Page 56 - Intro Predictive Maintenance

Role of Maintenance Organization 47

repair activities. This maintenance management approach is predominantly a time-
driven schedule or recurring tasks, such as lubrication and adjustments that are
designed to maintain acceptable levels of reliability and availability.

Reactive. Reactive maintenance is done when equipment needs it. Inspection using
human senses or instrumentation is necessary, with thresholds established to indicate
when potential problems start. Human decisions are required to establish those
standards in advance so that inspection or automatic detection can determine when
the threshold limit has been exceeded. Obviously, a relatively slow deterioration
before failure is detectable by condition monitoring, whereas rapid, catastrophic
modes of failure may not be detected. Great advances in electronics and sensor tech-
nology are being made.

Also needed is a change in human thought process. Inspection and monitoring should
disassemble equipment only when a problem is detected. The following are general
rules for on-condition maintenance:

1. Inspect critical components.
2. Regard safety as paramount.
3. Repair defects.
4. If it works, don’t fix it.

Condition Monitoring. Statistics and probability theory are the basis for condition-
monitoring maintenance. Trend detection through data analysis often rewards the
analyst with insight into the causes of failure and preventive actions that will help
avoid future failures. For example, stadium lights burn out within a narrow period.
If 10 percent of the lights have burned out, it may be accurately assumed that the
rest will fail soon and should, most effectively, be replaced as a group rather than
individually.

Scheduled. Scheduled, fixed-interval preventive maintenance tasks should generally
be used only if failures that cannot be detected in advance can be reduced, or if
dictated by production requirements. The distinction should be drawn between
fixed-interval maintenance and fixed-interval inspection that may detect a threshold
condition and initiate condition-monitoring tasks. Examples of fixed-interval tasks
include 3,000-mile oil changes and 48,000-mile spark plug changes on a car, whether
it needs the changes or not. This may be wasteful because all equipment and their
operating environments are not alike. What is right for one situation may not be right
for another.

The five-finger approach to maintenance emphasizes elimination and reduction of
maintenance needs wherever possible, inspection and detection of pending failures
before they happen, repair of defects, monitoring of performance conditions and
failure causes, and accessing the equipment on a fixed-interval basis only if no better
means exist.