Design and Implementation of Functional Safety for Repairable Systems

Abstract

This paper focuses on a practical technique based on IEC 61508 and IEC 61511 standards to design and implement the functional safety for repairable systems. A pilot plant for pressure control under real-world operating conditions is employed as a case study to demonstrate the effectiveness of the proposed design and implementation. The fault trees are utilized to model and analyze the reliability of two sensing elements, two logic solvers, and two final elements used in the designed safety instrumented function (SIF) in terms of probability of failure on demand (PFD). The values of mean time to restore (MTTR) as well as the impacts of proof test effectiveness are considered in reliability modeling of the designed SIF for the case study. Plotting the created PFD equations in MATLAB shows the impacts of perfect and imperfect proof tests during the mission time of the designed SIF. The safety integrity level (SIL) verification shows that the designed SIF can meet the target SIL. The hardware installation for implementing the designed SIF is also described.