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Slide 1
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
EPRI TR-1010792
MECHANICAL SERIES
MODULE 14
CENTRIFUGAL PUMP VIBRATION
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Slide 2
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
MODULE OBJECTIVES
Describe types of pumps and their
typical applications
Define/Describe:
-Pump Curves
-Best Efficiency Point
-Head vs. Resistance
-How to Use Performance TestingData to Monitor Pump InternalClearance Degradation
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Slide 3
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
MODULE OBJECTIVES
Present Basic Vibration Theory
Present Simple Vibration Calculations
Define/Describe Typical Pump Failure
Modes
Describe Standard Vibration
Monitoring, Analysis, and Diagnostics
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Slide 4
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
SINGLE VOLUTE PUMP
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Slide 5
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
DOUBLE VOLUTE PUMP
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Slide 6
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
DIFFUSER PUMP
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Slide 7
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
IMPELLER CONFIGURATIONS
Enclosed Semi-Enclosed Open
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Slide 8
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
SINGLE SUCTION IMPELLER
ImpellerDiameter
Wear Ring Hub
Suction Vane Edge
Shroud
Discharge Vane
Edge or Tip
EyeDiameter
Suction Eye
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Slide 9
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
DOUBLE SUCTION IMPELLER
ImpellerDiameter
EyeDiameter
Wear Ring Hub
Suction Eye
Suction Vane Edge
Shroud
Discharge Vane
Edge or Tip
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Slide 10
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
PUMP AND HEAD TERMINOLOGY
Head - used as a measure of energy and has the units of feet.
Friction head(hf)- the energy required to overcome resistance
to flow in the pipe, fittings, valves, entrances and exits.
Velocity head(hv)- the energy of a fluid as a result of its
kinetic energy.
Pressure head(hp)- the pressure of the fluid being pumped.
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Slide 11
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
PUMP AND HEAD TERMINOLOGY
Static suction head(hs)- the vertical distance in feet above thecenterline of the pump inlet to the free level of the fluid source. If
the free level of the fluid source is below the pump inlet, hswill be
negative and is referred to asstatic suction lift.
Static discharge head(hd)- the vertical distance in feet above thepump centerline to the free level of the discharge tank.
Net suction head(Hs)- the total energy of the fluid entering the
pump inlet. It includes thestatic suction head (hs), plus the
pressure head(if any) in the suction tank (hp
), plus the suction
velocity head (hv), minus the friction head (hf)in the suction piping.
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Slide 12
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
NET SUCTION HEAD
Net suction head(Hs)- the total energy of the fluid entering thepump inlet. It includes thestatic suction head (hs), plus the
pressure head(if any) in the suction tank (hp), plus the suction
velocity head (hv), minus the friction head (hf)in the suction piping.
p, hp
hs
hf
h
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Slide 13
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
PUMP AND HEAD TERMINOLOGY
Net discharge head(Hd)- the total energy of the fluid leaving the
pump. It includes the static discharge head (hd), plus the dischargevelocity head (hv), plus the friction head in the discharge piping
(hv), plus the pressure head (if any) in the discharge tank (hp).
p, hp
hdhf
h
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Slide 14
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
PUMP AND HEAD TERMINOLOGY
Total dynamic head(H) - the net discharge head minus
the net suction head. The total amount of energy added
to the fluid by the pump.
H = Hd- Hs
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Slide 15
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
PUMP AND HEAD TERMINOLOGY
Net positive suction head required(NPSHR)- the minimum fluid
energy required at the inlet to the pump for satisfactory operation.
Net positive suction head available(NPSHA)- the fluid energy at
the inlet to the pump above the fluids vapor pressure.
Cavitation- the vaporization of the
fluid within the casing or suction line.
