SIL-2 Shutdown Loop

[ww2i]

A SIL-2 shutdown loop has experienced several spurious trips. Would you modify proof test intervals or redesign the architecture? How would you decide?

[jeem]

The first step is to understand whether the issue is related to:
Random hardware failures
Systematic/design issues
Proof test induced errors
Process/environmental conditions
Common cause failures
Poor instrument selection or installation
The decision should be based on a structured review. I would be immediately change the proof tests interval or redesign the architecture.

[ivani1]

If reliability data shows the SIL-2 target is already being achieved but availability is suffering, I would generally favor architecture optimization (e.g., voting logic, diagnostics, redundancy) over simply shortening proof test intervals. This approach usually reduces nuisance trips while maintaining the required SIL.

[ww2i]

Explain me what sort of architecture optimization would you apply?

[ivani1]

It can be in the form of sensor voting, redundancy of final element, applying better diagnosis, or segregating process trips from instrument faults.

[ww2i]

So proof test interval should not be the first thing to do rather looking into voting, redundancy should be given a priority?