PERFORMANCE LOSS INVESTIGATION USING THERMAL IMAGING

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PERFORMANCE LOSS INVESTIGATION USING THERMAL IMAGING
283
PERFORMANCE LOSS INVESTIGATION USING THERMAL IMAGING
PRESENTER AND AUTHOR:
SCOTT MCPHERSON
LEAD FIELD ENGINEER – SULZER PUMPS (US) INC
Tel: 281 417 7109
E-MAIL: [email protected]
ABSTRACT
An axially split, opposed impeller, high speed water injection pump ran well for several months.
Head, capacity and efficiency started to degrade markedly, but the pump turned freely and was
relatively smooth. It was disassembled and inspected. All the wear parts, impellers, casing and
other components were in like new condition. The impellers were underfiled and the pump
returned to service - with the same unacceptable performance results. A thermal image camera
was used to check for hot or cold spots and those images will be presented. The detected
hotspot resulted in a bore scope inspection of the cross over passage, and uncovered the
cause of the performance problem.
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PROBLEM SYNOPSIS
•
High speed high pressure water flood injection pump was reported to be
severely underperforming.
•
Pump is an API BB3, 13 stage
•
Pump rated for 410 usgpm @ 10,000ft @ 5400rpm.
•
Pump is variable speed via VFD drive
•
Initial reservoir pressure requirements resulted in initial pump operation
at only 3600rpm
•
As reservoir pressure increased, pump speed was increased to meet
increased pressure demand
•
Low performance was only noticed after approximately 10 months
operation, when pump speed approached rated speed and was found to
be low on pressure
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FIELD PERFORMANCE TESTING
•
Field performance testing
was utilized to assess
underperformance
•
Flowrate obtained using an
ultrasonic flowmeter
attached to the suction line
•
Developed head obtained
utilizing field pressure
gauges and converting to
head based on estimated
specific gravity of the
produced water
•
Dual traverse flow cells installed on the suction and balance line
leak-off piping
Pump absorbed power estimated from motor voltage and amp loads
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loss. Head low by
approximately 20%!!!
•
100
18000
90
16000
80
14000
70
12000
HEAD CAPACITY
60
09 EFF
10000
50
8000
40
6000
09 TDH
EFFICIENCY
30
4000
20
2000
10
0
Efficiency down by
0
0
100
200
300
400
500
600
700
800
2000
approximately 30%!!!
Efficiency
severe performance
20000
200
1900
180
09 BHP
1800
160
1700
140
1600
120
1500
100
1400
80
BHP SG
1300
0.9931
60
NPSHR
1200
40
1100
20
1000
0
0
100
All data adjusted to
5432 RPM
200
300
400
500
600
700
800
Gallons Per Minute
Measured Avg Speed
Brake Horsepower Adjusted to
5432 RPM
Specific Wt
0.9931
g/cm³
4
NPSHR (Feet)
Field testing suggested
Brake Horsepower (BHP)
•
Total Developed Head (Feet)
PERFORMANCE
287
FIELD VIBRATION READINGS
•
•
0.24
Route Spectrum
25-Sep-09 12:14:20
OVERALL= .2432 V-DG
PK = .2424
LOAD = 100.0
RPM = 5486. (91.44 Hz)
Suction 4X running speed
vane pass pressure
pulsations
1.00
0.18
5.00
0.12
0.06
0
No readings more than
0.24 in/s overall
All spectrum
characteristics were
explainable and typical
of normal pump
operation
4.00
0.30
P K V elocity in In/Sec
Vibration spectrums
showed no
abnormalities that
could explain
performance loss.
