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安全仪表系统(SIS)的可靠性是保障安全生产的重要指标,由平均要求时失效概率(PFD(avg))衡量。然而,PFD(avg)计算结果并不能保障SIS在运行阶段的任意时刻均满足目标安全完整性水平(SIL),实时可靠性计算模型PFD(t)可提供更好的分析结果。本文在A.C.Torres-Echeverria等人的研究基础上,对SIS的4个运行阶段建立了实时可靠性计算模型PFD(MooN)(t),并运用MATLAB对该模型进行仿真和分析。最后,通过高完整性压力保护系统(HIPPS)应用实例,得到以下结论:即使PFD(avg SYS)计算结果满足目标SIL,PFD(SYS)(t)也可能在运行阶段的某个时间段内达不到目标SIL;只有当t=TP+RT+n×TI时刻的PFD(SYS)(t)值满足目标SIL时,才能保障SIS在整个运行阶段均能满足目标SIL。该可靠性计算模型的建立,能更好的对SIS进行实时可靠性分析,并为保障SIS在整个运行阶段满足目标SIL提供了有力依据。
The reliability of a safety instrumented system (SIS) is an important indicator of safe production, as measured by the average required failure probability (PFD (avg)). However, the PFD (avg) results do not guarantee that the SIS meets the target safety integrity level (SIL) at any time during the operational phase. The real-time reliability calculation model PFD (t) provides better analysis results. Based on the research of A.C.Torres-Echeverria et al., A real-time reliability calculation model PFD (MooN) (t) is established for the four operation phases of SIS, and the model is simulated and analyzed by MATLAB. Finally, through the HIPPS application example, it is concluded that the PFD (SYS) (t) may reach a certain period of time in the operation phase even if the PFD (avg SYS) calculation results meet the target SIL Can not reach the target SIL; only when the value of PFD (SYS) (t) at the time t = TP + RT + n × TI meets the target SIL, can the SIS be ensured to meet the target SIL throughout the operating phase. The establishment of the reliability calculation model can better real-time reliability analysis of SIS and provide a strong basis for ensuring SIS to meet the target SIL throughout the operation phase.