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Slide 16
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
INTEGRATED CURVE
4000
HEA
D(ft)
3500
3000
20002500
FLOW (gpm)
0 100 200 300 400 500 600 700
100
90
80
70
60
50
40
30
20
10
0
Eff. %60
4020
0
600
400
200
0
PSHR(ft)
BHP
PSHR
Head
EFF %
BHP@ 1.0 Specific Gravity
Typical Auxiliary Feedwater Pump Curves
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Slide 17
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
ESTIMATING PUMP INTERNAL
CLEARANCE DEGRADATION
1.Using Performance Test Data to Calculate % Head Loss at the
Operating Conditions
2.Using a Balance L ine DP Correlation to I nternal Clearance Status
3. Performing a Static Rotor L if t Check and Measur ing Clearances as
Close as Possible to the Wear Rings
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Slide 18
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
BASIC VIBRATION THEORY
m
a
F
maFNewtons Second Law = Dynamic Equation of Motion
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Slide 19
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
SINGLE DEGREE OF FREEDOM SYSTEM
kc
mx(t)
F(t)
kx
F(t)
m x
xmxckxtFF )( )(tFkxxcxm
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Slide 20
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
FREE VIBRATIONS
Time
Amplitude
e n t
sin( ) d t
)sin()( tAetx d
t
cn
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Slide 21
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
FREE VIBRATIONS
m
kn
21 nd
km
c
c
c
cr 2
Natural Frequency of
Undamped System in rad/sec
Damping Factor
Natural Frequency of Damped
System in rad/sec
Period of Oscillations in sec
f = Frequency in HzfT
d
12
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Slide 22
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
APPLICATION
x0
x1
x2x3
x4
d t
d t0 d t1 d t2 d t3 d t4
pi
i
x
x
p ln
2
1
ipi
dtt
p
2
21
dn
2
nmk
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Slide 23
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
FORCED VIBRATIONS
)cos()( tXtx
)()sin()( txtXdtdxtx
)()cos()( 22 txtXdtxdtx
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Slide 24
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
FORCED VIBRATIONS
fT
12
)cos()( tXtx
0RXX
kFX 00
222 )2()1(
1)(
rr
rR
2
1
1
2tan)(
r
rr
n
r
with
Time t
x(t)
X
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Slide 25
EPRI PSE
Mechanical, Module 14-Centrifugal Pump Vibration
FORCED VIBRATIONS
0
0 1,
0 2,
0 3,
0 6,
1
0 1.0 2.0
0.1
1.0
10.
100.
R
r
Dynamic amplification factor R r( ) as a function of
(Logarithmic scale)
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Slide 26
Mechanical, Module 14-Centrifugal Pump Vibration
FORCED VIBRATIONS
( )r
0
0 01,
0 1,
0 2, 0 6,
1
0.0 1.0 2.0
0
40
80
120
160
r
180
Phase angle ( )r as a function of
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Slide 27
Mechanical, Module 14-Centrifugal Pump Vibration
PRACTICAL APPLICATIONS
Following is a presentation of practical methods
for the determination of system dynamic characteristics
from vibration plots. We are interested in calculating:
Damping factors
Natural Frequencies
Critical speeds
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Slide 28
Mechanical, Module 14-Centrifugal Pump Vibration
PRACTICAL APPLICATIONS
Rmax
Rmax
2
r1
r2
0. 1. 2. 3.r
R
r
dB
n
r
2
1
2
1
Plot of Pump Bearing Vibration Amplitude
as a Function of Excitation Frequency
nFor r = 1
Critical Speed fNcr 60 , RPM
2
nf , Hz
, rad/sec
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Slide 29
Mechanical, Module 14-Centrifugal Pump Vibration
PRACTICAL APPLICATIONS
X3
X2
X1
N1 N2 N3N rpm
X Vibration Amplitudes Provide an Easy and Fairly Accurate
Method of Determining Critical Speeds from Bode Plots
n
Damping Factor
Natural Frequency
2
n
f
, rad/sec
, Hz
Critical Speed fNcr 60 , RPM
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Slide 30
Mechanical, Module 14-Centrifugal Pump Vibration
PRACTICAL APPLICATIONS
Using Phase Angle Measurements(Not Very Ac cu rate due to Uncertaint ies o f
An gle Measurements)
n
Damping Factor
Natural Frequency
( )r
2
1
N1 N20.
0
40
80
120
160
N rpm
180
2
nf
, rad/sec
, Hz
Critical Speed fNcr 60 , RPM
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Slide 31
Mechanical, Module 14-Centrifugal Pump Vibration
SIMPLE ROTOR HAVING 2 CRITICAL SPEEDS
DUE TO DISSIMILAR SUPPORT STIFFNESS
PO G x
y
z
t
O
P
G
e
u
y
xx
y
e1
e2
MKxnx
M
Kyny
nx
xr
ny
yr
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Slide 32
Mechanical, Module 14-Centrifugal Pump Vibration
SIMPLE ROTOR
X
e,Y
e 0 180 360
rx 1 ry 1 r rx y,
0.
1.
