SKF Reliability Systems - Library

Vol 23 No 3 AMMJ
The costs of implementing the step changes required for this case study are not presented in this paper.
Costs will depend on the strategy used to introduce the required changes and the timeframe over which the
change must be achieved. Costs to consider include labour (internal and external resources), expenses
(travel and accommodation, training, software and hardware, equipment modifications) and any performance
fees/incentives/rewards used to motivate success.
CONCLUSIONS
The use of an Asset Productivity Index (API) has proven to be practical and effective as an overall measure of
a businesses performance in achieving productivity from its physical assets. Unlike traditional benchmarking
approaches, the API provides diagnostic insight into the work processes that require improving enabling an
improvement plan to be developed from the results of the study.
The mix of process and results metrics allows an improvement plan to be developed incorporating metrics with
a logical time sequenced relationship that recognises that results metrics take time to respond to the improved
processes implemented during a step change improvement program.
ACKNOWLEDGEMENTS
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An API In Benchmarking Assets
The author wishes to acknowledge his colleagues in Fluor’s Greenville South Carolina office who have
developed and tested the API suite of metrics on assessment projects worldwide for both client performed
maintenance operations and Fluor performed maintenance projects.
REFERENCES
1 Humphries, James B & Cunic, Bradley K 2004, ‘Improving Asset Performance: A Maintenance Road Map’,
Chemical Engineering, August 2004, Reprint.
2 Fluor O&M API Homepage, viewed 21 March 2009,
Technical Short Feature:
Electrical Damage to Rolling Element Bearings
Electrical damage to rolling element bearings is a common cause of failure - common
enough to have a whole category listed under the ISO standard for Bearing Damage
(ISO 15243:2004, from www.iso.org) It’s technically called electrical erosion. So where
does the damage come from, and what can you do to prevent it from happening in your
machines?
There are basically four cases to consider: Is the machine moving or not; and are you
getting current leakage, or a high amperage discharge through the bearings?
Electrical current passage through bearings can happen when machines are not
moving. Example: your friendly contractor does some welding at your plant and decides
to attach her ground via your nearby electric motor. This would be a high amperage
discharge, and might “weld” bearing parts together internally. Low intensity current
would likely produce many tiny craters that aggregate into darker areas of damage. If
you have burnt-smelling lubricant as well, it’s another confirmation of current leakage. This leakage might be
from static discharge (are you making plastic or paper products?) or from high voltage current spikes caused
by variable frequency drive (VFD) converters.
When the machine is moving, the current passage often produces a very regular pattern of fine, dark lines
across the bearing raceway. These can grow in size and depth as the damage continues. If you don’t have
vibration monitoring, eventually an operator will hear it, hopefully before something catastrophic happens.
What can be done to eliminate these unwanted currents? If you suspect static discharge, inspect your
grounding: straps get corroded or come loose. If you suspect VFD’s as the source, have an expert look at
your cabling, especially cable quality, lengths and termination.
Some motors and generator sets simply produce stray currents that can’t be eliminated. In these cases,
change to a bearing with Insulation (SKF Insocoat, for example) or a bearing with ceramic rolling elements to
allow the current to go safely to ground. Whatever you’d pay for these parts is a small cost considering the
price of your downtime. Content and pictures courtesy of SKF @ptitude Exchange