PARTIAL-STROKE TESTING OF BLOCK VALVES

Successful implementation of the safety lifecycle model, associated with ANSI/ISA 84.01-1996 (ISA 84) and IEC 61508, hinges on one design constraint---the safety integrity level (SIL). The SIL is a numerical benchmark, related to the probability of failure on demand (PFD). SIL is affected by the design robustness, e.g., device integrity, voting, and common cause faults. It is also affected by the operation and maintenance strategy, e.g., diagnostics and testing interval.