Measuring the spread between corrective and preventive maintenance

An effective preventive maintenance program should find issues before they morph into problems, and tracking it all carefully will help you know if your building’s operations are headed off track or if they’re staying true to best practices.

Preventive maintenance (PM) is an action carried out in a programmed manner to keep equipment in the desired functioning state. Another objective of PM is to detect corrective maintenance action to be taken to prevent an emergency or a non-productive situation. Life Cycle Engineering explores the difference between CM and PM.

Corrective Maintenance (CM) is an action where a repair or adjustment is carried out to solve a condition detected during the PM process due to the fact that the correction was beyond the allocated time or resources of the PM.

It can be said that the efficiency of the preventive maintenance program largely dictates the extent of the work required for CM, and is a vital aspect of an efficient maintenance program in a facility. Establishing a PM program alone doesn’t ensure efficient maintenance in a facility; some other factors also have to be considered –

Frequency of the preventive maintenance program

Implementing a PM program based on the manufacturer suggested interval is a good starting point but that cannot be the benchmark. This routine requires adjustment, based on the operation history of the equipment.

The frequency of a PM in a facility should be based on ‘Mean time between failure’ (MTBF). This permits to calculate a realistic time frame in which checking the equipment, can lead to identification of potential problem. Effectively fixing these problems through CM extends the MTBF of the equipment.

Efficiency of the preventive maintenance program

The short and simple way to describe the efficiency of a PM is that ‘an effective PM program should find problems’. But this doesn’t imply that overwhelming the maintenance department with PM is going to ensure the most efficient system. Many a times there are so many PM to carry out that there is very little time for CM or even emergencies. The effectiveness of a PM program actually rests on the ratio of PM to CM, and this ratio depends on quite a few variables:

  • Impact of the equipment failure on production and safety.
  • The age of the equipment.
  • The history of the equipment.
  • The technology used in the equipment.
  • The desired productivity of the equipment.
  • The amount of resources available.

Working through all these factors, if the ratio of preventive maintenance to corrective is approximately 6:1 (for 6 PM there is 1CM) the preventive maintenance program can be called reliable. This is a proven theory and holds good for many facilities though it cannot be steadfastly held for all PM and for all processes.

The proper ratio of PM to CM should be determined only after a detailed analysis of past performance and PM work order history and cannot remain as a guess work. Excellence in maintenance can only come from a dedicated proactive approach and applying proven processes.


Resources | Analyzing the Relationship of Preventive Maintenance to Corrective Maintenance

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