MRO Today - Reliability vs. maintainability

Reliability vs. maintainability

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Production and maintenance folks are often at odds over equipment performance. The debate frequently involves what to measure and how to measure it. Because of this, I found the need to define two commonly used performance measurement terms: reliability and maintainability.

Confusion stems from many thinking reliability relates to everything about a piece of equipment, including maintainability. Although the terms are closely related, they involve very different approaches to maintenance performance and monitoring. I find the following definitions most useful.

Reliability
Reliability is the probability that a component, equipment or line will complete its assigned work within a defined time period. Think of it as the reflection of the design and operation of a piece of equipment throughout its effective life.

But in reality, the definition is, will the equipment or process work when you want it? Its that simple. Reliability deals with the frequency of failure, so reducing how often something fails improves its reliability and decreases downtime.

When analysis of equipment problems indicates the need to improve reliability (decrease the number of production interruptions) on equipment, consider any of the following actions:
" review operating procedures
" improve installation procedures
" increase predictive (PdM) and preventive (PM) maintenance service
" specify stronger components
" improve operating environment
" modify the equipment
" review maintenance and production scheduling

Maintainability
Maintainability measures the impact failure has on production.

It reflects the speed, difficulty, and cost of repairs and PM/PdM on equipment. Its primary concern is lost production. So, improving asset maintainability reduces downtime. Reduced downtime increases production potential. To improve maintainability (reduce the time of production interruption), look at these:
" installation of standby units
" improve PdM testing
" order or increase the number of spare parts
" order emergency spares
" increase maintenance or operator inspections
" review maintenance or operator training
" provide standby labor
" develop contingency plans
" review maintenance/production scheduling and coordination

While many of these are excellent solutions, having extra parts, people and redundant equipment is an expensive way to improve maintainability. It often makes more sense to initially purchase more costly equipment designed for reliability and maintainability that, in the long run, proves less expensive.

Everybody plays a part
Once you understand the performance measures, who can impact them is the next issue.

Many believe the responsibility and greatest role in equipment reliability and maintainability lies with maintenance. Thats not necessarily true. Production, engineering, purchasing and sales all impact equipment performance.

Maintenance is just one group that influences reliability. Sales and marketing determines the product offering and mix.

Sales determines lead times and lot sizes due to customer expectations. The expectations and offerings set the type and length of product runs. The runs, in turn, determine patterns of equipment wear and tear. These affect breakdown frequency.

Also impacting reliability are:
production, through operating procedures, methods and scheduling equipment for maintenance;
purchasing, by considering life and quality when ordering replacement parts and process materials;
engineering, by determining original equipment specifications and design.

One of the most important ways to improve both reliability and maintainability is planning and scheduling all work or runs. If you read the definitions of both terms, its the only common element on the lists. Scheduling involves developing and following a plan.

A plan ensures the right production status, procedures, parts, resources and people are available. A complex plan needs all the different groups to come together and form a team.

That team works to achieve peak performance for your plant, equipment and systems. Remember, everyones actions impact your reliability and maintainability.

Arne Oas can be reached at .

This article appeared in the February/March 2001 issue of MRO Today magazine. Copyright, 2001.