What is Reliability? What is the Definition of Reliability? There are 4 Ways to Define Reliability

What is Reliability? How is Reliability Defined? We’ve Got Four Definitions of Reliability.

Reliability is a probability. It is a measure of the chance of delivering a required outcome.


Slide 15 – What is Reliability? Define Reliability? Four Separate Definitions of Reliability are Listed and Explained When They Apply.


What is reliability? The formal definition of reliability is, “The probability that an item of plant will perform its duty without failure over a designated time.” In this reliability definition, reliability is measured in units of time, or throughput, or by some other measure of service life, or operational performance.

In the military, reliability has a different definition. It is the chance of completing the mission. The mission is to successfully neutralize or eliminate a target. The measure is one of success. Time is not a factor. The mission may take half an hour for a fighter jet to hit its target and return, or it may take half a week for an army unit to capture an enemy outpost, or it may take half a year for a naval fleet to subdue an enemy naval Flotilla. In the military, all that matters is the mission is successful.

At Lifetime Reliability Solutions Consultants we have a different definition for reliability. It is viewed as the chance of success, where success is defined by any result you want to achieve. This permits reliability, i.e. the chance of success, to be used as a measure for every situation. Once a situation is defined as a required outcome then reliability measures the chance that the outcome will be delivered.

The racing car shown in the slide above will never go down an off-road, boulder-strewn track that the four-wheel drive car can navigate easily. The off-road vehicle will never win a race against the racing car on a grandprix track. The racer is 100% unreliable on a rocky bush track, and the off-road car is 100% unreliable on the race track. Each is specifically designed, built and run for events they can win—if used in the wrong circumstances, they cannot be successful.

Reliability is a creation. Reliability is a result. We create our own success. A company creates its own successes. Success is can be reduced to a formula—you can map a pathway to success. Reliability lets us measure how successful we are likely to be when we undertake an activity, or do a project, or go on a mission, or run an organisation, or use plant and equipment to make a product.

This understanding of what is reliability, and that reliability is an invention, gives us a fourth definition for reliability, “Reliability is a result of creating and building a thing that can do the duty, and preventing its failure during use.”

We have control over reliability because we have control over the chance of success. We control chance by the design, the manufacture, the assembly, the installation, the operation, and the maintenance of what we do. This means you can have world-class plant, equipment, and machine reliability by maximising the chance of success at every point in the life-cycle of your equipment and its parts.

If you want world class reliability, then you will need to ensure failure-free design, manufacture, assembly, installation, operation, and maintenance is always done to your plant and equipment. That is the exact purpose and duty of a Plant Wellness Way EAM system-of-reliability.


This slide is a companion to the new Industrial and Manufacturing Wellness book. The book has extensive information, all the necessary templates, and useful examples of how to design and build your own Plant Wellness Way enterprise asset life cycle management system-of-reliability. Get the book from its publisher, Industrial Press, and Amazon Books.

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