M a i n t e n a n c e a n d R e l i a b i l i t y
N
o warning or short-
warning failures are the
worst kind. Think of a tire.
It can wear out slowly over thousands of
driving miles or rupture suddenly, at full
highway speed, from a random piece of
road debris. You can monitor tread loss over
time and conveniently schedule a tire
change. Conversely, who could predict the
sudden appearance of a sharp piece of iron?
Fault bubbles are sudden-death condi-
tions in waiting. They haven't ruptured, but
they are about to. Similar to a tire, fault
bubbles can burst instantly. Unlike the tire,
most fault bubbles in industrial machinery
can be revealed by condition monitoring,
which includes the careful examination by
a skilled inspector. Once detected, the root
cause can be arrested or at least mitigated.
In past columns, I've mentioned the P-F
interval. As a review, "P" is the point at
which a failure (in progress) is first
detected, while "F" is the end point of
functional inoperability. Although the P-F
interval is a theoretical concept that has
useful application, it is rarely applied in
real-world machines. This is because the
real world comes with many variable
events. These events distort the predict-
ability of the P-F interval.
Simply stated, the P-F interval is not
well-behaved. It is a time interval that is
influenced by detection skill and frequency.
It is also influenced by multiple operational
factors that determine the failure develop-
ment period. These include:
AS I SEE IT
Jim Fi t ch
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Nori a Corpor at ioN
PROACTIVE
to Avoid Root Cause
FAULT BUBBLES
2
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May - June 2017
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www.machinerylubrication.com
Be