Page 13 - Intro Predictive Maintenance

4 An Introduction to Predictive Maintenance

Figure 1–1 Typical bathtub curve.

approach is that the mode of operation and system or plant-specific variables directly
affect the normal operating life of machinery. The mean-time-between-failures
(MTBF) is not the same for a pump that handles water and one that handles abrasive
slurries.

The normal result of using MTBF statistics to schedule maintenance is either unnec-
essary repairs or catastrophic failure. In the example, the pump may not need to be
rebuilt after 17 months. Therefore, the labor and material used to make the repair was
wasted. The second option using preventive maintenance is even more costly. If the
pump fails before 17 months, it must be repaired using run-to-failure techniques.
Analysis of maintenance costs has shown that repairs made in a reactive (i.e., after
failure) mode are normally three times greater than the same repairs made on a
scheduled basis.

1.1.3 Predictive Maintenance
Like preventive maintenance, predictive maintenance has many definitions. To some
workers, predictive maintenance is monitoring the vibration of rotating machinery in
an attempt to detect incipient problems and to prevent catastrophic failure. To others,
it is monitoring the infrared image of electrical switchgear, motors, and other electri-
cal equipment to detect developing problems. The common premise of predictive
maintenance is that regular monitoring of the actual mechanical condition, operating
efficiency, and other indicators of the operating condition of machine-trains and
process systems will provide the data required to ensure the maximum interval
between repairs and minimize the number and cost of unscheduled outages created by
machine-train failures.