Page 81 - Intro Predictive Maintenance

72 An Introduction to Predictive Maintenance

A side benefit of predictive maintenance is the automatic ability to monitor the mean-
time-between-failures (MTBF). These data provide the means to determine the most
cost-effective time to replace machinery rather than continue to absorb high mainte-
nance costs. The MTBF of plant equipment is reduced each time a major repair or
rebuild occurs. Predictive maintenance will automatically display the reduction of
MTBF over the life of the machine. When the MTBF reaches the point that contin-
ued operation and maintenance costs exceed replacement cost, the machine should be
replaced.

In each of the surveyed plants, the availability of process systems was increased after
implementation of a condition-based predictive maintenance program. The average
increase in the 500 plants was 30 percent. The reported improvement was based
strictly on machine availability and did not include improved process efficiency;
however, a full predictive program that includes process parameters monitoring can
also improve the operating efficiency and therefore productivity of manufacturing and
process plants. One example of this type of improvement is a food manufacturing
plant that decided to build additional plants to meet peak demands. An analysis of
existing plants, using predictive maintenance techniques, indicated that a 50 percent
increase in production output could be achieved simply by increasing the operating
efficiency of the existing production process.

The survey determined that advanced notice of machine-train and systems problems
had reduced the potential for destructive failure, which could cause personal injury or
death. The determination was based on catastrophic failures where personal injury
would most likely occur. Several insurance companies are offering premium reduc-
tions to plants that have a condition-based predictive maintenance program in effect.
Several other benefits can be derived from a viable predictive maintenance manage-
ment program: verification of new equipment condition, verification of repairs and
rebuild work, and product quality improvement.

Predictive maintenance techniques can be used during site acceptance testing to deter-
mine the installed condition of machinery, equipment, and plant systems. This
provides the means to verify the purchased condition of new equipment before accep-
tance. Problems detected before acceptance can be resolved while the vendor has a
reason—that is, the invoice has not been paid—to correct any deficiencies. Many
industries are now requiring that all new equipment include a reference vibration
signature provided with purchase. The reference signature is then compared with
the baseline taken during site acceptance testing. Any abnormal deviation from the
reference signature is grounds for rejection, without penalty of the new equipment.
Under this agreement, the vendor is required to correct or replace the rejected equip-
ment. These techniques can also be used to verify the repairs or rebuilds on existing
plant machinery.

Vibration analysis, a key predictive maintenance tool, can be used to determine
whether the repairs corrected existing problems and/or created additional abnormal