Is Preventive Maintenance Necessary?
William C. Worsham, Reliability Center,
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
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
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
- Better conservation of assets and increased life expectancy
of assets, thereby eliminating premature replacement of machinery
- 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.
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
- Reintroducing infant mortality by installing new parts
- Damage due to an error in reinstalling equipment into its
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
- 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.
E. T. Newbrough, Effective Maintenance Management, (New
York: McGraw-Hill, 1967).