Definition:
Proof Test Interval (TI), also called “Test Interval,” is the maximum allowable time between proof tests for detecting dangerous undetected failures. This is determined when developing the PFDavg calculations for that SIF.
Key Points:
- Shorter TIs reduce average PFD.
- Specified in the Safety Requirements Specification (SRS).
Example:
Proof testing a shutdown valve every 12 months (TI = 1 year).
See also: Proof Test, Proof Test Coverage (Cpt)
Cited Source:
- IEC 61511-1:2016, Clause 11.9.