MTTR Explained: Mean Time To Repair
MTTR measures how quickly you can restore equipment after a failure. Learn how to calculate MTTR, what it reveals about your maintenance operation, and how to reduce it.
What is MTTR?
Mean Time To Repair (MTTR) is the average time it takes to restore equipment to operating condition after a failure. It includes the time from when the failure is reported to when the equipment is returned to service — including diagnosis, spare parts sourcing, the actual repair, testing, and commissioning.
While MTBF measures how often equipment fails (reliability), MTTR measures how quickly you can fix it (maintainability). Together, they determine overall availability:
How to Calculate MTTR
Example: A pump fails 4 times in a year. The repair times are: 3 hours, 6 hours, 2 hours, and 5 hours. Total repair time = 16 hours.
What's Included in MTTR?
MTTR includes the entire downtime from failure to restoration:
- Detection time — time from when the failure occurs to when it's reported
- Diagnosis time — time to identify the cause of the failure
- Spare parts sourcing — time to locate and obtain spare parts
- Repair time — actual hands-on time to fix the equipment
- Testing and commissioning — time to verify the repair and return to service
Typical MTTR Values
| Equipment Type | Typical MTTR |
|---|---|
| Small pump (seal/bearing change) | 2–4 hours |
| Large pump (major overhaul) | 8–24 hours |
| Electric motor (small) | 1–2 hours (swap) |
| Electric motor (large, repair in place) | 8–16 hours |
| Compressor (minor) | 4–8 hours |
| Compressor (major) | 1–3 days |
| Control valve | 1–3 hours |
| Heat exchanger (clean) | 4–8 hours |
| Heat exchanger (retube) | 2–5 days |
How to Reduce MTTR
- Stock critical spare parts: The biggest contributor to MTTR is often waiting for parts. Keep spares for all A-class assets — bearings, seals, impellers, valves.
- Improve diagnosis: Train technicians in troubleshooting. Provide wiring diagrams, P&IDs, and equipment manuals at the point of use.
- Use predictive maintenance: Detecting faults early means you can plan the repair — parts are pre-ordered, the right technician is available, and the shutdown is scheduled.
- Standardise repair procedures: Create standard work instructions for common repairs. This reduces diagnosis time and ensures the repair is done correctly the first time.
- Ensure tool availability: Have the right tools (pullers, bearing heaters, alignment tools) available. Searching for tools wastes time.
- Train operators for early detection: Operators who notice early warning signs (noise, vibration, temperature) report failures sooner, reducing detection time.
MTTR and Availability
The impact of MTTR on availability depends on MTBF:
- If MTBF = 1,000 hours and MTTR = 4 hours: Availability = 1000/1004 = 99.6%
- If MTBF = 1,000 hours and MTTR = 40 hours: Availability = 1000/1040 = 96.2%
- If MTBF = 100 hours and MTTR = 4 hours: Availability = 100/104 = 96.2%
- Key insight: When MTBF is high, MTTR has less impact on availability. When MTBF is low, reducing MTTR is critical.