Page 22 - Machinery Component Maintenance

8 Machinery Component Maintenance and Repair

dicted and its consequence reduced by perhaps continuous or daily
surveillance.
3. Select PM task.
4. Determine normal life span before defect, failure, or deterioration
mode will develop.
5. Choose PM interval within normal life span.
6. Determine who should do the job-operating crew or maintenance
personnel.

More often than not we will find that machinery failure modes are
probabilistic and indeterminate. PM will therefore not help and predic-
tive strategies are indicated: By continuously looking for problems, we
expect not to reduce the deterioration rate of machinery components, but
to control the consequences of unexpected defect or failure. This mainte-
nance strategy is often referred to as predictive- or condition-based main-
tenance. Together with “post mortem” failure analysis8, this strategy is
the most powerful weapon in the arsenal of the machinery maintenance
person. Figure 1-5 shows how predictive maintenance works in connec-
tion with large petrochemical process machinery such as turbocompres-
sors, reciprocating compressors, and their drivers.
The fundamental difference between preventive maintenance and pre-
dictive- or condition-based maintenance strategies is that PM is carried
out as soon as a predetermined interval has elapsed, while condition-
based maintenance requires checking at predetermined intervals, with the
maintenance action carried out only if inspection shows that it is re-
quired. The main factors in a predictive machinery maintenance program
are:

0 State-of-the-art instrumentation and monitoring methods as shown in
Table 1-1.
Skilled analysts.
Information system allowing easy data retrieval.
Flexible maintenance organization allowing for an easy operations/
maintenance interface.
0 Ability to perform on-line analysis’ * .

In the following chapters we will further deal with predictive mainte-
nance tools.