Structure Design And Reliability Study Of Subsea Wellhead Seal Assembly

Subsea wellhead is the key hub equipment during the marine oil and gas development,and the annular sealing assembly is the core components,which is used to cut off the pressure between high pressure wellhead and casing hanger and the pressure in the wellhole,and then form a closed annular space.Subsea wellhead system works under bad conditions,the seal structure and material are required to be high demands with high pressure of oil and gas,strong corrosion,complex operation of installation and long working period.The European and American developed countries are in leading position in the aspects of subsea wellhead system research at present.Therefore,the research of subsea wellhead sealing device structure design and reliability has important significance for developing independent intellectual property rights of domestic subsea wellhead.Firstly,the study of subsea wellhead sealing technology is proposed.The functional and non-functional requirements are studied and the influencing factors are analyzed based on subsea wellhead sealing device working requirements.The overall design is determined with the comparison analysis of subsea wellhead sealing device function structure and scheme.The metal sealing mechanism is carried out.The metal sealing characteristics and the influence factors of metal seal are analyzed,and metal sealing performance evaluation criteria is obtained.Secondly,the subsea wellhead sealing device structure design is studied based on the demand analysis and overall design.Each function module of subsea wellhead sealing device structure design is carried out and the key components finite element analysis is proposed.Sensitivity analysis is carried out aimed at factors affecting sealing performance,and the second order response model of significant factor and contact pressure is obtained.Taking contact pressure and driving load as optimization goal,multi-objective structural optimization design is studied with Ansys software,and the seal body flange radius is optimized.Then,the reliability study of subsea wellhead sealing technology is carried out.The fault tree of subsea wellhead sealing device is established based on fault tree analysis.Qualitative analysis is carried out through the identification of minimum cut sets,and the failure reasons of sealing device are obtained.The repairable Markov model of subsea wellhead sealing device is set up,and quantitative analysis of the sealing technology is carried out.The influence of the transfer rate on the steady-state availability and MTTF.The specific measures of improving sealing performance is proposed.Finally,the experimental simulation prototype is designed based on annular sealing device structure design and optimization design.In accordance with the relevant provisions of API17D and API16A,the finite element analysis and hydrostatic test of simulation prototype are carried out.The feasibility and reliability of sealing device is verified through the analysis of experimental results.The shear test of shear pin is carried out,and the shears can be cut off under the driving load successfully,which can ensure sealing body incentive smoothly.All of the studies provide theoretical and technical support for processing and manufacturing.