In brief
Equipment availability is the proportion of planned time during which a plant is actually ready for operation and able to perform its required function.
Contents
What is Equipment availability?
Equipment availability is a key metric in production and maintenance. It shows how much unplanned and planned downtime reduces the usable time of a machine or line. Different definitions are used depending on the purpose, which is why figures from different companies are only comparable if the basis of calculation is known.
Technical or inherent availability is calculated from MTBF and MTTR: MTBF divided by the sum of MTBF and MTTR. Operational availability additionally takes account of waiting times, for example for personnel or spare parts, and planned maintenance. In the OEE metric, availability is the factor actual running time divided by planned production time. Example: 400 hours of running time out of 440 planned hours gives around 91 per cent.
Availability increases when failures become less frequent or are remedied more quickly. Preventive and condition-based maintenance extend the time between failures, while well-thought-out spare parts stockholding shortens downtime. Particularly for bottleneck plants, the availability of critical components often determines the entire output.
In practice: maintenance and procurement
To make improvements, it helps to classify downtime by cause, for example fault, waiting for material, changeover and maintenance. If waiting times for spare parts account for a noticeable share, an analysis of critical parts with a stockholding decision is usually the quickest lever.
Synonyms and abbreviations: technical availability · machine availability · plant availability · asset availability
Frequently asked questions
How is equipment availability calculated?
A widely used formula is: availability equals actual running time divided by planned production time. Alternatively, technical availability is calculated as MTBF divided by the sum of MTBF and MTTR. If, for example, MTBF is 190 hours and MTTR is 10 hours, the technical availability is 95 per cent.
What is the difference between availability and OEE?
Availability only records how long a plant actually runs. OEE, overall equipment effectiveness, additionally multiplies availability by the performance rate and the quality rate. A plant can therefore be highly available and still have a low OEE if it runs slowly or produces a lot of scrap.
How can equipment availability be increased?
Starting points are fewer failures through preventive and condition-based maintenance and shorter downtime through rapid diagnosis and well-organised spare parts supply. Changeover times and planned maintenance can often be shortened too. Which lever achieves the most is shown by an evaluation of downtime by duration and cause.
Does planned maintenance count as unavailability?
That depends on the definition. In OEE analysis, planned maintenance is often booked outside planned production time and then does not reduce availability. In operational availability, by contrast, it is frequently included. It is important to define the rule consistently so that the figures remain comparable over time.