Predictive vs. Preventive Maintenance
Though both methodologies work to extend the life of assets, prevent unexpected breakdowns and save organisations money, Preventive Maintenance (PM) and Predictive Maintenance (PdM) are very different approaches. The key to the most effective asset management is understanding the difference between preventive and predictive maintenance, and learning to employ the right balance of each within your maintenance strategy.
Preventive Maintenance is performed while the equipment is under normal operation to avoid unexpected breakdowns and the associated downtime and costs. During the specified date and time, equipment is shut down and PM tasks on that piece of equipment are performed. Maintenance is set on a schedule based on calendar dates or usage, often at the recommendation of the manufacturer. For example, most forklift manufacturers suggest performing preventive maintenance every 150 to 200 hours of operation. Performing this maintenance can mean extending the life of assets, increasing productivity, improving overall efficiency, and reducing maintenance costs.
Challenges of Preventive Maintenance
Preventive Maintenance is based on the theoretical rate of failure, and does not account for actual equipment performance. Every organisation is different and daily operations impact equipment functionality, so utilising this strategy can result in performing unnecessary maintenance. Maintenance requires availability for specific parts and labour, and for certain pieces of equipment, a significant amount of time allocated for cool down and ramp up. All of this increases downtime for equipment that might not necessarily require maintenance in the first place. This activity can also introduce collateral damage, resulting in more unexpected failures.
Predictive Maintenance, on the other hand, directly monitors equipment performance during normal operation to anticipate failure. So, instead of scheduling maintenance on electric motors at 150 to 200 hours of operation regardless of performance, organisations monitor and test conditions such as lubrication, vibration and noise corrosion on a consistent basis. For example, taking vibration measurements on an electric engine at recommended intervals will more accurately detect bearing wear, and allows organisations to take proactive, cost-effective action such as replacing a bearing before total failure occurs.
Your Computerised Maintenance Management System (CMMS) can also integrate with your equipment monitoring devices to help drive maintenance schedules, and empower organisations to import readings based on equipment condition, graph results and automatically trigger an email or generate a work order when acceptable boundaries are exceeded.
P-F Curve and the Predictive Maintenance Advantage
The P-F Curve is a useful way to illustrate equipment behavior and the process of functional failure. The key to efficient maintenance is maximising the P-F Interval, or the time between when an organisation can discover a piece of equipment is failing and when it actually fails.
The P-F Interval ranges from days to a few weeks or months. Condition monitoring practices maximise the P-F Interval because it can efficiently extend the window before functional failure. PdM also has fewer disruptions than the shutdown process required by Preventive Maintenance.
Challenges of Predictive Maintenance
PdM is more complex to establish than a PM schedule, and usually requires the need to own and use condition monitoring equipment. Employees must undergo training to use the equipment and accurately interpret the data they discover.
There are also providers who will perform condition monitoring tasks and analyse the results for your organisation. eMaint’s CMMS can integrate with SEMEQ and others to streamline the process. For example, SEMEQ offers Equipment Monitoring Services, Lubrication Engineering and Reliability Engineering. When a negative diagnostic report is recorded by SEMEQ, eMaint can automatically generate a corrective work order.
Combining the Power of PM & PdM
Leveraging the benefits of both Preventive and Predictive Maintenance makes for the best maintenance programmes. Use each method where applicable, and decide which strategy to apply based on disruption due to equipment downtime, the P-F Interval, cost of parts and labour time, and equipment history.
CMMS solutions such as eMaint can help maximise the power of these maintenance strategies by tracking and scheduling PM and PdM, and integrating with condition monitoring equipment to enable corrective action.
For further information on the difference between Preventive and Predictive Maintenance, check out eMaint’s Best Practice Webinar, “From Preventive to Predictive: A PdM Primer.”
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