The Mean Time Between Failures (MTBF) is, together with the MTTR, one of the main indicators of the availability of an asset. The MTBF represents the average time elapsed between two failures in the same asset. The higher the MTBF, the more reliable is the operation of a certain machine — in other words, this machine has a shorter downtime.
How to calculate the MTBF
The calculation of the MTBF is made based on the difference between the total working time and the time lost, divided by the number of failures. The formula is represented by the following expression:
The total working time is the total number of hours in which the machine would have been operating had it not failed; the total breakdown time is the downtime, and the number of breakdowns is the number of failures. Let’s imagine for a second that one asset expected to work 24 hours a day has three stops — once during an hour, another time 2 hours and the last time for 30 minutes.
24 hours would be the total working time and the total breakdown time is 3.5 (1 + 2 + 0.5).
Then, the MTBF will be:
How does MTBF relate to MTTR?
MTBF measures reliability, whereas MTTR is key to understand the efficiency of repairs. Together they allow us to have an estimate of how long a particular system is unavailable. Analysing both MTBF and MTTR lets us predict productivity, which obviously decreases or stops completely during failures. We can also forecast the costs of maintenance and repairs throughout the year.
Based on these indicators, the technical operations manager will know which assets are the least reliable — in other words, which assets need more maintenance or actual replacement. The aim should be to implement preventive maintenance policies, therefore reducing the number of failures. A higher MTBF will make your company more credible and trustworthy, both internally and with your customers. Well done!
As for MTTR, the goal should be to reduce it. On one hand, reducing the MTTR is also dependent on preventive maintenance, given that the number of failures will decrease. On the other hand, it’s also crucial to shorten the repair time. Here, it’s all about acting quickly and preparing your team — the sooner you respond to a failure, the faster it will be resolved.
With a high MTBF and a low MTTR, your system will be working closer to full capacity. In this case, maintain best practices and never fail to invest in preventive maintenance!