“Maintenance” and “Reliability” terms are frequently mentioned together because there is a strong bond between them, and this bond is so strong that many people don’t differentiate between maintenance and reliability!

Not only this, but also there are some confusions about the roles that maintenance can play towards reliability such as: can maintenance improve and increase the asset’s reliability?

To understand the relation between the two terms, instead of referring to opinions and perceptions we need to refer to the definitions.

Reliability can be defined as: “The probability that an asset or item will perform its required function for a specific period of time under stated conditions”.  Normally measured by Mean Time Between Failures.

Maintenance can be defined as: “The combination of all technical and associated administrative actions intended to retain an item in or restore it to a state in which it can perform its required function”

I’ve illustrated the two definitions in Figure-1 below to show the relation between the two terms.

From the definitions above and Figure-1 below, we can notice that both Maintenance and Reliability are about a common thing, which is enabling the asset/item to perform its required function.
This common thing is the strong bond between maintenance and reliability.

Figure-1: The Relation between Maintenance and Reliability

Reliability is the asset’s ability to perform its required function as stated in another definition:
“Ability of an item to perform a required function under given conditions for a given time interval”

Maintenance objectives are to preserve and protect this ability of the asset/item to perform its required function as stated in another definition of maintenance:
“The sum of activities performed to protect the reliability of the plant”

The asset can be in two states:

1. Performing as designed/desired, in this case proactive maintenance (e.g., PM, PdM, CBM, etc.) is used to keep the asset at this state of designed/desired level of reliability
2. Not performing as designed/desired which means that its reliability has degraded, in this case corrective maintenance is used to improve/increase the asset’s reliability by returning it back to the designed/desired reliability level.

Conclusion:

• Although Maintenance and Reliability are about enabling the asset/item to perform its intended function, they are two different integrating functions.
• The relation between maintenance and reliability is that Maintenance is a reliability tool whereby it keeps its designed/desired level.
• Maintenance can improve/increase the reliability of the asset in case it has degraded by returning it back to the designed/desired level. It’s to be noted that the desired level can’t exceed the designed level.
• Maintenance can’t increase the asset’s reliability level beyond its designed level because it’s inherited from design.
  The only way to increase the asset’s reliability beyond design is by redesign/modification of the asset.
• Maintenance is not only technical work but also the administrative efforts that support the maintenance work
• Maintenance and Reliability are not only equal in importance, but also equal in letters count!