The document discusses condition monitoring techniques for various industrial machines, including vibration analysis, enthalpy-entropy plots, and performance testing. It provides examples of how analyzing vibration spectra, efficiency parameters, and test results helped diagnose issues like bearing instability, steam leakage, and internal pump wear. Catching problems early through condition monitoring techniques can help minimize downtime and reduce operating costs.

1. “If it ain’t broke, don’t fix it”
Ray’s Big 5 CM wins – stories where
condition monitoring paid off big time!

2. Vibration analysis- the main CM
technique
Diagnosing causes of vibration
Amplitude
Direction (H, V, A)
Frequency
Phase of 1X vibration
…and how these vary with operating conditions
(speed, load, etc.)
…use diagnosis charts to find likely cause/s. (Even an
iPhone App)

3. REDUCTION AT
SOURCE
Balancing
Balance magnetic forces
(motors)
Fix clearances or
looseness
Reduce aerodynamic
effects REDUCTION OF
RESPONSE
Change natural frequency
of structure:
Add (or reduce) mass
Change stiffness
Increase damping
Detune with dynamic
vibration absorber
ISOLATION
Isolate the source
Isolate affected equipment
m
k
f 
Control of vibration

4. 23/12/2015
Hydraulic power
pack: motor
bearing failures
Vibration analysed
to get spectrum

5. Vibration
velocity –
log scale
Motor: 2970
r/min
5 piston
swash plate
pump
Peak vibration 45
mm/s rms !!!
at 2970 r/min

6. Vibration at
10X from
piston
strokes:
unchanged
Vibration at
2X from
misalignment
: unchanged
After motor-pump
base beam stiffened
Overall vibration
only 5 mm/s rms,
with 1.5 mm/s rms
at 2970 r/min

7. The 5MW fan that was different
Motor 24t, 4m
above ground
level

9. 4 fans: but only this one had very high
vibration @ 1X (738 r/min, or 12.3 Hz)

10. Bearing structure stiffened with
vertical tie bolts. Vibration reduced
80%
But, vibration again increased – motor
was moved 2.5mm axially to get rotor
on its magnetic centre
So, mass was added….

11. Again, vibration was just acceptable
Masses up to 5t added to de-tune system

12. …
Soil checked: OK
(possible that
underground
water affected
foundation
stiffness)
Bearing sliding
supports
modified.
Vibration
increased
steadily- then
bearing failed.
Major off-line
investigation

13. Modal analysis

14. 23/12/2015
Bearing vibration only 2.3 mm/s.
Fan has run OK since.

15. Steam turbines
– still the
mainstay of
power
production
350MW
23MW
500MW

17. Overall condition indicator:
Valves Wide Open test
• Control valves WIDE open
• Steady conditions
• May need to reduce inlet steam pressure
• Test readings: key temperatures, pressures, MW (or
panel instruments if proven)
• No special test flow measurements
• MW output adjusted for
variations from rated values.

18. Test data TEST A Correctn
factor
TEST
B
Correctn
factor
Generator Output MW 355.8 349.7
Steam Pressure - Main kPa 12155 1.02285 12255 1.02053
Steam Temperature - Main °C 529.5 0.99832 526.7 0.99773
Steam Temperature - Reheat °C 525.8 1.0101 539.5 0.99873
Reheater Pressure Drop % 6.76 0.99814 6.03 0.99633
Condenser Pressure - kPa 9.34 1.01225 12.44 1.03615
Generator Power Factor 0.923 1.00012 0.945 1.00064
Steam Temp. Cont. Spray - Main kg/s 6.5 0.99889 24.6 0.99584
Steam Temp. Control Spray - Reheater
kg/s
0 1 0 1
Final Feedwater Temperature °C 234.9 1.0005 230.5 0.98957
Combined correction factor 1.04741
Corrected VWO Output MW 372.7
Unit had a record run of 6
months continuous on line
service….

19. Test data TEST A Correctn
factor
TEST
B
Correctn
factor
Generator Output MW 355.8 349.7
Steam Pressure - Main kPa 12155 1.02285 12255 1.02053
Steam Temperature - Main °C 529.5 0.99832 526.7 0.99773
Steam Temperature - Reheat °C 525.8 1.0101 539.5 0.99873
Reheater Pressure Drop % 6.76 0.99814 6.03 0.99633
Condenser Pressure - kPa 9.34 1.01225 12.44 1.03615
Generator Power Factor 0.923 1.00012 0.945 1.00064
Steam Temp. Cont. Spray - Main kg/s 6.5 0.99889 24.6 0.99584
Steam Temp. Control Spray - Reheater
kg/s
0 1 0 1
Final Feedwater Temperature °C 234.9 1.0005 230.5 0.98957
Combined correction factor 1.04741 1.03521
Corrected VWO Output MW 372.7 362

20. Enthalpy
Drop
Efficiency
P1
T1
P2
T2
T3
P3
Expansion line
Enthalpy
Entropy kJ/kg °K
kJ/kg
Isentropic
enthalpy
drop
Actual
h drop
Ideal
h drop
Actual h drop
Ideal h drop
Usually 85–
90%.
Lowers with
damage or
blade deposits.
Enthalpy, entropy
from temperature
and pressure.

