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Reliability
Centered Maintenance has changed the way we think about Preventive
Maintenance (PM). It has caused some to question whether it is even
necessary to do preventive maintenance. The truth is most manufacturing
facilities would benefit from a good preventive maintenance program. It
would be especially beneficial for those plants that rely on breakdown
or run-to-failure maintenance. But, a preventive maintenance program is
potentially risky, so it must be administered and performed properly to
be successful. This paper will examine both the benefits and risks of
preventive maintenance and offer some ideas on how to make it
successful. We will start with a definition of preventive maintenance.
What
is Preventive Maintenance?
Preventive
maintenance is planned maintenance of plant and equipment that is
designed to improve equipment life and avoid any unplanned maintenance
activity. PM includes painting, lubrication, cleaning, adjusting, and
minor component replacement to extend the life of equipment and
facilities. Its purpose is to minimize breakdowns and excessive
depreciation. Neither equipment nor facilities should be allowed to go
to the breaking point. In its simplest form, preventive maintenance can
be compared to the service schedule for an automobile.
A
bona fide preventive maintenance program should include:
- Non-destructive
testing
- Periodic
inspection
- Preplanned
maintenance activities
- Maintenance
to correct deficiencies found through testing or inspections.
The
amount of preventive maintenance needed at a facility varies greatly. It
can range from a walk through inspection of facilities and equipment
noting deficiencies for later correction up to computers that actually
shut down equipment after a certain number of hours or a certain number
of units produced, etc.
Many
reasons exist for establishing a PM program. Listed below are a few of
these. Whenever any of these reasons are present, a PM program is likely
needed.
Reasons
for Preventive Maintenance
- Increased
Automation
- Business
loss due to production delays
- Reduction
of insurance inventories
- Production
of a higher quality product
- Just-in-time
manufacturing
- Reduction
in equipment redundancies
- Cell
dependencies
- Minimize
energy consumption (5% less)
- Need
for a more organized, planned environment
Why
Have a PM Program
The
most important reason for a PM program is reduced costs as seen in these
many ways:
- Reduced
production downtime, resulting in fewer machine breakdowns.
- Better
conservation of assets and increased life expectancy of assets,
thereby eliminating premature replacement of machinery and
equipment.
- Reduced
overtime costs and more economical use of maintenance workers due to
working on a scheduled basis instead of a crash basis to repair
breakdowns.
- Timely,
routine repairs circumvent fewer large-scale repairs.
- Reduced
cost of repairs by reducing secondary failures. When parts fail in
service, they usually damage other parts.
- Reduced
product rejects, rework, and scrap due to better overall equipment
condition.
- Identification
of equipment with excessive maintenance costs, indicating the need
for corrective maintenance, operator training, or replacement of
obsolete equipment.
- Improved
safety and quality conditions.
If
it cannot be shown that a preventive maintenance program will reduce
costs, there is probably no good reason other than safety to have a PM
program.
The
Law of PM Programs
There
are many advantages for having a good preventive maintenance program.
The advantages apply to every kind and size of plant. The law of PM
programs is that the higher the value of plant assets and equipment per
square foot of plant, the greater will be the return on a PM program.
For instance, downtime in an automobile plant assembly line at one time
cost $10,000 per minute. Relating this to lost production time an
automobile manufacturer reported that the establishment of a PM program
in their 16 assembly plants reduced downtime from 300 hours per year to
25 hours per year. With results such as this no well-managed plant can
afford not to develop a PM program.[1]
Preventive
Maintenance Program Risks
As
mentioned in the beginning of this report, preventive maintenance does
involve risk. The risk here refers to the potential for creating defects
of various types while performing the PM task. In other words, human
errors committed during the PM task and infant mortality of newly
installed components eventually lead to additional failures of the
equipment on which the PM was performed. Frequently, these failures
occur very soon after the PM is performed. Typically, the following
errors or damage occur during PM’s and other types of maintenance
outages.
- Damage
to an adjacent equipment during a PM task.
- Damage
to the equipment receiving the PM task to include such things as:
- Damage
during the performance of an inspection, repair, adjustment, or
installation of a replacement part.
- Installing
material that is defective, incorrectly installing a replacement
part, or incorrectly reassembling material.
- Reintroducing
infant mortality by installing new parts or materials.
