Defining Preventive Maintenance (PM)
To document and implement PMs effectively, your organization must first agree on one definition of preventive maintenance. We need to define what is or is not included in the scope of process improvement. Many definitions have been developed over time, but IDCON defines it as:
All repetitive actions that prevent a failure or detect a failure early.
Two concepts are covered in this definition. We either 1) prevent a failure from happening, or 2) we detect a failure early.
Figure 1: IDCON's Preventive Maintenance Definition
Failure prevention (left side of image) includes Essential Care. All the actions listed under Essential Care directly impact equipment life — it can be lengthened or shortened depending on how well those PMs are done.
In the center is “FTM” Fixed Time Maintenance. FTM involves changing components or performing PMs on a fixed scheduled based on equipment or component life.
On the right side of the image is Detect Failures. This is where condition monitoring comes in, which includes both objective and subjective inspections.
Now, let’s focus on the word repetitive. When we create a PM program (Document PMs), they should cover actions that both prevent failures and detect failures early. However, It is also important to work on preventive actions that are not repetitive which don’t fit into a regular preventive maintenance program but will still prevent failures.
Let’s take alignment for example.
Alignment is completed upon installation, so it is not a repetitive action. It is not a PM that would be performed again unless vibration analysis indicated a need for realignment. It is vital to do tasks like alignment and balancing right the first time to prevent problems down the line, which is why they are included in the preventive maintenance definition but not part of the repetitive preventive maintenance program.
The Productivity Circle
It must be clear how your PMs fit into your overall work-management process. If it is not clear what the supporting and following systems are, it will be hard to get good results from the PM program. IDCON INC has developed a Reliability and Maintenance Productivity Circle to represent the overall interaction between operations and maintenance. See in the following image where preventive maintenance and condition monitoring activities fit in.
Figure 2: Preventive maintenance and condition monitoring are in orange with a grey box.
You can see that the two parts of PM, preventing failures and detecting them early, are represented in the circle.
Another way we break down the preventive maintenance process is the “chain that cannot be broken.”
Figure 3: PM chain
In the first block, Prevent we have actions such as lubrication, good installation, etc., to prevent failures (and, therefore, work). Then, we move on to objective and subjective inspections, plan and schedule work, and finally, execute the work. This is the basis for successful reliability and maintenance.
It is important to understand that inspections by themselves are useless unless the corrective work is planned, scheduled, and repaired (executed).
Perform a Criticality Analysis
The next step is to determine the right maintenance method for equipment. This is typically done by performing a criticality analysis. A criticality analysis will help define what equipment to focus on first in the improvement process.
I would suggest implementing the critical equipment first. By “implementing” I mean documenting better PMs, executing the PMs for a few months, then planning, scheduling, and executing the repairs. The implementation of PM in a small area of critical equipment will produce fast and sustainable results if it is done right.
Keep scoring simple in your criticality analysis — I suggest five (5) levels max. These can include safety, environmental, high cost, lost production, etc. It depends on what is important to your plant, mill, or mine.
A criticality analysis uses risk x consequence to determine criticality. The risk is the probability of the accident occurring, and the consequence is what would happen in the event the accident occurs. The consequence could be how many hours of downtime a breakdown would cause, for example.
A criticality analysis can be performed in many ways, but we suggest using a block diagram created from a production standpoint:
Plug your equipment into the diagram to determine its criticality from a production standpoint. Multiply the increased cost, or technical side (common failures), times the revenue loss in terms of production loss, and from that, create a simple algorithm between the two determine criticality.
Through the criticality analysis, you've now selected the most important equipment to start with.
Select the Maintenance Method
It is important to know which maintenance method should be used for each component. Therefore, the concept of selecting maintenance methods needs to be part of the process improvement.
There are three options to choose from:
Fixed Time Maintenance (FTM) means performing change-outs or overhauls of equipment on a regular schedule, regardless of condition.
Operating to Breakdown (OTB) is exactly what it sounds like – operating equipment until it breaks down and either repairing or replacing based on cost.
Condition Based Maintenance (CBM) involves monitoring the condition of the equipment and performing maintenance-based anything found during condition monitoring. CBM is often the most cost-effective method, but that is not the case for all equipment.
When the component or equipment has a known Failure Developing Period (FDP), CBM is usually the most cost-effective method. It is typically more expensive to OTB due to additional damage and downtime (but it depends on application). FTM can also be costly because it can result in replacing a component before it is needed, wasting time, parts, and money.
A financial analysis between the three can be used if the most cost-effective option is not obvious. This can sometimes result in a combination of methods being used. The method should be determined equipment by equipment, component by component.
Determine the PM Documentation Process
Agree on a step-by-step process on how to document the PMs for the plant. This process needs to be clearly defined to everyone in the organization (along with training). One reason why it is so important to choose a method is ensure coordination between departments, avoiding duplicate PMs and departments having their own systems.
An option that many try to undertake is Reliability Centered Maintenance (RCM). This is a very detailed process that should be used for extremely critical equipment. Failure Mode and Effects Analysis (FMEA) is a subset of RCM which is also applied to equipment with high criticality. These two methods may be used for 1-5% of equipment in a typical plant.
A good documentation method that can be applied the remaining 95% of equipment and components is IDCON’s Condition Monitoring Standards. Each equipment standard breaks equipment into components, lists symptom modes, instructs out how to prevent failures, and how to find failures early. It also indicates how often the task should be done, which tools are needed to complete the task, and who will perform the task when.
Next Steps
Developing a robust framework for cost-effective preventive maintenance involves defining a clear PM strategy, integrating it into the overall work management process, and prioritizing tasks through criticality analysis. Choosing the right preventive maintenance method depends on equipment specifics and financial considerations. The selection of a documentation process, such as IDCON's Condition Monitoring Standards, ensures clarity and consistency across the organization.
There are more steps to implementing a PM process. The documentation tool develops test routes and PM work orders, assigns and trains personnel, executes PMs and creates a work process. (More about this in coming articles.)
With these foundations in place, organizations can seamlessly apply the chosen methodology, establish test routes, issue work orders, assign responsibilities to effectively execute preventive maintenance plans, thereby fostering reliability, efficiency, and operational excellence.
