Definition
Reliability is the probability that an asset or system performs its required function without failure for a specified period, under stated operating conditions. It is a probabilistic property over a time period, distinct from availability, which measures the fraction of time an asset is actually usable regardless of whether a failure has yet occurred.
Key facts
- A probability over a defined time period and stated conditions, not a single point-in-time state.
- Depends heavily on the stated operating conditions; the same asset can have different reliability figures under different load or environment.
- Distinct from availability, which factors in both failure and repair time (how quickly the asset returns to service), not just the probability of not failing.
- Underpins metrics such as MTBF, which express reliability in terms of average time between failures for repairable systems.
What does Reliability reveal about failures?
Reliability measures the probability that an asset will perform its required function without failure over a stated period and under stated operating conditions: a forward-looking probability, not a report of past uptime, though it is typically estimated from historical failure data.
How do teams use Reliability in failure analysis?
Reliability addresses failure-free probability during operation. Availability additionally accounts for how quickly the asset is restored after a failure, combining reliability and maintainability into one usable-time measure. Maintainability specifically addresses how easily and quickly an asset can be restored once it does fail: reliability is about not failing, maintainability is about recovering fast when it does.
FAQ
Frequently asked questions
What does the reliability of an asset in operation mean?
It means the probability that the asset performs its required function without failure over a stated period and under stated operating conditions, distinct from availability, which also factors in how quickly it is restored after a failure.
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