Vibration Analysis – Case Study
In April 2008, a Condition Monitoring regime was introduced to
monitor the health of various critical plant around site. Cooling
water pumps P112 (far) and P113 would be tested monthly
according to duty.
Efftek
Diagnostic Engineers
Vibration Analysis
‘the Efftek way’
Each point on the pump has three different types of radial reading taken
•
•
•
Velocity 0-20 times shaft speed
Acceleration 0-20 kHz (HFB)
Enveloped 0-20 times shaft speed (ESP)
This HFB
The
reading
ESP reading
reading
gives isus
isainformation
the
Highmost
Frequency
important
about Band
balance,
one.
acceleration
It
misalignment
extractsreading
bearing
etc.where
It impact
can we
be
compared
are
information
interested
tofrom
British
in the
resonant
acceleration
Standards
vibration
BS7845
levels
andabove
or
tells
ISO10816
us
about
very3kHz.
accurately
to determine
This if
tells
the
the
usbearing
health
about
of healthy.
lubrication
is
the machine
Again,
condition.
from
no the
ISO
Novibration
orISO
BS or
standard
level.
British
Itiscan
Standards
available
also befor
exist
viewed
thisfor
type
in this
acceleration
of reading.
type of
to give us
reading.
Setting
of some
alarm bearing
limits isinformation
down to experience and is usually 0.5 G’s
Efftek
Diagnostic Engineers
May 2008 – First Readings
The ESP
area
first reading
readings
above 3showed
kHz
on this
showed
a machine
peak very
at around
were
littletaken
252Hz.
activity
in This
May
and proved
it2008.
was
ThebeVelocity
also
to
considered
the bearing’s
reading
satisfactory.
from
outertherace
motor
frequency.
drive endThere
bearingwas
showed
also
amplitudesat of
multiples
2Xless
and than
3X. This
0.5 is
mm/sec
known and
as Harmonic
were considered
activity
satisfactory.
and
is a good indication that there is a problem developing.
The highest peak though was around 40% alarm limit and it
was decided just to keep a close eye on the unit.
Efftek
Diagnostic Engineers
June 2008 – Second Readings
The ESP
velocity
HFB
second
spectra
reading
velocity
plotshowed
converted
showed
spectra
ansome
increase
toshowed
acceleration
small
inno
increased
thesubstantial
fundamental
also did
above
not
increases
3BPFO
show
kHz
and
anything
over
but
was
there
the above
untoward
first
wasone.
thea alarm
and
The
considerable
was
overall
limit.
considered
The
value
increase
harmonic
was
perfectly
1.16mm/sec
below
activity
acceptable.
that
waswhich
value
now
being
wouldswamped
indicating
be classified
bearing
by an
resonance
aselevated
zone B–carpet
(1.12
an indication
–value,
2.8mm/sec
a sure
of asign
- developing
‘Machines
that the
bearing
with vibration
problem.
was in trouble.
within Itthis
waszone
recommended
are normally
that the
considered
bearing
should
acceptable
be changed
for unrestricted
ASAP.
long term operation’ ) under
ISO10816 vibration standards.
Efftek
Diagnostic Engineers
Motor drive end bearing
The motor was removed and sent away for overhaul. The bearing
from the drive end was examined and it was found that it had
suffered from ‘brinelling’ i.e. indentation of the surface of a raceway
by the rolling elements under impact or by static load. These
indentations cover only about one quarter of the surface of the race
indicating that they occurred whilst the pump was on standby, also
suggesting that the pump was always coming to rest in the same
position.
Efftek
Diagnostic Engineers
Motor drive end bearing - closeups
Efftek
Diagnostic Engineers
ESP readings after bearing replacement
The ESP spectras taken in July following bearing replacement
show a reduction to much lower levels.
Efftek
Diagnostic Engineers
Financial Ramifications
In This case, the developing defect was picked up early and only new bearings
were required. The cost was around £1000
However, if the bearing had collapsed then secondary damage could have
occurred and a full rewind and machining of the FLP motor would have been
around £3000
Additionally, had the pump failed, it is highly likely that it would not have been
noticed until a temperature trip occurred and the plant would have been offline an
estimated 12 hours.
Cost savings between £2000 and 12 X £?000 – how much production would you
lose in 12 hours?
Efftek
Diagnostic Engineers