Abstract
In chemical and nuclear power plants, the safety policies have been established according to the consideration of multiple independent protection systems. Independent protection layer 4 (IPL4) is defined as safety instru-mentation system (SIS). Focusing on IPL4, this paper studies the optimal inspection policy and quantitative risk assessment for the SIS with self-diagnosis function. Using Markov models considering dangerous failure (DF) and safe failure (SF), availability A, expected number N(T) of spurious trips caused by SF and probability Q of DF are obtained. Moreover, the risk I caused by SIS failure is analyzed mathematically. We discuss A, N(T), Q and I are influenced by diagnostic coverage and periodic proof test interval. Furthermore, to fulfill the tolerable risk and to consider the inspection cost, the optimal risk-based policy is also discussed. Illustrative examples are given.
