Research On Safety Integrity Levels Evaluation Method Of Safety Instrumented Systems For Offshore Oil

Safety instrumented systems can monitor the state of the equipment,take safety instrumented function to prevent dangerous accidents caused personal,equipment and environment injury or to reduce the loss caused by dangerous accidents when equipment fails dangerously.A safety instrumented systems can perform one or more safety instrumented functions.Within the prescribed time and condition,the probability that a safety instrumented systems performs its safety instrumented function known as the safety integrity level(SIL).Through testing and evaluating the safety instrumented systems,it can be determined whether the equipment designed and installed meets the safety requirements,which plays an important role in ensuring the safe and stable operation of process industrial equipment.This paper proposed a multi-stage dynamic Bayesian network(MDBN)method for safety instrumented systems SIL determination.Modeling and analysis are carried out according to the characteristics of different redundant structures and failure characteristics in safety life cycle of safety instrumented systems.The problems of SIL evaluation under the influence of parameter uncertainty,modeling evaluation of heterogeneous redundant structures,and SIL evaluation and parameter optimization under consideration of inspection,testing and maintenance optimization are solved.There are many uncertain factors such as the structural uncertainty and parameters uncertainty in the process of SIL evaluating of the safety instrumented systems.These factors will lead to produce huge deviation,which will seriously affect the accuracy of the evaluation results.In order to solve the problems of difficult SIL evaluation and poor accuracy of results under the influence of parameter uncertainty,an evaluation method for safety instrumented system based on MDBN and Monte Carlo simulation is proposed.A general SIL evaluation model was established for multi-redundant unit system with different redundant structures in safety instrumented systems.Based on DBN model of proof test interval stage and test interval stage,the automatic modeling method of conditional probability between nodes in each stage was put forward.The automatic modeling of conditional probability between nodes of MDBN model is realized.The process of SIL evaluation under the influence of parameter uncertainty is established.The method using expert evaluation and Monte Carlo simulation preliminarily determine the scope of the prior probability,and combined with MDBN model to evaluating system SIL under the influence of parameter uncertainty.The heterogeneous redundant structure of safety instrumented systems can greatly reduce the common cause failure probability increase caused by redundant configuration.The evaluation and analysis of the heterogeneous redundant structure can help designers and staff to determine the selection and configuration of the heterogeneous redundant structure.However,there is no strict standard and mathematical model for evaluation of heterogeneous redundant structure,and it is difficult to determine the evaluation parameters,establish the evaluation model and configure the redundant structure.A new SIL evaluation method for heterogeneous redundant structure is proposed,which combines the heterogeneous redundant common cause failure βmodel and MDBN.The influence of common cause weight ω and β factor on common cause failure is investigated.According to the structure and parameter characteristics of the equipment,the common cause failure β is modified.Combined with the modified β,a general MDBN model was constructed.The SIL evaluation of heteromorphous redundant structures is realized.In order to solve the problem that heterogeneous redundant equipment is difficult to configure,a method of life cycle cost calculation for safety instrumented systems based on system evaluation results is presented.Integrate the result of system evaluation with cost calculation,the cost analysis of heterogeneous redundant structure is realized.The results provide a basis for configuration optimization of heterogeneous redundant structure.In the process of design and evaluation of safety instrumented systems,the choice of proof test strategy and maintenance strategy plays a vital role.However,most of the existing evaluation methods are proposed for the maintenance combination of periodic proof test and preventive maintenance,and there are problems that it is difficult to evaluate the combination of special maintenance strategy,and it is difficult to select the maintenance strategy and maintenance parameters.In order to solve the problem of SIL evaluation considering special proof test and maintenance conditions,established an MDBN model for SIL determination of safety instrumented systems integrating proof test and maintenance processes.It realized the evaluation of the unavailability and SIL of the system under the combination of different proof test and maintenance strategies.In order to solve the problem of proof test and maintenance strategy and parameter optimization,this paper completed the formula for calculating the safety life cycle cost of safety instrumented systems that integrates maintenance costs.It built a maintenance strategy optimization model based on the SIL evaluation results of the safety instrumented system and the system cost.This method takes the cost of the safety instrumented system as the optimization goal,and takes the SIL in the entire operating cycle as the constraint condition,and realizes the optimization of the proof test and maintenance strategy and parameters of the safety instrumented system.