The collection of equipment failure data over time allows for proper asset management and life-cycle analysis. From historical equipment failure data, you can assess the reliability of your facility because the data describes how likely it is for each of your assets to fail. Equipment failure indicators refer to measurements of failure rate, mean time to failure (MTTF), and availability. All of these different failure metrics comprise the reliability index, which can be used to drive maintenance strategies.
Failure rate is defined as the number of failures over a certain period of time. Failure rate can alternatively be calculated as the inverse of the mean time between failures (MTBF), where MTBF is the duration of time between occurrences of failure. MTBF is applicable to assets that are repairable – i.e. assets that can be restored to a good working condition after being repaired. For assets that fail beyond economical repair (e.g. consumables), the mean time to failure (MTTF) is a more appropriate metric to use.
Mean Time to Failure (MTTF)
Mean time to failure is a measure of the total time that an asset is utilized before it totally breaks down. MTTF is a useful value to describe the average lifespan of non-repairable assets such as consumables and disposable instruments.
Availability quantifies the amount of time that an asset is able to perform as intended. As opposed to reliability, availability does not necessarily quantify a specific duration of continuous operation. Instead, it measures the total ability of an asset to perform work.
Defining the Reliablity Index
The reliability index refers to the likelihood that a piece of equipment will experience failure over a set period of time. While this value and the criteria to measure reliability might vary across various organizations and industries, it is almost always based on one or a combination of the previously discussed values. By assigning weights to certain performance indicators, a reliability index can be calculated to help identify assets that require special attention, and effectively drive strategies to increase reliability.
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