What is reliability?

What is reliability?

We’ve talked around it before. Last year, we defined reliability culture as “the overall cultural shift that’s required for an organization to fully understand the big picture when it comes to asset reliability.”

More recently, we talked about the difference between maintenance and reliability, noting that reliability is a much more holistic, long-term approach to asset management than maintenance. But what exactly is reliability, and why is it important to understand the difference between it and other maintenance-related concepts?

Fiix Solutions Engineer Stuart Fergusson remembers a boss he had at a former job describing reliability like this: “What is darkness? It’s the absence of light. You can think of reliability the same way. It’s the absence of unplanned downtime.”

In its simplest terms, this definition makes perfect sense. If a piece of equipment is breaking down unexpectedly, it’s not reliable. Elsewhere, the concept has been defined as “the probability that a component or system will perform a required function for a given time when used under stated operating conditions.”

Essentially, these two definitions are saying the same thing. A reliable piece of equipment performs like it’s supposed to every time you use it.

Reliability vs. availability

Before we dive deeper into what reliability is, let’s take a quick moment to clarify what it isn’t.

People often confuse reliability and availability or use the two terms interchangeably. Weibull.com defines availability as “the probability that a system is not failed or undergoing a repair action when it needs to be used.”

The key part of this statement is “when it needs to be used.” As we discussed, a piece of equipment is reliable when it avoids unplanned downtime. That same piece of equipment could be 80% available but still 100% reliable, because that 20% downtime was planned in advance to keep everything running smoothly. Since availability does account for repairs and repair time, it’s really just a function of reliability.

The evolution of maintenance and reliability

Over time, experts have come to understand that design, operation, technology, and organizational culture all significantly impact reliability. In short, the concept encompasses so much more than maintenance, which is why the distance between reliability and traditional maintenance practices has grown over the years.

How did we come to this modern understanding of reliability? According to Lifetime Reliability, the concept can be traced back to the 1960s. Prior to this time, it was assumed that the longer a piece of equipment was running, the more likely it was to fail. But a study in the aviation industry revealed that only 11% of failures could be linked to an asset’s age. This brought about a huge change in the way people thought about equipment failure. If 89% of failures were occurring for reasons other than the equipment simply being old, what were those reasons?

So began the idea of condition-based maintenance, wherein failures were linked to a change in the condition of an asset, rather than its age. In order to carry out the analysis this concept required, root cause analyses had to be carried out to try to understand where the problem occurred that caused machinery to fail.

Reliability-centered maintenance

While condition-based maintenance introduced a new dimension to asset management, it was still only based on whatever a machine’s current condition was. In recent years, reliability-centered maintenance has gained popularity. This concept focuses on making maintenance decisions based on maximizing overall machine reliability over a period of time. Since, as we established earlier, reliability takes everything from design to organizational culture into consideration, there can be many different frameworks incorporated into a reliability-based maintenance approach.

Reliability-centered maintenance should not be thought of as an alternative to any one maintenance strategy. Rather, if carried out properly, a reliability-based approach will take many methods into account, depending on what increases reliability for any one asset.

Let’s take a car for example. If you were to use a reliability-based approach to caring for it, you would use a time-based preventive maintenance schedule for an oil change, a condition-based approach for your tires, and a run-to-fail approach for light bulbs.

The bottom line

When all is said and done, reliability encompasses all the insight that’s been gained with regards to maintenance practices over the years. With advances in technology, productivity, design, and data processing capabilities, it only makes sense that our approach to asset management takes on a more holistic approach as we learn more. In other words, reliability is a concept that will keep us out of the dark if we think about it in the right way.