Page 149 - Improving Machinery Reliability

Machinery Reliability Audits and Reviews 121

Impulse Re a c I lo n
a OM ow
20wow

I WOW0
800 ow
600 wo
dw wo

1
20 000
L I I loom

Figure 3-32. Average probable turbine operating hours for individual components with-
out damage. (From Der Maschinenschaden, Volume 43 (1970), No. 1, pp. 1-40 Allianz
Versicherungs-AG, Munich, Germany. Transcription courtesy of Siemens-America.)

turbines experienced failures which were serious enough to require disbursements
from the insurance carrier.
These failure figures appear to cover only the most serious events. At 0.03 events
per year per steam-turbine driver, the insurer’s statistics might lead us to believe that
we could relax. our audit and review efforts. However, we must keep in mind that our
efforts are aimed not only at eliminating major wrecks but nuisance trips, excessive
downtime, startup delays, and frequent maintenance as well.
It should also be recognized that an awareness of failure causes is necessary for
the effective implementation of machinery reliability audits. For instance, bearing
distress in steam turbines, large electric motors, and associated connected equipment
is often caused by the action of stray electric currents. This type of damage is best
eliminated by the up-front installation of current leak-off brushes, Figure 3-33. A
well-designed leak-off system can be monitored for effectiveness and serviced with
the equipment operating.

Failure Statistics for Gas Turbines

In May, 1980, Allianz Versicherungs-AG of Munich, Germany, released a report
on the failures of modern industrial gas turbines.* Figure 3-34 gives the distribution

*Leopold, J., “Erfahrungen Mit Stationaren Gasturbinen Moderner Bauart,” Der. Mascliinrtischarlen,
Vol. 53, No. 5, 1980.