Page 75 - Intro Predictive Maintenance

66 An Introduction to Predictive Maintenance

of unscheduled delays? Yes, it will, but it will do little or nothing to reduce costs,
improve availability, or increase bottom-line profits. The unfortunate part is that too
many programs are judged solely on the number of measurement points acquired each
month, how many points are in alarm, or the number of unscheduled delays. As a result,
a program is viewed as being successful even though it is actually increasing costs.

What Would You Change?
Perhaps the most interesting results of the survey were the responses to questions per-
taining to improvements or changes that should be made to these existing programs.
The responses included the following:

Do More Often. One of the favorite ploys used by upper management to reduce the
perceived cost of predictive maintenance is to reduce the frequency of use. Instead of
monitoring equipment on a frequency equal to its criticality, they elect to limit the fre-
quency to quarterly, semi-annually, or even less. This approach will ensure failure or
at best restrict the benefits of the program. To be effective, predictive maintenance
technologies must be used. Limiting the evaluation cycle to abnormally long intervals
destroys the program’s ability to detect minor changes in critical plant equipments’
operating condition.

The proper monitoring frequency varies depending on the specific technology used
and the criticality of the plant system. For example, plant systems that are essential
for continued plant operation should be monitored continuously. Systems with lesser
importance may require monthly or annual evaluation frequencies.

When vibration monitoring is used, the maximum effective frequency is every 30
days. If the frequency is greater, the program effectiveness will be reduced in direct
proportion to the analysis interval. In most cases, programs that use a monitoring
frequency greater than 30 days for noncritical plant systems will never recover the
recurring costs generated by the program. Thirty days is the maximum interval
recommended for this program type. As the criticality of the plant system increases,
so should the monitoring frequency.

Some applications for thermography, such as roof surveys, should have an interval of
12 to 36 months. Nothing is gained by increasing the survey frequency in these types
of applications; however, other applications, such as monitoring electrical equipment
and other critical plant systems, should follow a much more frequent schedule. Similar
to vibration monitoring, the monitoring frequency for thermographic programs should
be based on the criticality of the system. Normal intervals range from weekly on essen-
tial systems to bimonthly on less critical equipment.

Lubricating oil analysis, when used properly, does not require the same frequency as
other predictive maintenance technologies. Because this technique is used solely to
evaluate the operating condition of lubricants, a quarterly or semi-annual evaluation
is often sufficient. Too many programs use a monthly sampling frequency in the mis-