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Reliability and Maintenance Management
Consultant Idhammar is president of IDCON,
Raleigh, NC, a reliability and maintenance
management consulting firm, specializing in education, training and
implementation of improved operations, reliability,
and maintenance management practices.
Feedback on this reliability
article is appreciated. Send to info@idcon.com
For plant
maintenance consulting information. Please call (919) 847 8764.
More information available in our reliability
and maintenance books |
For decades, many “experts” have used the graph in Figure
1 to discuss the optimum level of maintenance. This Figure is based on
an old-fashioned, yet widespread approach that bases preventive maintenance
on Fixed Time Maintenance (FTM) replacements and overhauls of components.
This approach is seldom justifiable because only 15% to 20% of all components
fail after a predictable time.
As the graph shows, the more this type of maintenance is performed, the
larger the cost for preventive maintenance becomes. Concurrently, the
cost for corrective maintenance is supposed to go down. The cost for production
losses is believed to go down to a point where you need to shut down equipment
more frequently for preventive maintenance, and, as a result, the cost
of lost production starts increasing.
The top total curve in Figure 1 is the sum of the other curves and shows
what the optimum level of maintenance should be.
THE RIGHT APPROACH. A modern and cost-effective
approach to preventive maintenance shows that there is no maintenance
cost optimum. Instead, maintenance costs will decrease at the same time
as costs for production losses also decrease. This approach can be summarized
as follows.
No preventive maintenance action is performed unless proven to be less
costly then the failure. A simple consequence of failure analysis (CFA)
is made to justify preventive maintenance activities.
Preventive maintenance activities are primarily condition-based. The condition
of a component, measured when the equipment is in operation, governs planned
and scheduled corrective maintenance. It is acceptable to operate a component
to breakdown when it is the most cost-effective maintenance procedure.
A standard corrective maintenance procedure should be developed and documented.
Define the need for corrective maintenance early on (Condition Monitoring)
as a part of preventive maintenance. Correcting the problem is defined
as planned and scheduled maintenance.
Practicing this maintenance philosophy will transform the earlier graph
to that of Figure 2. Here, the cost for preventive maintenance is very
low, especially if operators are trained and motivated to do some essential
care and inspections. A plant might end up having less than 5% of the
traditional work force allocated for preventive maintenance. As with Figure
1, the top total curve in Figure 2 is the sum of the other curves and
shows what the optimum level of maintenance should be.
With this improved maintenance philosophy, the level of planned and scheduled
corrective maintenance will increase to over 80% and total maintenance
volume and costs will go down 20% to 30%.
More significantly, reliability will improve and production throughput
will be faster. This results in lower costs for lost production. And,
because preventive maintenance activities are cost-justified based on
failure-developing periods and failure distribution in time, total costs
are continuously decreasing.
Figure 1:Wrong approach to maintenance
Figure 2: Right approach to maintenance
Consider Preventive Maintenance training and implementation support from
IDCON. More
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