to A Healthy Machine by James W. Taylor,
Management Solutions, Inc.
Most condition assessment programs in industry
concentrate on one or two technologies. The people,
procedures and practices are tailored to those
technologies. Application of the technology is
optimized, rather than the results. This paper advocates
a machine centered, as opposed to a technology centered,
approach to the assessment of the condition of
machinery. Just as your physician uses a variety of
tests and evaluations to assess your state of health, we
should do the same for our machinery. To do less means
we make decisions based on incomplete information.
have a condition assessment program in place; usually
those programs operate in relative isolation,
concentrating on only one or two technologies. The
people responsible for them work to maximize the
efficiency of the application of the technology.
Therefore the application of the technology is
optimized, rather than the results.
machine-centered, as opposed to a technology-centered,
approach to condition assessment will maximize the
effectiveness of technology in improving machine
reliability. This approach focuses on those tests and
tasks that are cost effective when it comes to machine
A plants condition assessment program might include
vibration monitoring, oil analysis and thermography. And
they may also have preventive maintenance tasks calling
for routine overhaul of some machines based on running
time or calendar time. This has the potential to make
major contributions to the reliability of the machinery.
But usually, these various sets of data never meet. And
the routine overhaul ó itís not effected by collected
data. So the payback is never fully realized.
consider the typical vibration program. After some
research, a cost justification is made and approved to
purchase vibration equipment and software. Then one or
two technicians are trained and designated to manage the
program. They are told to make the vibration program
run. In the absence of any measure of cost-benefit, they
make the decision to apply the vibration to as many
pieces of equipment as possible. From their perspective,
itís a smart move: it spreads the cost of equipment and
training over as many pieces of equipment as possible,
minimizes cost per measurement, provides a full work
load, and keeps the equipment in use. It optimizes the
individual technology program.
Is this the
best strategy to improve machine reliability? Would you
be happy with your doctor if on your annual physical he
only tested your pulse rate? And then maybe he makes a
decision on whether to do surgery based on that? (That
pump overhaul is surgery!) Probably not! Youíd like to
see him make a number of tests ó blood work, EKG, chest
x-ray, etc. Then heíll get a complete picture of your
health. And have a lot better basis to make a decision
principle applies to machinery. To get a complete
picture of machine health, you need to run a number of
tests. And when that PM for overhaul (surgery) comes up,
you can make an informed decision on whether to perform
or defer it.
assessment involves a lot more parameters than just
vibration, oil condition and IR. Process parameters such
as temperatures, pressures, flow rates and operating
speed all have things to tell us about health of our
machinery. For example, suction and discharge pressure
of a pump, along with motor amps, RPM and flow rate will
give a good indicator of impellor condition. Based on
those, you may decide to defer that pump overhaul for
another year or two. Thatís a big savings.
If you have
a technician going to a machine to collect data for one
technology, why not collect all the data you need?
Instead of just vibration, how about trending bearing
temperatures, fluid pressures, RPM and other parameters
that contribute to a complete picture of the machines
health. It means that more time will be spent at each
machine, and fewer machines will be assessed in a day.
But you have much more valuable information. You will
also save transit time, prep time, and administrative
time associated with multiple trips to the machine. And
youíll save time by just applying a technology to those
machines where itís cost effective. You havenít
optimized the technology, but you have optimized the
machineís healthcare. And isnít that what we really
want to propose an approach thatís not new or unique.
Many savy maintenance managers have done it for years.
Reliability Centered Maintenance formalizes it. I call
it Machine Centered Healthcare.
that Reliability Centered Maintenance is the best
approach for critical machines. But not every plant can
afford, can get approval, or has the manpower for a
Reliability Centered Maintenance program. Itís expensive
in the short run. Iím proposing a thought process that
will help you decide how to maintain your machines in a
less formal manner with less paperwork than reliability
machinery-centered approach looks at the machine first,
and by asking a series of questions, helps you decide
how to maintain the machineís health. What tests should
be done? What routine PM should be done? How can we make
the overhaul/no-overhaul decision?
First Ask, What Are The Possible
Failures?: To ask what the
failure are, first we need to know what the machine is
supposed to do. What is its primary function? At first
glance, you might say that a pumpís primary function is
to pump a liquid. In reality, its primary function is to
keep a supply tank full. As the process draws liquid
from the tank, the pump replaces it. If the pump canít
pump at a sufficient rate, the supply tank will go
empty. That minimum rate will vary from process to
process. Look beyond the obvious to the real function of
decided what the machineís function is, ask what can
happen to prevent it from meeting that function. In the
case of the pump, the answer might be the impellor
wearing out reducing available head, bearing failure
causing low RPM, a crack in the casing or worn-out seal
causing liquid to be lost reducing flow, or a number of
other possible failures. At this point, youíre just
brainstorming. Donít consider whether the failure is
likely or has much impact. Weíll do that in the next
step. For now, just get a complete list.
