Within practically all computerized maintenance management systems (CMMS), there are mechanisms to do preventive maintenance (PMs). These PMs are in place to direct an action to perform predetermined tasks or a list of tasks on an asset. They can be as simple as inspections, lubrication, or replacement of an asset before failure. Anyone within a reliability or asset management functionality should be intimately familiar with PMs and their programs. But what happens when you cancel a PM in your CMMS? Well, it depends.
Static PMs
There are generally two types of mechanism types that generate a PM. The first mechanism is static. This type of mechanism creates a PM regardless of the status of the previous PM being completed or canceled. Think of these as your regulatory PMs. PMs such as inspecting pressure relief valves annually to satisfy a local code would be an annual static PM that is targetted not to exceed. Depending on the lead time to create the PM, the mechanism will make the due date of the PM at the set time interval. As a static PM, you could have many of the same PMs in your open backlog simultaneously if you failed to complete or cancel one.
Dynamic PMs
The other type of PM is a dynamic PM that gets created and has a targeted completion date based on the status change date of the previously due PM. If the dynamic PM is set at a 30-day frequency, the CMMS makes the PM’s due date 30 days after the status date of the previous PM's when it was canceled or completed. If a monthly PM is completed thirty days late, the next PM is due 30 days from that completion date no matter what the previous PM's original due date was. In this example, you may have gotten the monthly PM done only two times over three months. As a dynamic PM, there will only be one active PM in the open backlog.
PM compliance per SMRP 5.4.10 Preventive Maintenance (PM) & Predictive Maintenance (PdM) Work Order Compliance
In an earlier blog, we explored the completion of PMs and how PM compliance is measured per SMRP 5.4.10 Preventive Maintenance (PM) & Predictive Maintenance (PdM) Work Order Compliance. But what happens when you cancel the PM? Regardless if the mechanism for the PM is static or dynamic, the canceled PM impacts your SMRP 5.4.10. However, depending on whether it is static or dynamic, the significance of the impact differs.
Reference - SMRP 5.4.10 Preventive Maintenance (PM) & Predictive Maintenance (PdM) Work Order Compliance refers to the 10% rule that looks to see if the PM was completed +/- 10 of the frequency interval.
Work Order | Due date | Status | Status Date | SMRP 5.4.10 | Comp. (YTD) |
1 | 1/31 | Complete | 1/31 | Compliant | 100% |
2 | 3/2 | Complete | 3/31 | Non-comp. | 50% |
3 | 4/30 | Canceled | 4/30 | Non-comp. | 33% |
4 | 5/30 | Complete | 5/3 | Non-comp. | 25% |
5 | 6/2 | Complete | 6/28 | Non-comp. | 20% |
6 | 7/28 | Canceled | 6/28 | Non-comp. | 17% |
7 | 7/28 | Complete | 7/30 | Compliant | 29% |
8 | 8/29 | Canceled | 8/30 | Non-comp. | 25% |
9 | 9/29 | Complete | 9/30 | Compliant | 33% |
10 | 10/30 | Complete | 10/30 | Compliant | 40% |
11 | 11/29 | Complete | 11/30 | Compliant | 45% |
12 | 12/30 | Complete | 12/30 | Compliant | 50% |
Example 1 - Dynamic PM, first one due on 1/31, on a 30-day interval, lead time to create PM 30 days before it is due
Work Order | Due date | Status | Status Date | SMRP 5.4.10 | Comp. (YTD) |
1 | 1/31 | Complete | 1/31 | Compliant | 100% |
2 | 3/2 | Complete | 3/31 | Non-comp. | 50% |
3 | 4/1 | Canceled | 4/30 | Non-comp. | 33% |
4 | 5/1 | Complete | 5/3 | Compliant | 50% |
5 | 5/31 | Complete | 6/28 | Non-comp. | 40% |
6 | 6/30 | Canceled | 6/28 | Non-comp. | 33% |
7 | 7/30 | Complete | 7/30 | Compliant | 43% |
8 | 8/29 | Canceled | 8/30 | Non-comp. | 38% |
9 | 9/28 | Complete | 9/30 | Compliant | 44% |
10 | 10/28 | Complete | 10/30 | Compliant | 50% |
11 | 11/27 | Complete | 11/30 | Compliant | 55% |
12 | 12/27 | Complete | 12/30 | Compliant | 58% |
Example 2 - Static PM, first one due on 1/31, on a 30-day interval, lead time to create PM 30 days before it is due
In both examples, we completed the same amount of work in the year, but we have two different SMRP 5.4.10. The dynamic PM’s compliance finished the year at 50%, whereas the static PM's compliance finished at 58%.
In the static case, the fourth PM was due on 5/1 and completed on 5/3. Therefore, this PM was compliant because we are within the +/-10% interval. But in the dynamic case, the PM was due on 5/30 and completed early, thus non-compliant.
Cautions with canceling PMs per the type of PM
There are a variety of cautions with this approach. First, if the lead time to generate at PM is significantly less, it is less likely that you will do the PM early because it is not in your Open Backlog yet. The second caution is that if you skip the PM for more than 2X the interval, the number of completed PMs could be misleading. Another caution is that with the static PM approach, you could have more than one PM in your open backlog at a time, and it could complicate which PM to complete.
The objective of this exercise is to acknowledge that can be influenced by whether the PM is static or dynamic when canceling a PM. This also shows that there are times when the PM has a dynamic mechanism and times when the PM should be static. Regardless of how the PM is generated, understanding what PM Compliance means when canceling a PM should be deeply understood.