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Slide 33
Mechanical, Module 14-Centrifugal Pump Vibration
PUMP FAILURE MODES
Loading ResponseStatic forces and moments on the casing:
- Impeller radial thrust (primary static load of
the rotor)
- Weight of the rotating assembly
- Static loading varying with pump flow rate
- Static bearing and seal forces
- Static shaft deflection
- Rotor axial position movement
Dynamic forces and moments fixed on therotor:
- Impeller hydraulic unbalance (primary
dynamic load of the rotor)
- Rotor mechanical unbalance (secondary
dynamic load of the rotor)
- Dynamic bearing and seal forces
expressed as vibrations
Dynamic instability mechanisms:
- Pump bearing whirl
- Rubs
- Impeller vane pass
- Rotor eccentricity
Multiples and sub-multiples of running
speed from analysis:
- Sub-synchronous frequencies
- Impact
- Multiples of running speed
Pump Loading and Associated Response
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Slide 34
Mechanical, Module 14-Centrifugal Pump Vibration
PUMP FAILURE MODES
Loading Response
Static:
- Nozzle loads
- Foot loads
Static structural response is not currently
measuredDynamic:
- Seismic nozzle loading- Seismic foot loading
Dynamic structural response:
- Seismic response not recorded- Natural frequencies usually
accounted for
- Running speed components
- Sub-harmonics analyzed
Structural L oading and Associated Response
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M d l 14 C if l P Vib i
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Slide 35
Mechanical, Module 14-Centrifugal Pump Vibration
PUMP FAILURE MODES
Loading Response
- Bearing and seal static and dynamic
loading- Flow induced loading
Mostly pressure, temperature and flow
measurements and performance trending
Operational Loading and Associated Response
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Slide 36
Mechanical, Module 14-Centrifugal Pump Vibration
BASIC VIBRATION DIAGNOSTIC TECHNIQUES
Vibration Measurements
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M h i l M d l 14 C t if l P Vib ti
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Slide 37
Mechanical, Module 14-Centrifugal Pump Vibration
BASIC VIBRATION DIAGNOSTIC TECHNIQUES
Vibration Measurements
Shaft
Bearing
Casing
MotorVertical
Accelerometer
Axial
Accelerometer
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Mechanical M d l 14 C t if l P Vib ti
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Slide 38
Mechanical, Module 14-Centrifugal Pump Vibration
BASIC VIBRATION DIAGNOSTIC TECHNIQUES
Vibration Sensors
Moving Object: (Shaft)
Fixed Object
(Bearing)
Displacement
Probe
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Slide 39
Mechanical, Module 14-Centrifugal Pump Vibration
BASIC VIBRATION DIAGNOSTIC TECHNIQUES
Vibration Sensors
Transducer Case
Vibrating Mass
Piezoelectric Element
(Spring)
Transducer Mount
Transducer
Wiring
Integrated
Electronics
Magnetic Base
Support Element
Piezoelectric Accelerometer
Transducer Case
Coil
Damper (oil)
Vibrating Mass
Stiffness Element
(Spring)
Permanent Magnet
Transducer Mount
Transducer Wiring
Seismic Velocity Transducer
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Slide 40
Mechanical, Module 14-Centrifugal Pump Vibration
BASIC VIBRATION DIAGNOSTIC TECHNIQUES
Vibration Acceptance Criter ia
Recommended Limi ts for Overall Casing Velocity
Peak Velocity Acceptance Class
Less than 0.15 ips (3.8 mm/sec) Acceptable
0.15 to 0.25 ips (3.8 6.3 mm/sec) Tolerable
0.25 to 0.4 ips (6.3 10 mm/sec)May be tolerable for moderate periods of
time. Monitor closely to warn of changes0.4 to 0.6 ips (10 15 mm/sec)
Impending failure; watch closely for changes
and be prepared to shut down for repairs
Above 0.6 ips (15 mm/sec) Danger of immediate failure
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Slide 41
Mechanical, Module 14-Centrifugal Pump Vibration
BASIC VIBRATION DIAGNOSTIC TECHNIQUES
Vibration Acceptance Criter ia
Recommended Limits for Shaft Vibration
- API and AGMA specify that, for the purpose of acceptance, maximum shaft
amplitude peak-to-peak expressed in mils shall not exceedRPM
000,12 or 2 mils
whichever is less.
- In this criterion, shaft motion includes runout, which can be no more than25% of the allowable displacement.
- This guideline is established for new machinery; operating machinery cantolerate higher levels.
