I’ve been receiving several inquiries lately regarding the impact of the Partial Valve Stroke Test (PVST) interval on the failure rates of a final element. Specifically asking how does exSILentia® deal with this? exSILentia® allows users to specify if partial stroke testing is performed on their final…
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Entries tagged with: Sil Verification Calculations
- by Iwan van Beurden, CFSE
- Wednesday, March 20, 2013
- Software
Changing the PVST Interval. Hey, my failure rates changed!
- by Dr. Steve Gandy, CFSP
- Tuesday, July 28, 2026
Is Your SIS as Reliable as You Think? The Hidden Risk of “Run-to-Fail”
This is a subject and problem that often comes up when discussing SIS and especially with legacy systems. Given today’s modern instrumentation and the improvements in reliability, some people argue that there’s no need to replace the equipment until it fails. This certainly could be said for Basic Process…
- by Dr. Steve Gandy, CFSP
- Monday, May 11, 2026
- Functional Safety
SIL Verification - Beyond PFDavg / PFH
Have you ever heard people say, “I’ve met the PFDavg target, so I’ve met my SIL target?” It’s true that in low demand we need to meet the PFDavg (or PFH for High/Continuous mode) requirement for the Safety Instrumented Function (SIF) but this is just one of three requirements…