Defining the Importance of Functional Failure

A Critical Component in the Seven Steps of a Complete RCM Analysis

In the 27 years following the release of Nowlan and Heap’s “Reliability Centered Maintenance”, many have struggled to understand the importance of each step in this seven step reliability tool. Over the years, the process has been studied, tested, changed and rearranged as people strive to achieve “world class” levels of reliability with less time and fewer resources. These changes often try to eliminate one or more of the seven steps proven critical in completing a successful effort. In reality, the key to speed in performing your analyses while still maintaining a high quality output is understanding the value in each step of this proven process.

In this article, I will highlight the importance of listing Functional Failures as part of a thorough reliability centered maintenance analysis.

What is the definition of Failure and Functional Failure?

To truly understand the definition of the term Functional Failure, it is important that you first understand Failure. In the past, it was really just Failure that defined and warranted the need for maintenance. Most people looked at Failure as a black or white term – a component either failed or was working – a component was running or shut down. As a result, the world of maintenance in many places became linked to this definition. Maintenance, as a group, were the people you called when the equipment was broken. In reality, the definition of Failure is very broad and can often be subjective. Consider the following definitions of the word Failure: 

Webster’s dictionary defines Failure as “a state of inability to perform a normal function”. 

Nowlan and Heap defined Failure as “an unsatisfactory condition”.

Read these definitions and try to relate them to your equipment or the process you work with. Is it clear to everyone what your “normal functions” are? Does everyone know what a “satisfactory or unsatisfactory condition” is? If we asked everyone who worked with or operated this equipment, would they all have the same definition of Failure, normal functions and unsatisfactory condition? Of course not, and this is what drives us to become more specific in defining Failure. As the definition becomes more specific, our ability to clearly understand and pinpoint Failure increases.

To understand Failure, we must first understand the criteria that defines Failure. This criteria should be set when defining the performance standards for the function of your system (Main Function) and the components that make up the system (Support/ Primary Functions). In defining these performance standards, you will in turn help clearly define what Failure is for your process or equipment. In the world of RCM, we use the term Functional Failure to help clarify the understanding of what Failure is.

Nowlan and Heap defined Functional Failure as “the inability of an item (or the equipment containing it) to meet a specified performance standard.”

Now with the understanding that it’s Functional Failure of an item (component or system) that dictates how we now define Failure, it should now be clear to all people working with or operating the equipment when the equipment has failed.


Writing good Functional Failure Statements

Writing good Functional Failure Statements is clearly dependant on how well your team has defined the functions of your RCM analysis. Some tips to remember as you identify the main and support functions for your equipment:

  • Your Main Function statement should be written in a manor that clearly identifies what the equipment is intended for and all of the performance standards it is expected to maintain including environmental, health and safety standards.
  • Don’t rush through the process of writing function statements; it is, after all, the function statements that create a roadmap to a complete and thorough RCM analysis.
  • Try to identify active and passive functions; this will help to ensure that your team does not miss any hidden function components.

With your function statements complete, you can now begin to identify and list the Functional Failures for your analysis. As an example, I have listed the main function statement for a chilled water system and its corresponding Functional Failures:

Chilled Water System Main/Primary Function Statement:

To be able to supply high quality, chilled water at a temperature of 40°F plus or minus 5°F and a rate of 120 gallons per minute while meeting all environmental, health, and safety standards.

Functional Failures of the Chilled Water System

  1.  Unable to supply chilled water at all
  2. Unable to maintain water temperature above 35° F
  3. Unable to maintain water temperature below 45° F
  4. Unable to supply water at a rate of 120 gallons per minute
  5. Unable to maintain water quality standards
  6. Unable to maintain (company, state or government) environmental, health or safety standards

The importance of listing Functional Failures

With these Functional Failures now identified, it should now be clear to those who operate or maintain the chilled water system when the system is failed. More important, having identified these Functional Failures we can now begin to discuss the causes for each Functional Failure, these are known as Failure Modes. Think about this, for each Functional Failure identified, there are a number of Failure modes that could result in that Functional Failure. Some Failure modes will result in total system shut down or being unable to supply water at all. Some will result in chilled water flow falling below the required 120 gallons per minute. Other Failure modes may affect the quality of the chilled water within the system. The importance of identifying and listing Functional Failures will now become evident within your RCM analysis. In sorting Failure modes by Functional Failure, we begin to create a high level troubleshooting guide for our process or piece of equipment. When this chilled water system RCM analysis is completed, we will have a complete listing of Failure modes that cause each Functional Failure for both operations and maintenance. Now as we operate this process our equipment operators can begin looking for performance trends. If the temperature of the chilled water were to begin to trend up or down they will have a compete listing of the Failure modes that cause these changes.

The pitfalls of skipping Functional Failures

One of the curses of being human is the burning desire to do everything faster. From the time we first learn to walk, we have a desire to run. The minute the first automobile hit the road, someone had to make a faster one. In the world of manufacturing and maintenance, speed can be a good thing, but it can also be a bad thing. From the time Nowlan and Heap first designed and implemented RCM, people have been in search of ways to make it faster and in most cases they do so by eliminating some of the key process steps. In many cases functions and Functional Failures are steps that are eliminated or partly eliminated. In each case the result is an incomplete RCM analysis and an incomplete maintenance strategy. The typical well-meaning attempt to save time is usually driven by an inexperienced facilitator who does not have a full understanding of the consequences or an impatient manager with even less understanding. The list below outlines consequences of skipping functions and or Functional Failures when performing RCM.

Skipping Functions, listing only a main function, or skipping Functional Failures results in:

  • Incomplete listing of Failure mode
  • How can one expect a complete listing of Failures without identifying each component?
  • Incomplete listing of hidden Failures
  • If we don’t discuss each component and its intended function would we expect to discover Failures that are not evident?)
  • The inability to recognize when Functional Failure has occurred
  • Failure to recognize Functional Failure is key in beginning to recognize and understand potential Failures and the P-F Curve
  • Improper applications of Preventive Maintenance and On-Condition Maintenance
  • Functions, Performance Standards and Functional Failures are all key components in understanding the use of on-condition maintenance and predictive technologies. Failure to identify these key components often results in preventive maintenance being applied where on-condition maintenance would be more applicable and effective.
  • An incomplete and therefore less effective maintenance strategy •With all of the above being true how would one expect an effective maintenance strategy as a finished product

In closing, when correctly applied, Reliability Centered Maintenance has a long and successful history as the best process for building a complete and effective maintenance strategy. This success can be easily replicated and achieved through learning the RCM process and sharing our experiences (successes as well as Failures). As RCM practitioners, we also understand that improvement to the process can only come as a result of change to the process and this requires that either steps be added or
eliminated. My advice to those who like myself continuously look to change and improve, if your thinking about eliminating a step, get on the phone or go on the internet and contact a few RCM practitioners and talk about the elimination, chances are most of us have tried it. If you’re looking to add for improvement, try it out, see if it works and adds value, if it does keep it to yourself, you may have a new methodology!

 


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