化工装置安全仪表系统安全完整性等级计算

摘要

Safety instrumented system(SIS)is an important guarantee for ensuring the safe operation of chemical plants.How to calculate the safety integrity level(SIL)of safety instrumented system is an urgent issue in engineering design.Combining IEC 61508 and IEC 61511,the SIL of the safety instrumented system is calculated from the hardware structure mandatory requirements and the loop failure rate on demand.The mandatory hardware structure requires the calculation of the safety failure rate of each subsystem.The SIL of each subsystem is determined according to the safety failure rate.The SIL of the entire circuit is taken as the lowest value among all subsystems.In addition,according to the different voting structures of the loop,the failure rate on demand of the entire loop is calculated,and the SIL of the loop is determined according to the demand failure efficiency.Take the lowest of the two calculation results as the final SIL of the loop.Finally,with a temperature monitoring safety interlock circuit as example,the safety integrity level of the entire loop is calculated quantitatively,and some suggestions on how to improve SIL of the loop are provided,which provide important reference for designers of safety instrumented systems.%安全仪表系统是确保化工装置安全运行的重要保证.如何计算安全仪表系统的安全完整性等级是工程设计中急需解决的问题.结合IEC 61508和IEC 61511,从硬件结构强制要求和回路需求失效率两个方面,对安全仪表系统的安全完整性等级进行计算.硬件结构强制要求计算每个子系统的安全失效率.根据安全失效率确定每个子系统的安全完整性等级,整个回路的安全完整性等级取所有子系统的最低值.另外,根据回路不同的投票结构,计算整个回路的需求失效率;根据需求失效率确定回路的安全完整性等级.取两种计算结果的最低值作为回路最终的安全完整性等级.最后以一个温度监控安全联锁回路实例,对整个回路安全完整性等级进行定量计算,并提出了一些改善回路安全完整性等级的建议,为安全仪表系统的设计者提供了重要参考.