Preventive Maintenance
Buddhika Lewangama
Marriott School
November 2006
Agenda
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Definition of Preventive Maintenance (PM)
Reasons for the increased need of PM
Advantages of a PM system
Risks of running a PM system
When to use a PM system
The law of PM
Guide to a successful PM system
Execution process
Conclusion
Readings
What is Preventive Maintenance?
• Preventive maintenance is a schedule of planned
maintenance actions aimed at the prevention of
breakdowns and failures. The primary goal of
preventive maintenance is to prevent the failure of
equipment before it actually occurs. It is designed
to preserve and enhance equipment reliability by
replacing worn components before they actually
fail.
Reasons for the need of a PM system
• Increased Automation
• Business loss due to production delays
• Production of a higher quality product
• Just-in-time manufacturing
• Need for a more organized, planned environment
Advantages of a PM system
• 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.
• Timely, routine repairs circumvent fewer large-scale
repairs.
Continued • Reduced cost of repairs by reducing secondary failures.
When parts fail in service, they usually damage other parts.
• Better quality products
• Identification of equipment with excessive maintenance
costs
• Improved safety and quality conditions.
Brainstorming Exercise
• Are there any risks of running a PM system?
• If there are risks when would it be a good time to
use PM?
Potential errors or damage
of a PM system
• Damage to an adjacent equipment during a PM task.
• Reintroducing infant mortality by installing new parts or
materials.
• Damage due to an error in reinstalling equipment into its
original location.
A real life example of a PM error
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
our point. The data collected from those plants 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.
When Does Preventive Maintenance Make
Sense
• This is a logical choice that considers two conditions
– #1. The component in question has an increasing failure rate.
– #2. The overall cost of the preventive maintenance action must be
less than the overall cost of a corrective action.
If both of these conditions are met PM would make sense
The Law of PM
• Higher the value of the plant assets and equipment
per square foot of plant, the greater will be the
return on a PM program.
E.g. - 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 wellmanaged plant can afford not to develop a PM program.
How to determine the optimum age of
replacement?
How to determine the optimum age of
replacement?
• A more technical approach.
Where:
• R(t) = reliability at time t.
• CP = cost of planned replacement.
• CU = cost of unplanned replacement
• CPUT(t) = The optimum replacement time
The key for a successful PM
system
• Scheduling – Should be automated to the maximum
extent possible
• Execution – Should be done before the actual break
down occurs.
Execution
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The Bath Tub Model – Three
stages of new parts
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2.
3.
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Infant morality stage
A fairly long run stage
Wear out stage
Traditional View according to
Bath Tub Model – Replace
components just before they
entered wear out stage
Execution
• Traditional view says –
Wear out stage = Increased rate of failure.
• Point to Ponder –
Since, wear out stage represents increased rate of
failure, wouldn’t it be plausible to execute the PM program
at this stage?
Execution
• United Airlines Research
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.
What really should PM focus on?
• Cleaning
• Lubrication
• And correcting deficiencies
Found through testing
and inspection
Predetermined parts replacement should be minimal and done only where statistical evidence clearly
indicates wear-out characteristics
In the absence of data
• Age exploration programs
• Statistical analysis
Cost shouldn’t be a primary factor in deciding against data
collection for a PM
Motivating Preventive Maintenance
Workers
• Training programs – most effective
• Establish inspection and preventive maintenance as a
recognized, important part of the overall maintenance
program.
• Assign competent, responsible people to the preventive
maintenance program.
Continued • 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
Summary
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PM is not difficult to achieve.
It is an essential part for cost reduction
There is an element of risk involved in PM
Careful planning and execution will reduce the risk of
PM
• 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.
Readings
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John M Gross, “Fundementals of Preventive Maintenance”, American
Management Association, Pg 228
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Richard D Palmer, “Maintenance Planning and Scheduling Handbook”, ch1pg.30
•
“Is Preventive Maintenance Necessary?”, 28 Nov.2006 <
http://www.reliability.com/articles/article37.htm>
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“The Reliability Hotwire, the eMagazine for the Reliability Professional”,
Issue 21, Nov. 2002 http://www.weibull.com/hotwire/issue21/hottopics21.htm
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“Preventive Maintenance”, Reliasoft Coporation, 28 Nov
2006http://www.weibull.com/SystemRelWeb/preventive_maintenance.htm