Research On Reliability Assessment Method Of Subsea Blowout Preventer Systems For Offshore Oil

Under the condition of abundant offshore oil and gas resources,the exploration of offshore oil and gas will become one of the important directions for the development of national oil and gas.Subsea blowout preventer(BOP)is the most critical safety equipment during offshore oil and gas drilling.Subsea BOP can be used to control the wellhead pressure when the blowout occurs and close the wellhead in time in emergencies such as typhoons.With the increasing water depth of equipment operation,more and more attention should be paid to its reliability.The reliability assessment of subsea BOP can identify the dangerous factors and weak links that affects its normal operation and provide a reference for the development,risk control,manufacturing improvement and reliability design of the subsea BOP.According to the different characteristics of the hydraulic control system,electronic control system and structure system of subsea BOP,this paper proposes three different system reliability assessment methods.Based on dynamic Bayesian networks(DBNs),a reliability assessment of the hydraulic control system for subsea BOP considering the influence of component correlation is proposed.Based on dynamic DBNs,a reliability assessment method of the electronic control systems for subsea BOP considering the influence of component correlation,common-cause failures,and incomplete coverage is proposed.And based on finite element analysis,stress-strength interference model and Monte Carlo method,a structural reliability assessment method of subsea BOP is proposed.The above methods can solve the problem of difficulty in modeling multi-state degraded systems under the influence of strong coupling between components.The hydraulic control system of subsea BOP is the key component of the control system.In the operation process,when a certain function is performed,different hydraulic components will act in succession.There are multiple failure and degradation states for hydraulic components.Once the performance of a key component in the hydraulic system is degraded,it will have a correlation effect due to the coupling between the components,which will accelerate the degradation rate of the entire system.In order to solve the modeling problem of multi-state degraded system under the influence of strong coupling between components,a reliability assessment method of the hydraulic control system of subsea BOP based on DBN considering the influence of component correlation is proposed.By observing system parameters,the current performance status of the component can be identified,and its impact on other components can also be determined.According to the influence of component correlation,the performance degradation of other components can be calculated,and the DBN model of the hydraulic control system of subsea BOP can be established.Finally,the change law of system reliability and availability under different maintenance strategies and different component correlation coefficients can be obtained.The electronic control system of subsea BOP is a typical fault-tolerant multiple redundant system.Due to the greater impact of common cause failures,the advantages of fault-tolerant multiple redundant systems are severely reduced.At the same time,the system also has mutual influences between components.In order to solve the the problem of difficulty in modeling multi-redundant system under the influence of strong coupling of components,a reliability assessment method of the electronic control system of subsea BOP under the influence of component correlation,common-cause failure,and incomplete coverage based on DBN is proposed.First establish the structural model of the DBN through the functional connection and influence relationship between the various components of the system,and then establish the parameter model of the DBN through historical data and expert experience.Finally,the change law of system reliability and availability under different maintenance strategies,different component correlation coefficients,and different configurations can be obtained.The mechanical system is an important execution unit of subsea BOP system.The performance degradation and failure of structural systems are usually related to changes in fatigue mechanical properties,and its working load has the characteristics of dynamic changes.In order to solve the problem of lack of data in the reliability assessment of mechanical systems,a mechanical srructure reliability assessment method of subsea BOP is proposed which is based on finite element analysis,stress-strength interference model and Monte Carlo method.The equivalent stress data required for reliability assessment can be obtained through finite element analysis.According to the S-N curve,the stress-strength interference model and the Monte Carlo method,the failure rate of the structure can be obtained,and the reliability of the mechanical structure can also be obtained.Finally,fatigue analysis can be performed on structural parts.