Structural Strength And Stability Analysis For Deepwater Separator

Subsea separator is the key equipment of subsea oil & gas production system. It has the function of gas- liquid separation / oil- gas-water separation in the bottom of sea, which can reduce wellhead backpressure, enhance hydrocarbon recovery, avoid the formation of hydrate, reduce the produced water discharge and solve the problem of environmental pollution brought by the deepwater oil and gas exploitation, eventually. Hence, it is definitely meaningful to investigate subsea separator under deepwater environment and master a set of deepwater separation technology. Based on the sub-topic of the high pressure alternating load bearing structure analysis and testing technology research originating from the National High-tech R&D Program of C hina(863 Program)- Key techniques of underwater separator research, the analysis of deep water separator bearing structure strength and stability has been conducted. The structure optimization design and analysis has been completed by use of ANSYS software and a 2000m-deepwater deep water separator structure parametric analysis software has been developed. Eventually, a methodology of deepwater separator pressure structural strength and stability analysis has been established. The main research results of this thesis are as follow:(1) Deepwater separator bearing structure strength analysisThe unit division, loading and boundary conditions of numerical model are investigated in detail by using the finite element software ANSYS. A parametric modeling scheme has been proposed, with which an fine design and analysis model of separator pressure shell has been established. With reference to the design method of pressure vessel, the strength analysis of deep water separator based on stress classification method and the strength checking method based on the overall plastic deformation analysis of the direct method have been developed. The application of ANSYS sub-model technique in separator strength analysis has been studied. Meanwhile, the accurate results in the areas of stress concentration area or in key parts have been obtained. The test internal pressure of separator and its bearing structure strength under down pass special conditions has been analyzed. It is proposed that the simulation, analysis and checking of the process of decentralization are conducted by means of the ANSYS transient dynamic analysis.(2) Stability analysis of deepwater separator bearing structureWith reference to the design method of pressure vessel, the nonlinear buckling analysis model of deepwater separator bearing structure has been established. Using the method of subsea separator nonlinear buckling analysis within ANSYS software, the eigenvalue buckling analysis and the instability limit of bearing structure of separator has been investigated. The influence of the ratio of length to diamete r L/D, that of diameter to thickness, hole quantity and thickness, geometric imperfections and ovality on structure critical buckling stress has been studied, which provides reference for stability design of separator bearing structure.(3) The bearing structure optimization design and checking analysis of deepwater separatorBased on optimum structural design of ANSYS, the bearing structure optimization design has been proposed. A three-stage analysis design method, named as “dangerous path stress classification analysis + overall plastic limit analysis + instability limit analysis”, for deepwater separator bearing structure s trength and stability analysis has been adopted, which provides the technical supports for deepwater separator bearing structure optimal design and checking analysis.(4) Deepwater separator parameterization analysis softwareAn parameterization analysis software for deepwater separator bearing structure strength and stability analysis has been developed based on Visual Basic 6.0 language. The software produce all kinds of command flow by use of the principle of parametric modeling of ANSYS, which shorten the complex modeling process and time enormously and boost the calculation efficiency. It provides the strength and stability analysis of deepwater separator bearing structure with effective tools.