Preventive maintenance (PM)

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What is preventive maintenance (PM)?

Definition

Preventive maintenance (or preventative maintenance) is maintenance that is regularly performed on a piece of equipment to lessen the likelihood of it failing. It is performed while the equipment is still working so that it does not break down unexpectedly. In terms of the complexity of this maintenance strategy, it falls between reactive (or run-to-failure) maintenance and predictive maintenance.

Examples of preventive maintenance

Preventive maintenance can be scheduled on a time or usage based trigger. Let’s look at an example for each.

Time-based preventive maintenance

A typical example of a time-based preventive maintenance trigger is a regular inspection on a critical piece of equipment that would severely impact production in the event of a breakdown.

Usage-based preventive maintenance

Usage-based triggers fire after a certain amount of kilometres, hours, or production cycles. An example of this trigger is a motor-vehicle which might be scheduled for service every 10,000km.

When is it suitable to use preventive maintenance?

Suitable preventive maintenance applications

Assets suitable for preventive maintenance include those that:

  • have a critical operational function
  • have failure modes that can be prevented (and not increased) with regular maintenance
  • have a likelihood of failure that increases with time or use

Unsuitable preventive maintenance applications

Unsuitable applications for preventive maintenance include those that:

  • have random failures that are unrelated to maintenance (such as circuit boards)
  • do not serve a critical function

Preventive maintenance planning

Planning preventive maintenance without the help of CMMS software can be a huge challenge. Since PMs are triggered after a certain amount of time or use, it’s difficult (if not near impossible) to track that data manually, especially if you’re dealing with many pieces of critical equipment. Maintenance software allows you to set PMs according to the triggers that are appropriate for each piece of equipment. Once the trigger occurs, a work order will be created.

Maintenance software also allows organizations to gather data surrounding PM activities to report on or optimize those activities, and set KPIs to work towards.

Advantages of preventive maintenance

Advantages compared with less complex strategies

Planning is the biggest advantage of a preventative maintenance program over less complex strategies. Unplanned, reactive maintenance has many overhead costs that can be avoided during the planning process. The cost of unplanned maintenance includes lost production, higher costs for parts and shipping, as well as time lost responding to emergencies and diagnosing faults while equipment is not working. Unplanned maintenance typically costs three to nine times more than planned maintenance. When maintenance is planned, each of these costs can be reduced. Equipment can be shut down to coincide with production downtime. Prior to the shutdown, any required parts, supplies and personnel can be gathered to minimize the time taken for a repair. These measures decrease the total cost of the maintenance. Safety is also improved because equipment breaks down less often than in less complex strategies.

Advantages compared with more complex strategies

A preventative maintenance program does not require condition-based monitoring. This eliminates the need (and cost) to conduct and interpret condition monitoring data and act on the results of that interpretation. It also eliminates the need to own and use condition monitoring equipment.

Disadvantages of preventive maintenance

Disadvantages compared with less complex strategies

Unlike reactive maintenance, preventive maintenance requires maintenance planning. This requires an investment in time and resources that is not required with less complex maintenance strategies.

Maintenance may occur too often with a preventative maintenance program. Unless, and until the maintenance frequencies are optimized for minimum maintenance, too much or too little preventive maintenance will occur.

Disadvantages compared with more complex strategies

The frequency of preventative maintenance is most likely to be too high. This frequency can be lowered, without sacrificing reliability when condition monitoring and analysis is used. The decrease in maintenance frequency is offset by the additional costs associated with conducting the condition monitoring.

The bottom line

Preventive maintenance, or PM, is regular, planned maintenance that is scheduled according to usage or time-based triggers. The purpose of PM is to lessen the likelihood of equipment breakdowns. There are many instances in which preventive is the best maintenance strategy to use, and it’s much easier to carry out a PM strategy with the help of maintenance software.

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