21. -4
-3
-2
-1
0
1
2
3
4
5
6
0 1000 2000 3000 4000 5000 6000 7000 8000
VWO
IP effy
IP PR
% Deviation in CM parameters with hours in service
350MW reheat unit – 3 casings
Blading stages: 8 HP, 6 IP, 6 LP.
Steam forced
cool run @
7400h
Pressure
Ratio
Inlet/Outlet
also handy

22. IP Blading

23. 500MW
HP, IP, 2 x LP
Other use of enthalpy/entropy plot

25. Symptom: burnt paint on an LP
hood
Temperature well above usual 40 degC = internal leakage of
hot steam into exhaust space
Likely cause: failure of outer bellows in steam inlet piping.
Pieces of bellows found inside condenser, so temporary repair
Outer bellows
leak - into LP
hood

26. P1
T1
P2
T 3P3
Expansion line
Enthalpy
Entropy kJ/kg K
kJ/kg
Isentropic
enthalpy
drop
Saturated steam zone
A
T2
Temperature usually at
saturation - if greater, steam
is superheated, has
bypassed blading.
THEN …..255 °C
steam inlet noticed
in LP2 feedwater
heater piping - 95 °C
is usual

27. Expansion
bellows
failures.
914mm diameter,
two sets in each
of 4 pipes.

28. Another type 500MW unit. VWO Output from
DCS trend close to special tests
VWO from plant
instruments
VWO using special
test instruments
R

29. Inlet strainer and blading
blockage –turbine
troubles detectable
by performance analysis

30. Massive turbine vibration
HP
P
LP
Generator 3000 r/min
Gearbox and
Exciter
Journal bearings
Coupling
120MW steam
turbine
generator, 17
years’ service
Generator
was balanced
in situ: novel
method.
On return to
service,
vibration went
off scale!

31. Generator balancing had been done - with boiler off
line!
Coupling
disconnected
Exciter
wired to
run as
motor
Rope
wrapped
around
rotor, to
overhead
crane to
overcome
initial
inertia
When
rolling,
exciter (i.e.
“motor”)
switched
on, raised
rotor to
3000 r/min
for
balancing
runs

32. Jacking oil supplied
at bottom to lift
rotor, reduce start-
up friction
Pump is stopped
when machine
> 600 r/min.
Local pressure gauges
now read the oil film
“wedge” pressure –
proportional to load

33. Vibration on return to service ..!!!
All OK...until
speed reached
about 2950
r/min
Generator
vibration
increased
suddenly, got so
great that turbine
was shut down Starting up
tried again but
problem
remained
Vibration
analysis
instruments
installed

34. 0 20 50
Vibration frequency Hz
Vibration
velocity
Vibration
increasing @
19.5Hz
19.5 Hz (1190 r/min) is the First Critical
Speed of the generator rotor…
Vibration transducers installed, analyser on PEAK HOLD, turbine started up

35. The turbine is synchronised and loaded OK
Vibration started when
Auxiliary Oil Pump was
stopped (Main Oil Pump
on the rotor line takes
over at near 3000 r/min).
19.5Hz vibration still
present, could be
increased and
decreased by varying
cooling water flow to
oil coolers.
Aux pump was left
in service, and the
turbine loaded
without high
vibration.
Pump was
stopped with no
effect (phew!).

36. The facts
• Bearing stability? - Available references searched
– Cause: “Resonant Whirl”
– Solution: “modify bearing”
BUT…. “Turbine has been in service for
17 years with no problem!”
Vibration at
frequency of
1st Critical
Speed, while
rotating > 2X
this speed
A trigger -
sudden drop in
pressure of oil
supplied to
bearings when
Auxiliary Oil
Pump stopped
(125kPa to
70kPa)
Changing
oil
temperature
(i.e. its
viscosity)
altered
vibration

37. ESDU
66023
Engineering Sciences
Data Unit (IMechE, UK)
2
/







d
c
Nbd
W
W d
e

38. Symbol Description Details Data
W Load on the
bearing
Rotor mass is 32072 kg.
With a semi-flexible
coupling, it should be
evenly shared between
the two bearings.
….confirmed: wedge
pressure readings
similar at 200 kPa
157313N
2
/







d
c
Nbd
W
W d
e

39. Symbol Description Details Data
e Dynamic
viscosity of oil
in the bearing
Heavy grade turbine oil
(VG 68).
Oil draining from the
bearing is close to the
average temperature in the
bearing. Control Room
instruments used.
Temperatures varied
between 40°C and 71°C.
64 × 10-3
N.s/m² @
40°C;
13× 10-3
N.s/m² @
71°C
2
/







