Failure Modes & Effects Analysis (FMEA) is a structured procedure for achieving improved reliability and continuity of operation in critical equipment and processes. This analysis can be used in many applications, but here the emphasis will be on new equipment or processes proposed for manufacturers that operate on a 24/7 basis. Briefly, the method consists of defining conceivable failure modes, determining the effect of each, assigning weighting factors and deriving numerical results that allow a logical ranking of corrective measures.
It's worth noting that FMEA is most effective when used early in the design or implementation sequence, when modifications are far easier and less expensive than later — when costs of changes and, more importantly, lost production time can be major. This tool can help users move from a reactive to a proactive mode of manufacturing management. Handled correctly, it could be viewed as a form of cheap insurance for the reliability of manufacturing processes.
FMEA is certainly not one of those notorious "flavor-of-the-month" processes or programs. First used in the aircraft industry in the 1950s, it was later adopted by the automotive and aerospace industries and medical equipment manufacturers. These days, software developers and financial analysts use it. It also has become part of the SMRP (Society of Reliability & Maintenance Professionals) "Body of Knowledge" recommended for study by anyone preparing for the Certified Maintenance and Reliability Professional (CMRP) examination. There is justifiable recognition of FMEA's value in many types of applications.
The FMEA procedure
The FMEA evaluation is intended to provide quantitative indicators of failure risk that can be used to effectively rank order implementation of corrective actions. The key derived parameter is known as the Risk Priority Number (RPN). Procedural steps follow:
Some guidelines for using FMEA
FMEA should not be limited to new equipment or processes. Such an analysis also can provide useful information on applying corrective actions when either significant modifications are made to existing equipment or when more-severe service conditions become necessary with the same equipment. In each case, new failure modes or effects that can adversely affect operational continuity, in the absence of compensating changes, may be created.
It can be useful to repeat the FMEA procedure — often more than once — after initial corrective changes resulting from the first iteration have been implemented in the design. These design changes are, of course, done before any fabrication, installation or final purchasing tasks begin. The complexity of the proposed equipment or process will indicate whether repetition of the procedure is justified. Follow-up evaluations may include modified failure modes, effects and values of the S, O and D parameters, created because of design changes from the prior FMEA.
Depending on the given application and availability of funds, corrective actions for all identified failure-mode effects may not be implemented. Those with the highest RPN values will generally produce the biggest "bang for the buck." Keep in mind, however, that application of informed engineering judgment is essential in deciding whether to delete some corrective action(s).
Advantages of FMEA...
Requirements and limitations of FMEA...
Weighing your options
This discussion has only scratched the surface of the Failure Modes & Effects Analysis procedure and some of its characteristics. The references cited at the conclusion of this article present far more information on the subject. Reference 4, in particular, provides cogent arguments to support FMEA and other proactive approaches to reliability.
The major value of up-front FMEA — before the design process or equipment modification has been completed — is that it forces a thorough, logical thinking process at the optimal point in the new design (or design-modification) phase, when corrective changes can and should be made. The keys to success in implementation are management's commitment and establishing a suitable task leader or champion.
In appropriate applications, investment in the FMEA procedure will be insignificant compared with not doing a thorough evaluation and then experiencing major disruptions and expenses during operation — via compromised personnel safety, equipment failure and/or lost production. Although you hope against hope that you'll never need it, it's in anticipation of those types of situations that FMEA can be a very good type of insurance policy. As the TV pitchman said, "You can pay me now or you can pay me later."
Which option will you choose for your operations? MT
1. API Recommended Practice 571, "Damage Mechanisms Affecting Fixed Equipment in the Refining Industry." (This document describes multiple failure modes that can occur in a variety of industries and equipment).
2. Bowles, J.B., "Failure Modes and Effects Analysis," ASM International Handbook, Vol. 11, Failure Analysis and Prevention, 2002, pgs. 50-59.
3. Useful Websites: www.fmeainfocentre.com, www.reliasoft.com, www.weibull.com and www.npd-solutions.com
4. Williamson, Bob, "Getting Operations' Buy-In for Reliability," Maintenance Technology, March 2008, pgs. 6-8.