Next Ask, Which Of These Failures Are
Significant?: Now that you
have a list of possible failures, you want to decide
which ones you should worry about. Some failures are so
unlikely that you wonít worry about them; others have
such a low consequence that their impact and cost is
history is the best way to determine how often a failure
occurs and what its impact is. You do have one, donít
can do it without the history. Iíve had success in the
past using a subjective evaluation. Make a list of the
failures and ask two questions: how often does this
occur and whatís the impact on production when it does.
Make it up as a questionnaire. Possible answers are in
below. This may sound simplistic but it works.
Now send the
questionnaires to a cross section of maintenance,
production and management personnel. When you get them
back, average the scores for each item.
significance of a failure is the combination of two
factors: frequency and effect. By taking the score for
frequency score (1 to 5) and multiplying it by the score
for effect (1 to 5) youíll get a composite score for
each failure in the range of 1 to 25. Rank the list by
the composite score. The higher the composite score, the
greater the significance of the failure.
Now you have
to make a judgment call ó which failures should you
worry about? Often, only a few will have a high rank and
you can concentrate on them. Other times most will have
a high rank. This is where your knowledge of the machine
and professional judgment come into play.
Next Ask, How Can We Avoid These
Failures?: Starting at the top
of the list, ask ďhow can we avoid this failure?Ē Is
there some action we can take that will keep the failure
from occurring? Can we change the design? Can we replace
a part that has a predictable wear-out period? Can we
adjust or lubricate to avoid failure? The list you make
here should be the start of your preventive maintenance
list for that machine.
Then Ask, When We Canít Avoid Failure,
How Can We Get An Early Warning?:
There will be some failures that we canít avoid. For
those, we ask ďHow can we detect the failure before it
occurs?Ē What are the symptoms of the failure? Most
failures show symptoms before they happen. A pump may
have to be run faster because of a worn impellor. A
motor may draw more amps because of misalignment or a
seal that is too tight. A coupling may be hot because of
misalignment or lack of lubrication. Make a list for
Then, Tailor A Suite Of Tests To
Detect Those Early Warning Signs:
With a list of symptoms, youíre now in the position to
select tests that measure or detect that symptom. For
each symptom, try to get as many independent tests as
possible. The more information you have, the more
confident youíll be in your call. You should have at
least two tests for each failure that can confirm each
other and avoid false positives (or negatives).
considering tests, donít limit yourself to high tech
methods. Process parameters are also valuable. And one
of the most valuable tests is the operator and
maintainer. An experienced person, familiar with the
machine, making a conscious effort to sense a particular
effect, can be very effective at assessing the health of
Finally, Collect The Results Of The
Tests At One Decision Point:
Doing the tests without putting all the information
together is not effective. I recommend that each machine
have one or two individuals assigned to monitor its
health. They should be trained in assessing all the
information provided by the tests. Notice I didnít say,
ďtrained to evaluate the dataĒ. They donít have to
analyze the data (vibration spectra); they just have to
understand the results (information) of that analysis.
receive the results of the tests along with any other
pertinent information on a regular basis. Then they can
use that information to manage the machine. They can use
it to adjust lubrication intervals, decide when
adjustments are needed or part replacement is indicated.
And that overhaul? They may decide itís not needed after
Condition assessment programs are often structured to
optimize the application of the technology. This spreads
the cost of equipment and training over as many pieces
of equipment as possible, minimizes cost per
measurement, provides a full work load, and keeps the
equipment in use. But it means that we may be spending
time and resources taking data that is not particularly
valuable in improving reliability and reducing costs.
And the information derived does not get integrated into
overall machine healthcare decisions.
What we want
to do is to maximize the effectiveness of the technology
in improving machinery reliability. We need to assess
machine health based on several measures. And we should
only do those tests and tasks that are cost effective
from the point of view of the machine. The question is,
how do we decide what to do? I propose we follow a
systematic process to identify that.
the process is:
First ask, what
are the possible failures?
Next ask, which
of these failures are significant?
Next ask, how can
we avoid these failures?
Then ask, when we
canít avoid failure, how can we get an early
Then, tailor a
suite of tests to detect those early warning signs.
the results of the tests at one decision point.
information please contact the author:
Management Solutions, Inc.
Clarks Hill, IN 47930
Editors note: Our thanks goes to James for this
article - as the first a what we hope is a long series
of common sense "how to" articles. Stay tuned. - Terry O