- Consult OEM
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Slide 42
Mechanical, Module 14-Centrifugal Pump Vibration
BASIC VIBRATION DIAGNOSTIC TECHNIQUES
I nterpretation of Vibration Spectra
Cause Frequency Amplitude Phase NotesUnbalance 1 x RPM Proportional to
unbalance Radial
- steady
1 Reference
mark - steady
Most common cause of vibration, no phase
change
Misalign-
ment
(1, 2, 3, ) x
RPM
Axial high 1, 2 or 3
referencemarks
Second most common cause of vibration.
Axial amplitude may be twice the vertical orhorizontal.
Eccentricity 1 x RPM Varies 0 or 180o
between
Horizontal
and Vertical
Balancing may reduce vibration in one
direction but increase it in the other
Bent shaft (1 to 2) x
RPM
Axial - high 180oout of
phase axially
Same radial phase on both bearings Orbit
and phase are good parameters to monitor
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Slide 43
Mechanical, Module 14 Centrifugal Pump Vibration
BASIC VIBRATION DIAGNOSTIC TECHNIQUES
I nterpretation of Vibration Spectra
Cause Frequency Amplitude Phase Notes
Thermal
bow
1 x RPM Varies 1 Reference
mark - steady
Increasing vibration during load variations
and startup from a cold condition
Looseness (1, 1.5, 2, 2.5,
3, ) x RPM
Proportional to
load
2 reference
marks,
slightly
erratic
Frequently coupled with misalignment
Strobe may help. Amplitude depends on
load
Soft foot 1 to 2 x RPM Proportional to
load
Check mountings for variations in amplitude
Electrical 1 x RPM or 1
to 2 x line
frequency
Large Erratic When power is turned off vibrations
disappears instantly
Sleeve
bearings
wear and
clearance
(1, 2, 3, 4, )
x RPM
May be higher in
Vertical than
Horizontal
Erratic Compare shaft to bearing displacement
readings. Oil analysis best monitor for wear
Oil whip .5 x RPM Radial
unsteady,
excessive
Erratic Frequency is near one-half running speed
(machine speed is nearly 2x critical speed)
Oil temperature is a good indicator
Oil whirl (.42 to .48) x
RPM
Radial
unsteady,
sometimes severe
Erratic Caused by unloading of bearing. Tangential
destabilizing force due to lube film in the
direction of rotation adds energy to vibration
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Slide 44
Mechanical, Module 14 Centrifugal Pump Vibration
BASIC VIBRATION DIAGNOSTIC TECHNIQUES
I nterpretation of Vibration Spectra
Cause Frequency Amplitude Phase NotesAnti-friction
bearings
BPFI, BPFO,
BSF, FTF and
Harmonics
Radial - low Erratic Use velocity, acceleration or spike energy
Rubbing (0-0.5)x, 1x,
and higher
harmonics
Erratic Erratic Similar to impact, may excite many system
frequencies
Gears GMF=Z xRPM Radial - low Erratic Use velocity or acceleration. Tooth wear isbetter indicated by side-bands around GMF
and excitation of tooth natural frequency.
Higher tooth load will increase amplitude at
GMF. Backlash is characterized by
decreasing amplitude at GMF when load is
increased. Gear misalignment shows with
higher 2x and 3x GMF. A cracked or broken
tooth is best seen on the time signal. Ahunting tooth problem shows at very low
frequencies
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Slide 45
Mechanical, Module 14 Centrifugal Pump Vibration
BASIC VIBRATION DIAGNOSTIC TECHNIQUES
I nterpretation of Vibration Spectra
Cause Frequency Amplitude Phase NotesFoundation Unsteady Erratic Unstable
reference
Strobe may help
Resonance System
specific
High Erratic Increased levels at resonant frequency. Often
appears on old machines pedestals
Cracks 1x, 2x RPM, Variable during
transients. Drop
in higherharmonics
Phase shift Increased levels at resonant frequency
Phase is a good indicator. 2x RPM
excitation of critical speed during coastdown.
Hydraulic
Forces
Vane Pass =
Z x RPM and
harmonics
High radial and
axial
NA Use velocity or acceleration. Due to uneven
internal gap between rotating vanes and
diffuser. May excite natural frequencies.
Flow obstructions are common causes.
Cavitation Random high
frequency +Vane Pass
High radial and
axial
NA Due mainly to insufficient suction pressure
and the presence of vapor and air in theliquid.
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Slide 46
Mechanical, Module 14 Centrifugal Pump Vibration
VIBRATION SIGNALS EXAMPLES
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Slide 47
, g p
Unbalance
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Slide 48
, g p
Misalignment
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, g p
Vane Pass
5x1x