- Damage
due to an error in reinstalling equipment into its original
location.
Especially
disturbing about these types of errors is the fact that they go
unnoticed – until they cause an unplanned shutdown. There is some
published data that illustrates this point. It comes from the
fossil-fuel power industry.
A
review of the data from fossil-fueled power plants that examined the
frequency and duration of forced outages after a planned or forced
maintenance outage reinforces this concept. That data showed that of
3146 maintenance outages, 1772 of them occurred in less than one week
after a maintenance outage. Clearly, this is pretty strong evidence that
suggests that in 56% of the cases, unplanned maintenance outages were
caused by errors committed during a recent maintenance outage.
Having
performed and supervised many industrial PM’s, I also support this
concept. I can remember many instances where it would take days after a
PM was performed to get everything back to normal. This was particularly
true when many components that came in contact with the product being
produced were replaced. I remember working with the quality people on
many occasions to insure that every position on a multiple position
machine was once again producing first quality product. Many times it
required adjusting and/or replacing components that were adjusted or
replaced on the PM.
How
to Have a Successful PM Program
The
key to a successful Preventive Maintenance (PM) program is scheduling
and execution. Scheduling should be automated to the maximum extent
possible. Priority should be given to preventive maintenance and a very
aggressive program to monitor the schedule and ensure that the work is
completed according to schedule should be in place.
Preventive
Maintenance Execution
Traditional
preventive maintenance was based on the concept of the bathtub curve.
That is, new parts went through three stages, an infant mortality stage,
a fairly long run stage, and a wear-out stage. The PM concept was to
replace these parts before they entered the wear-out phase.
Unfortunately, Reliability Centered Maintenance based on research done
by United Airlines and the rest of the aircraft industry showed that
very few non-structural components exhibit bathtub curve
characteristics. Their research showed that only about 11% of all
components exhibit wear-out characteristics, but 72% of components do
exhibit infant mortality characteristics. These same characteristics
have been shown to apply in Department of Defense systems as well as
power plant systems. It is very likely that they apply universally as
well. Therefore, they should be taken into account when configuring
preventive maintenance on industrial equipment.
In
order to have a successful PM program, the message is clear. The PM
should focus on cleaning, lubrication, and correcting deficiencies found
through testing and inspections. When there is a need to adjust or
replace components, it should be done by highly trained and motivated
professionals. Predetermined parts replacement should be minimal and
done only where statistical evidence clearly indicates wear-out
characteristics. In the absence of data to support component
replacement, an age exploration program or the collection of data for
statistical analysis to determine when to replace components should be
initiated. Borrowing from the Japanese, lubrication points should be
clearly marked with bright red circles to ensure that lubrication tasks
are not missed. Cleaning should be carried our to remove dust, dirt, and
grime because these things mask defects that can cause unplanned
maintenance outages.
Motivating
Preventive Maintenance Workers
A
quality preventive maintenance program requires a highly motivated
preventive maintenance crew. To provide proper motivation, the following
activities are suggested:
- Establish
inspection and preventive maintenance as a recognized, important
part of the overall maintenance program.
- Assign
competent, responsible people to the preventive maintenance program.
- Follow-up
to assure quality performance and to show everyone that management
does care.
- Provide
training in precision maintenance practices and training in the
right techniques and procedures for preventive maintenance on
specific equipment.
- Set
high standards.
- Publicize
reduced costs with improved up-time and revenues, which are the
result of effective preventive maintenance.
In
addition to explaining the importance of a good preventive maintenance
program and the benefits that can be derived from it, training is
probably the most effective motivational tool available to the
maintenance supervisor. Maintenance and training professionals have
estimated that a company should spend $1200 per year for training of
supervisors and $1000 per year for each craftsperson. In fact, due to
advances in technology, if the company has not provided any training for
craftspeople in the past 18 months, their skills have become dated.
Conclusion
It
is possible to have a successful preventive maintenance program. From a
cost reduction viewpoint it is essential, but it does entail risk. When
the proper care is taken, the risks, however, can be minimized. In order
to minimize risk, preventive maintenance has to be carefully planned and
carried out by well-trained and motivated workers. The biggest benefits
of a PM program occur through painting, lubrication, cleaning and
adjusting, and minor component replacement to extend the life of
equipment and facilities.
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