Page 338 - Intro Predictive Maintenance

Establishing a Predictive Maintenance Program 329

maintenance costs. A plant process layout is invaluable during this phase of program
development. It is easy to omit critical machines or components during the audit;
therefore, care should be taken to ensure that all components that can limit produc-
tion capacity are included in your list.

The listing of plant equipment should be ordered into the following classes depend-
ing on the equipment’s impact on production capacity or maintenance cost: Class I,
essential; Class II, critical; Class III, serious; and Class IV, others.
Class I, or essential, machinery or equipment must be online for continued plant
operation. Loss of any one of these components will result in a plant outage and
total loss of production. Plant equipment that has excessive repair costs or repair
parts lead-time should also be included in the essential classification.
Class II, or critical, machinery would severely limit production capacity. As
a rule of thumb, loss of critical machinery would reduce production capacity
by 30 percent or more. Also included in the critical classification are machines
or systems with chronic maintenance histories or that have high repair or
replacement costs.

Class III, or serious, machinery includes major plant equipment that does not
have a dramatic impact on production but that contributes to maintenance
costs. An example of the serious classification would be a redundant system.
Because the inline spare could maintain production, loss of one component
would not affect production; however, the failure would have a direct impact
on maintenance cost.
Class IV machinery includes other plant equipment that has a proven history
of impacting either production or maintenance costs. All equipment in this
classification must be evaluated to determine whether routine monitoring is
cost effective. In some cases, replacement costs are lower than the annual costs
required to monitor machinery in this classification.

The completed list should include every machine, system, or other plant equipment
that has or could have a serious impact on the availability and process efficiency of
your plant. The next step is to determine the best method or technique for cost-
effectively monitoring the operating condition of each item on the list. To select the
best methods for regular monitoring, you should consider the dynamics of operation
and normal failure modes of each machine or system to be included in the program.
A clear understanding of the operating characteristics and failure modes will provide
the answer to which predictive maintenance method should be used.

Most predictive maintenance programs use vibration monitoring as the principal tech-
nique. Visual inspection, process parameters, ultrasonics, and limited thermographic
techniques should also be added to the in-house program. The initial cost of systems
and advanced training required by full thermographic and tribology techniques pro-
hibits their inclusion into in-house programs. Plants that require these techniques
normally rely on outside contractors to provide the instrumentation and expertise
required.