What is Reliability

Why 'Reliability' may not actually be what you’re looking for

It’s more about identifying KPI’s that support your study objective

We've heard our clients say, "I need my plant to be more reliable." Or "We need a reliability study done." Some might say that this is improper use of terminology, or even infer that you don’t really know what you want. We know what you are asking for. You want to find optimum value created by spending capital to reduce the frequency and duration of unintended events and their ensuing consequences. You are already asking the questions that get this process started.

What is the definition of reliability ?

It depends on who you ask. There exists a formal definition given by MIL-STD-721C: The probability that an item will perform its intended function for a specified interval under stated conditions.

When the term reliability is used in the process industries, it usually isn't used with this definition in mind.

Some organizations have their own definition which identifies reliability as a Key Performance Indicator (KPI) that is a measure of the ratio of actual to perfect production quantities. This is a measurement of plant utilization rather than the military standard defined reliability.

Mostly, reliability is simply used as a general term that describes activities related to the study and analysis of system performance taking into account naturally occurring system failures.

Regardless of how reliability is defined, it is important to start any study with a well-defined objective including - increasing plant up time, designing for greater asset reliability, or determining optimum number of spares. Objectives are typically related to a desire to increase revenue.

A well-defined objective is the key to project success

Once the objective is clear, we can identify Key Performance Indicators (KPI's) that will help support and quantify the benefits derived from the asset reliability modeling study. These KPI's should be well defined within the context of the study to avoid confusion and results misinterpretation. Ideally, the accepted definitions of such KPI's would be standardized across the organization.

A variety of KPI's may be identified that directly affect the objectives under study such as availability, reliability, on stream time, failures on demand, storage tank empty/full events, among others.

The questions you should be asking a potential consultant

  • What kind of experience do you have?
  • Have you actually worked in the process industries before? (Many have but many have not.)
  • What kind of software tools do you use, or have access to?
  • Who have you done work for?
  • Are you familiar with reliability studies that deal with continuous flows, buffer storage, warehouse storage, complex logic? (Everyone will say yes but dig deeper, most will be making lots of assumptions in this area)

More important than identifying which is the "proper" definition of Reliability, is simply identifying KPI's that support your study objective, and having the tools and skills that are flexible enough to adapt to measuring and quantifying those KPI's.

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