6.0. Final Control Elements for Safety Instrumented Systems

During SIS design, all constituents for each SIF must be addressed especially final elements. According to the published reports, final elements account for nearly 50% of SIS failure. Final control elements consist of control or shutdown valves/damper, actuator, and associated accessories such as solenoid valve, positioner, etc. As final control elements are the weakest link in SIF, hence SIS, therefore, final elements and associated devices must be selected with proper care so as to improve the reliability, availability, and reduce risks of the associated SIF.
A dangerous condition is sensed by process transmitters to initiate the logic solver. Based on a response from the logic solver, ...

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