0
Acceleration in G -s
•
WF4 - WF04 Pump D
WF04 PMP A-POH Pump Outboard Horizontal
3
6
9
12
Frequencyin Orders
15
18
21
Route Waveform
25-Sep-09 12:14:20
RMS = 1.32
PK(+/-) = 3.50/3.93
CRESTF= 2.98
3
2
1
0
-1
-2
-3
-4
-5
0
1
2
3
Revolution Number
4
5
Ordr: 3.999
Freq: 365.63
Spec: .206
Pump POH spectrum and time waveform indicating the dominance of the
4X suction impeller vane pass pulsations
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INITIAL CORRECTIVE EFFORTS
•
Initial postulations were focused in
internal pump recirculation across the
center bushing, possibly due to wear
or swelling of the pump casing
•
Pump was sent to local service facility
for inspection
•
Sadly, no smoking guns were found
•
High pressure bushings clearances
were all in as shipped condition. No
material loss noted.
•
Wear part lift checks indicated no loss
of material at wear ring clearances.
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INITIAL CORRECTIVE EFFORTS
•
Some precautionary modifications were made, though unlikely to resolve
entire problem
•
Impeller underfile added to all impeller discharge vanes
•
Case crown added to force improved sealing of the pump split line. One
possible cause thought to be swelling of casing at high pressure. Could
be a problem that arises with increased speed
•
Top and bottom half casing matching reviewed and refined
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RESULTS AFTER INITIAL MODIFICATIONS
•
No improvement was observed!!
•
Pressure gauge added to pump
discharge nozzle. Reading compared
well to gauge on discharge line
•
Pressure gauge was added to a vent
on the long cross over with interesting
results!!!!
•
Suction side of pump found to be
performing as expected
•
All losses isolated to the discharge
side of pump
•
Pump run down at 3600rpm to allow
comparison to factory performance
test results. Pump still 20% low at
factory test speed!!!
•
Further investigation was required
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TROUBLE SHOOTING FOR POSSIBLE CAUSES
•
Further investigation of pump performance history was carried out. DCS
archives researched to identify when performance loss occurred
•
Investigation revealed that the pump did perform according to the factory
performance curve during first months of operation
•
Performance slowly degraded with time
CONCLUSIONS (or not)
•
Problem seemed to be located at high pressure side of pump
•
Degradation with time could be caused by foreign debris build up, but no
build up noticed during recent shop inspection?????
•
Degradation with time could be caused by excessive wear, but no wear
was observed during recent shop inspection?????
•
What do to next?????
•
Generally speaking, energy losses translate to temperature rise.
Why not try looking at the pump with a thermal image camera?
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THERMAL IMAGING
Bottom half of pump was found to be
warmer than the top half
Zoning in
No exceptionally high localized hot spots apparent,
however, left of thermowell boss appears cooler
Definite relative difference across
thermowell
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BORESCOPE INSPECTION
•
Borescope with articulating head was utilized to perform internal pump
inspection in the field.
•
Camera fed through drain point on bottom half long crossover
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BORESCOPE INSPECTION
Outlet of long cross over
inspected first for obstruction.
Nothing found.
Outlet of long cross over inspected first
for obstruction. Nothing found. But what
is that we see in the distance?
A BIG HOLE!
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EXPLANATION OF FINDINGS
•
Last 7 stages recirculating
additional flow due to 1 inch
hole from discharge to
cross over
•
7 stages worth of
differential pressure across
1 in hole = lots of flow
•
Excessive temperature rise
due to fluid recirculation
passing through 7 stages x
2!!
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REPAIR PROCESS
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ROOT CAUSE
•
CHAPLETS (SHOWN BELOW) ARE USED
TO POSITION SAND CORE BOXES
DURING THE CASE CASTING PROCESS.
•
THE CHAPLETS SHOULD BE MADE OF
THE SAME MATERIAL AS THE CASTING
AND IS INTENDED TO FUSE INTO THE
CASTING AND BECOME A PART OF THE
FINISHED COMPONENT
•
IN THIS CASE IT APPEARS THAT THE
CHAPLET MAY HAVE NOT FUSED, OR
POSSIBLY BEEN MADE OF THE WRONG
MATERIAL
•
NOTICE THE SQUARE RECESS AROUND
THE HOLE FOUND IN THE CROSS OVER
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