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Testing of Safety Instrumented System (SIS) Valves... How?

Having gone through the posted article on Safety Life Cycle, I was surprised to see that 50% of SIS faults are from the final control element. That means that 1 in 2 faults can be attributed to issues with the valve assembly and accessories in the safety loop. It is no wonder the latter part of the article focuses on testing of the final control element.

Being in the instrument unit, the method described in the article (testing via the digital valve controller) is the one I am most familiar with and I am curious to know how people in the field, the users, and people familiar with SIS implementation feel about this method.

  • Are there any concerns with this method?
  • Are there different methods where similar actions, Partial Stroke Testing (PST), solenoid valve testing, prevention of spurious trip, etc. are done without degrading the SIL rating?

Below is just a video that contains a demonstration of a PST: