I don’t really think there’s a golden ratio for how many PMs you have for each corrective repair task. Here’s why.
You might have heard of the 6:1 rule. The gist of this rule is that for every six preventive maintenance tasks you do, you should find one corrective task. If you end up doing more PMs for each corrective task, you’re doing too much PM. If you have more corrective tasks, you’re doing too little.
It seems like a decent idea, and there is some good research to back it up, but technology has developed a bit since that research was done. These days, we have other ways of tracking asset health that give us more precision and insight than before.
With that in mind, I’d say it’s more important to know each asset’s history and make decisions based on that data. For instance, you might look at these metrics:
- Replacement parts purchased
- Amount of asset downtime
- Time to complete preventive maintenance tasks
- Time to complete reactive work orders
- Potential impact of asset failures on core operations
- Frequency of each type of maintenance work done
- When failures tend to occur
If an asset isn’t central to your operations, frequent PM may not be the best option. On the other hand, if a certain failure would cause an expensive interruption to your core processes, you’ll want to make sure that failure doesn’t happen. In that case, more frequent PM—and of the right type—would be necessary.
With this kind of information, finding whether the number of PM tasks fits a certain ratio doesn’t really make sense. More important is how effective your PM is at preventing costly failures and whether those failures would result in significant losses.
For example, if you discover that one of your assets keeps failing in the same way over and over in spite of frequent PM, you might be doing too much of the wrong thing. It’s not that the ratio of PM to CM is off—it’s that what you’re currently doing isn’t working. Find what you need to change to make your preventative maintenance more effective, and you should start to see improvement.
In the end, the key here isn’t doing more or less PM. It’s about using it in ways that work best for your operations.