Choosing the right maintenance strategy
Picking the right maintenance strategy depends on the plant's specific needs and priorities. Five maintenance strategies are highlighted.
Maintenance strategy doesn’t enter our non-technical brains unless it directly affects our productivity and well-being. You change the oil in your car’s engine (that’s preventive maintenance) to keep it running so the engine doesn’t seize and you’re not late for work. However, if you’ve ignored your car’s transmission and it drops out on the way to a new business presentation, you have no choice but to stop at a garage for some reactive maintenance. (The other ‘reaction’ will be losing that new business opportunity, but I digress.)
Maintenance professionals who have hundreds of millions of dollars riding on consistent production and on-time delivery know there is much more to the story. The maintenance strategy they choose can have significant financial consequences.
Five methods, various uses
Each of the five basic maintenance strategies — preventive (aka planned), reactive, predictive, condition-based, and reliability based —has its own distinguishing features and optimal applications.
- Preventive maintenance (PM)- This is a maintenance activity that takes place before something breaks so you don’t incur equipment downtime or lost product. It is almost always cheaper to do this than to wait for failure.
- Reactive maintenance- Just as it sounds, this is a maintenance activity that reacts to equipment failure after it occurs. However, sometimes waiting for equipment to fail is the best thing to do, as I’ll explain below.
- Predictive maintenance (PdM)- Maintenance based on specific information about the equipment that is a reliable predictor of imminent failure. Examples include oil analysis, vibration analysis, and thermal analysis.
- Condition-based maintenance (CBM)- This is often used synonymously with predictive maintenance The distinction? CBM is driven from real-time data gathered from sensors and other devices that measure specific conditions against known parameters of failure so that action can be taken in advance.
- Reliability-centered maintenance (RCM)- has a much broader scope, often incorporating all of the other strategies. RCM has been referred to as a process to establish the safe minimum levels of maintenance. RCM begins by answering seven questions about the equipment:
- What are the functions and associated performance standards of the asset in its present operating context?
- In what ways does it fail to fulfill its functions?
- What causes each functional failure?
- What happens when each failure occurs?
- In what way does each failure matter?
- What can be done to prevent each failure?
- What should be done if a suitable preventive task cannot be found?
RCM is a complete engineering approach designed to do whatever it takes to promote the greatest level of equipment reliability with the least investment of maintenance cost.
Five guidelines for choosing a maintenance strategy:
Preventive maintenance (PM)- You’ll need to develop detailed job plans that spell out the maintenance tasks and the time intervals for each to keep the equipment up and running. You also should have the means to capture the conditions found at each inspection. This is usually done with a PM work order and captured by the computerized maintenance management system (CMMS) for later analysis.
Reactive maintenance (RM)- It only works if the equipment cannot be easily / cheaply repaired. If it is cheaper to replace than to repair, use reactive maintenance and then make sure you have a ready supply available. A common example is an electric motor rated at 5hp or less.
Predictive maintenance (PdM )- Requires an investment either in analytical equipment and user training or contractors to do the analysis. The decision depends on your specific situation.
Condition-based maintenance (CBM) – Considered a good strategy overall (again, depending on your type of equipment) but it is also a good way to minimize energy expenditure. CBM usually requires an investment in a remote data gathering system and user training.
Reliability-centered maintenance (RCM)- A great maintenance strategy and considered the most cost-effective overall. As we mentioned, RCM may encompass all of the other strategies depending on the equipment component and the available resources.