What Is Mean Time To Failure?
Mean time to failure, often shortened to just MTTF, is a metric used in maintenance to determine the average (mean) time that an asset that cannot be repaired will remain operable before failure. It is similar to mean time between failures, or MTBF, with the only meaningful difference being that MTBF is a KPI applied to assets which can be repaired. In other words, MTTF measures how long until you will have to replace the defective asset whereas MTBF measures how long until you will have to repair the asset and return it to working order.
Calculating Mean Time to Failure
To calculate mean time to failure you need to know the total hours of operation (uptime) and the total number of assets in use. The total hours are divided by the total number of assets. For example, if the total hours of operation are 15,000 and there are 50 assets in total, the equation would look like this:
MTF = Total hours of operation ÷ total number of assets in use
MTTF = 15,000 ÷ 50
MTTF = 300
This specific asset will need to, on average, be replaced after 300 hours. Going one step further, that can be divided by 24 to determine approximately how many days before you will need to consider replacement.
300 ÷ 24 = 12.5
This asset will, on average, last close to two weeks. Knowing the number of hours helps when comparing against past MTTF calculations. Breaking it down to days makes it easier to keep track of when you will need to purchase a replacement and how to factor these purchases into your budget.
Why It Is Useful
Knowing how long, on average, your assets will remain operable are useful for two primary reasons. The first is that MTTF tells you how reliable your assets are, and can be used to identify areas needing improvement. This information helps with decision-making, such as which brands you are going to purchase and how frequently you need to schedule maintenance inspections.
It can also offer indirect insight into how effective your monitoring mechanisms are. Some breakdowns happen as a result of natural wear and tear, but others happen due to negligence and improper use of assets. If your total number of operable hours seems low, no matter which brands you are using or how often they are inspected, the issue might not be with the equipment itself. It could be that whoever is operating them or is responsible for maintaining them might not be performing all of their respective duties correctly.
Other Important Metrics
- MTBF- mean time between failure, the average lifespan of an asset before it must be repaired
- MTTR- mean time to repair/resolve/respond, the average amount of time it takes to take appropriate action after an asset is has failed
- MTTD- mean time discover/discover, the average amount of time it takes to discover an incident after it occurs
MTTF is a crucial piece of data when you are trying to reduce downtime in your facility, and develop a more comprehensive maintenance strategy. Having this approximation available to you works well regardless of which maintenance strategy or combination of strategies your facility implements.
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