Preventive Maintenance Facts

Many companies focus their entire maintenance efforts on a preventive maintenance (PM) program that does not meet the actual reliability needs of the equipment, often because “this is the way we’ve always done it" with no focus on the early detection and mitigation of specific failure modes.

Others use statistical analysis to improve reliability rather than statistical analysis techniques, such as Weibull analysis, to identify assets where reliability is a problem.

Here are some sobering facts that will make you think twice about the effectiveness of a time-based PM program:

1. Less than 11% of asset failures are age related.

How can you identify the frequency of their preventive maintenance activities?

Do you have good data to determine this frequency? If you have, then most asset failures have been correctly documented and coded in the CMMS/EAM [computerized maintenance management system/enterprise asset management].

We find that 98% of companies lack good failure history data.

2. Most reliability studies show that over 80% of asset failures are random. How do you prevent random failure?

In many cases, it is possible to detect early signs of random failure by monitoring the right health indicators. In simple terms, how much has the asset degraded and how long before it no longer functions? This approach allows time to take the corrective action, in a scheduled and proactive manner

3. Let us take this statement a step further.

Preventive maintenance for random failures usually focuses on the health of the asset (through monitoring indicators such as temperature, tolerance, and vibration) to determine where an asset is on the degradation or PF curve (Figure 1.3).

Point P is the first point at which we can detect degradation. Point F, the new definition of failure, is the point at which the asset fails to perform at the required functional level.

The amount of time that elapses between the detection of a potential failure (P) and its deterioration to functional failure (F) is known as the PF interval.

4. A maintenance organization needs to know the PF curve on critical equipment to maintain reliability at the level required to meet the plant’s needs. An example of a potential (partial) failure is a conveyor that is supposed to operate at 200 meters per minute but, because of a problem, can run at only 160 meters per minute. Full functional failure occurs when the conveyor ceases to run.

However, a few barriers prevent a plant from obtaining a higher level of reliability of its assets :

Most maintenance and production departments consider failure only when the equipment is broken. A true failure occurs when an asset no longer meets the function required of it at some known rate of standard.

For example: "if a conveyor is supposed to operate at 200 meters per minute, when the conveyor’s speed no longer meets this requirement, it has failed functionally, causing an immediate loss of revenue for the company"

The maintenance department does not get involved when quality or production rate issues arise in the plant. In most cases, when an asset has failed functionally in a plant, the maintenance department is not informed.

Most maintenance departments do not know the performance targets of the plant equipment and do not understand why it is important that they understand them. This not a failure of the maintenance department but a breakdown in communication of the company’s goals.

Overcoming these barriers is essential to rapid performance in reliability. If an understanding and focus on functional failure is applied by all plant personnel, higher asset reliability will rapidly follow.

5. The focus must be on the alignment of the total plant in meeting performance targets of each asset. These performance targets and current performance rates need to be posted, so everyone is aware if a gap occurs in asset performance. Defining Roles and Responsibilities are critical to success.

The production and maintenance departments must know when an asset no longer meets the performance target. Both departments must accept responsibility for actions to mitigate the performance losses thus Roles and Responsibilities are critical to success of any PM/OpCare Program.

Excepts taken from "Rules of Thumb for Maintenance and Reliability Engineers" by Ricky Smith and Keith Mobley