Page 15 - An Introduction To Predictive Maintenance

Impact of Maintenance 5

Predictive maintenance is much more, however. It is the means of improving pro-
ductivity, product quality, and overall effectiveness of manufacturing and production
plants. Predictive maintenance is not vibration monitoring or thermal imaging or lubri-
cating oil analysis or any of the other nondestructive testing techniques that are being
marketed as predictive maintenance tools.

Predictive maintenance is a philosophy or attitude that, simply stated, uses the actual
operating condition of plant equipment and systems to optimize total plant operation.
A comprehensive predictive maintenance management program uses the most cost-
effective tools (e.g., vibration monitoring, thermography, tribology) to obtain the
actual operating condition of critical plant systems and based on this actual data
schedules all maintenance activities on an as-needed basis. Including predictive main-
tenance in a comprehensive maintenance management program optimizes the avail-
ability of process machinery and greatly reduces the cost of maintenance. It also
improves the product quality, productivity, and profitability of manufacturing and
production plants.

Predictive maintenance is a condition-driven preventive maintenance program. Instead
of relying on industrial or in-plant average-life statistics (i.e., mean-time-to-failure) to
schedule maintenance activities, predictive maintenance uses direct monitoring of the
mechanical condition, system efficiency, and other indicators to determine the actual
mean-time-to-failure or loss of efficiency for each machine-train and system in the
plant. At best, traditional time-driven methods provide a guideline to “normal”
machine-train life spans. The final decision in preventive or run-to-failure programs
on repair or rebuild schedules must be made on the basis of intuition and the personal
experience of the maintenance manager.

The addition of a comprehensive predictive maintenance program can and will provide
factual data on the actual mechanical condition of each machine-train and the oper-
ating efficiency of each process system. This data provides the maintenance manager
with actual data for scheduling maintenance activities. A predictive maintenance
program can minimize unscheduled breakdowns of all mechanical equipment in the
plant and ensure that repaired equipment is in acceptable mechanical condition. The
program can also identify machine-train problems before they become serious. Most
mechanical problems can be minimized if they are detected and repaired early. Normal
mechanical failure modes degrade at a speed directly proportional to their severity. If
the problem is detected early, major repairs can usually be prevented.

Predictive maintenance using vibration signature analysis is predicated on two basic
facts: (1) all common failure modes have distinct vibration frequency components
that can be isolated and identified, and (2) the amplitude of each distinct vibration
component will remain constant unless the operating dynamics of the machine-
train change. These facts, their impact on machinery, and methods that will identify
and quantify the root cause of failure modes are developed in more detail in later
chapters.