural coupling stress of the connector is analyzed.By using thermal stress function,Fourier law,Lamei formula and coordinate system transformation,three-dimensional stress mathematic models caused by steady state temperature field,transient heat transfer process,internal pressure load and contact are built,theoretical results and simulation results are contrasted and verified by coupling stress calculations of sealing structure;working conditions including pressure raising modes,pressure drawdown modes and pressure shock modes in steady state and transient temperature fields are numerical simulated,in thermal-structural coupling filed,changes of the stress and the sealing performance of the component such as lens seal gasket and flange are analyzed,thus theoretical basis of risk assessment is provided for practical application.In order to verify the correctness of the theoretical analysis and the FEA numerical simulation,prototype experiment of the subsea collet connector is carried out.Equivalent experimental facilities are designed,after 1:1 specimen contrast trial,a better sealing performance of the optimized sealing structure is confirmed;after hydrostatic internal pressure tests of the connector and installation tool,proportional relation between the axial preload and the thrust of loading hydraulic cylinder of the sealing structure is studied;after high pressure tank test,sealing performance of the combined sealing structure is verified;by temperature cycle test,temperature variation,stress variation and packing performance of the structure in raising and cooling modes are tested,the sealing performance of the connector under combined influence of temperature and pressure is studied.Through the prototype marine experiment at depth of 320 m of LuFeng 22-1 a discard oilfield in South China sea,the overall working performance is verified.The developed subsea collet connector with optimized combined sealing structure has better sealing performance and underwater docking ability.The achievements of this study can provide a reference to improve sealing ability and underwater docking efficiency of other subsea connection system,and effectively promote the development of the underwater production system in our country. |
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