Efficient Plant May 2019 - 30

Answers to questions
facing today's reliability
& maintenance
professionals

department | on the floor

FMEA or Q
RCM: Is
A
There a
Difference?

Should I do a FMEA or
RCM to resolve a
machine issue?

Dr. Klaus M. Blache
Univ. of Tennessee Reliability
and Maintainability Center
(RMC)

30

| EFFICIENTPLANTMAG.COM

The short answer is that it
depends on several things,
primarily frequency of occurrence
and severity of the failure mode.
I frequently am asked, what's the
difference between doing an FMEA
(failure mode and effects analysis) and
an RCM (reliability-centered maintenance) evaluation?
FMEAs were originally directed at
improving product, machinery, and
equipment at the design stage. Use
of them began in the military in the
late 1940s, were implemented in the
aerospace industry in the 1960s, and
spread to manufacturing in subsequent years. In 1983, Stan Nowlan
(United Airlines) collaborated with
John Moubray to deliver the message
to industry that led to Moubray's RCM
II book (1977, Industrial Press), which
is a key RCM reference.
In simplest terms, an FMEA is a
standardized methodology used to
identify potential failure modes for a
product/process/machine. FMEAs use
three scales (severity, occurrence, and
detection), to assess each failure-mode
risk. Failure modes are ranked, based
on a risk-priority number (three scales
multiplied together). The final step is
to correct the undesired items. Note
that, in some situations, the preferred option would be run to failure.
After performing several FMEAs, it
becomes evident (with some break-

even calculations) which minimum
risk-priority number (RPN) indicates
required improvement actions. Often,
a severity-versus-occurrence matrix
is constructed to depict relative
importance in terms of elimination
or mitigation. FMEAs should be a
living document that drive continuous
improvement.

RELIABILITY-CENTERED
MAINTENANCE
RCM is also a standardized methodology. It's used to analyze the functions and potential failure modes of a
physical asset (machinery, equipment,
automobile, pump) to remove failures
and develop an ongoing maintenance
plan. RCM addresses risk, operations,
and cost and attempts to remove all
failures (not just those above a specified RPN number, as with FMEAs).
For those reasons, RCM provides
a more-detailed analysis than an
FMEA. Details on RCM and FMEA
can be found in "Evaluation Criteria
for Reliability-Centered Maintenance
(RCM) Processes" (JA1011_199909,
updated_200908). That was how it
started.
What I see today is that the majority of required work involves machinery and equipment carrying lesser failure consequences than airplanes and
military assets. People are primarily
doing FMEAs and predictive-maintenance optimization (PMO) to
attain better failure-mode mitigation
through engineering changes, or using
a combination of condition-based

MAY 2019


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Efficient Plant May 2019

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