Definition:
Maximum Permitted Repair Time (MPRT) is the maximum permitted time to repair a fault after detection. The IEC 61511-1 definition is not specific if this includes time to put back in service, but we should assume it does. Again, here are the four time variables
- a – time to detect the failure
- b – time spent before starting the repair
- c – effective time to repair
- d – time after repair to put back in service.
MTTR = a + b + c + d –> from the failure itself to the restoration
MRT = b + c + d –> meaning MRT does not include time to detect.
MTTR = a + MRT
MPRT < MRT is almost always the case. The reverse are rare cases.
Key Points:
- Critical input for system availability analysis.
- Affects operational downtime.
See Also: MTTR, MRT, MTTR Blog Post
Example:
A plant has a SIF with 2oo3 instruments with diagnostics. They have inventory in stock, technicians are always on call, and the repair is straightforward. The MRT is thus set at 12 hours or a 1.5 shifts. The MPRT is 8 hours as a procedural goal.
Cited Source:
- IEC 61511-1:2016, Clause 3.2.37.3
- Limble article – Guide to Understanding Failure Metrics