d
c
Nbd
W
W d
e

40. Symbol Description Details Data
N Rotational
speed
Full speed was used 50rev/s
b Length of
bearing
Measured on bearing 0.392m
2
/







d
c
Nbd
W
W d
e

41. Symbol Description Details Data
d Diameter of
bearing
From plant data –
the journal diameter
(b/d = 1.03)
0.381m
cd Diametral
clearance –
bearing to
journal
Measured at the
maintenance
outage.
0.406 mm
to
0.686 mm
2
/







d
c
Nbd
W
W d
e

42. Sommerfeld Number
Load parameter W’
0.1
1.0
10
0.1 0.5 0.9
Eccentricity ratio
Oil 71°C
Oil 40°C
Increased risk of half-
frequency whirl
Original
operation
Operation
when
bearings
modified
Recommended
area
Lines of
increasing
constant b/d
Bearing
too short
ESDU66023
plot
2
/







d
c
Nbd
W
W d
e
Operating
points
calculated,
plotted

43. Bearing instability can occur!
Recommended:
shorten bearing - to
same b/d ratio as newer
turbine of same make.
Differences found
between spare parts,
plant drawings!
Adjacent twin machine
found to have short
bearings!
• Bearings shortened -
machine returned to
service
• Vibration problem solved
• …. 1st Critical Speed
was higher - 1320 r/min.

44. World’s most
common machine
(after motors)
Use 25% of
world’s total
motor-driven
electricity,
….or about 6.5%
of global
electricity
production!!
Pumps

45. Erosion of
impeller

46. Sealing
rings
Ring section diffuser
pump
Internal
leakage
Increased clearance
increases recirculation
Erosion at
sealing rings

47. Pump internal wear
Head
H
Flow Q
Internal leakage
recirculation
H-Q with wear

48. Pump internal wear
0
5
10
15
20
0 500 1000 1500
Days in service
%Reductioninhead
230kW Cooling water pump
degradation
Increasing internal
leakage reduces
Head at chosen
datum flow

49. Close to linear for 4500kW pump, too
y = -0.155x2 + 0.4907x - 0.1388
-12
-10
-8
-6
-4
-2
0
2
0 1 2 3 4 5 6 7 8 9 10
%reductioninHead@datum
flow
Time: years since overhaul
Boiler Feed Pump wear trend

50. Effect of increased internal wear in
relates to Specific Speed:
Using data at Best Efficiency Point:
N = Rotation speed, r/min
Q = flow per impeller eye, m³/h
H = head per stage, m
(Number resulting is close that from
US units)
75.0H
QN
Ns 

52. 0
2
4
6
8
10
12
14
16
18
20
0 1000 2000 3000 4000 5000
Specific Speed (US units)
% Increase in
power
Clearances worn to 2X
design
Clearances worn to
1.5X design

53. Head-Flow method for CM
At around normal duty point is enough.
Checks condition of pump AND its system.
Repeatable pressure and flow measurement needed,
and speed for variable speed pumps.

54. Optimum time for overhaul - on energy
saving basis (1)
1 Pump wear causes
drop in plant production
2 Pump duty is
intermittent to meet
demand
• Overhaul readily
justified
• Wear means extra
service time and extra
energy

55. Optimum time for overhaul - on energy
saving basis (2)
3 Pump wear does not
affect plant production, at
least initially.
Constant speed,
output controlled by
throttling – monitor control
valve position
4 Pump wear does not
affect plant production, at
least initially.
Output controlled by
varying speed –monitor
pump speed
•Same basic method applies...

56. An example-
Boiler Feed
Pump in PS
Pump overhaul
cost - $50 000
Cost of power
3c/kWh
Pump runs for
90% of time on
average Tested at 24
months since last
overhaul

58. Extra power
used = 2300
– 2150 =
150kW
÷ motor
efficiency to get
extra power
consumed by
motor/pump
combined… = 167kW
Extra power cost: (720h is average
month) =
167 × 0.03 × 0.90 × 720
kW $ % h
= $3246/month

59. The average cost
rate of deterioration:
$ 3246 ÷ 24 =
$135 /month/month
The optimum time for
overhaul:
= 27.2 months
C
O
T
2

Total cost curve
often fairly flat
around the
optimum

60. The method does not apply to all
pumps…..
Small pumps may cost more to test
than overhaul, energy costs too small
to justify work?
Pumps of Specific Speed above 2000
have flat or declining Power-Flow
curve, so increased leakage does not
use more power

61. Conclusions
Condition
monitoring is an
exciting activity
with big benefits
CM is much
more than
vibration analysis Performance
analysis adds the
energy-saving
dimension -
USE IT

62. raybeebemcm@gmail.com
FedUni programs in Maintenance and Reliability Engineering:
on-line distance learning (open to all: conditions apply) (were
Monash Uni)
Happy Monitoring !