beebe steam turbines cm apr2016 r1
TRANSCRIPT
Steam turbines: some case studies in condition monitoring
Ray Beebe DipMechEng MEngSc FIEAust CPEng(ret)
(28 years in power generation, then 24
years as academic)
Long experience on investigations on
pumps, steam turbines, boilers etc. +
initiatives in condition monitoring
Keen to share – ran training in-house,
wrote handbook
Ray Beebe
Professional engineer/
middle manager
Power Stations etc.
Australia and UK
Monash University
1992 >>
Led Maintenance and
Reliability programs 15
years (postgraduate,
study online)
Conference
papers/speaking – 7
countries
Articles in magazines
worldwide
3 books
“Retired” 2010: now
part-time @Federation
University
RAY’S OPINIONS ON USE OF CM
Asset Condition Monitoring – using data of performance, vibration, inspection, etc. to support maintenance decisions
Turbines are critical plant, well justify application of CM.
Open a turbine only if compelling technical and economic reasons. (High temperature parts get heat affected, may be difficult to dissemble).
OEM advice: consider
Several CM techniques: Vibration analysis and performance analysis most common
Today about performance analysis: three main parameters:
Valves Wide
Open output
Stage
Pressures
and Ratios Expansion
line and
Enthalpy-
Drop
Efficiency
Inlet Control Valves WIDE open, checked
Steady conditions for hour
May need reduced inlet pressure
Test readings (or DCS if proven) of key
temperatures, pressures, MW. No special test
flow measurements
MW are corrected with OEM factors for any
variations from rated terminal conditions.
Valves Wide Open Output: indicator of overall
condition
Parameters:
Corrected stage
pressures (to
standard inlet
conditions)
Pressure ratios,
inlet/outlet
better – not
dependent only
on turbine inlet
pressure value.
…are closely
linear with
flow/load (NOT
Last Stage).
Can use ratios to
detect blockage in
section
Stage
Pressures…
0 Steam flow /Load 100%
EFFECT OF BLADE DEPOSITS, DAMAGE SHOWS
Pressure ratio, inlet to outlet, increases
Effect of
restriction in
section
0 Steam flow /Load 100%
ENTHALPY- ENTROPY CHART (MOLLIER)
A-B-C-D:
Expansion Line
for typical
reheat turbine
E – F:
Expansion Line
for typical non-
reheat turbine
Saturated
(wet) steam
area
(Courtesy Engineering toolbox)
Usually 85–90%.
Lowers with damage or
blade deposits.
Enthalpy, Entropy found from temperature and pressure. Enthalpy Drop Efficiency = Actual Enthalpy Drop Ideal Enthalpy Drop
Enthalpy Drop Efficiency: useful in superheated
zone only
Enthalpy – Entropy diagram -
part of “Mollier” Chart
CASE STUDY A: 200MW (BLADE DEPOSITS)
Usual load 210MW. Steam control valves 90% open
VWO when new: 216MW
Later, operator noticed control valves 100% open
So, VWO test run: 210MW (-6MW )
Planned full Heat Rate test for more diagnostics, but piping
isolations delayed test for 3 months:
VWO was now 216MW
Unit had 11 shutdowns in this time !
Likely problem: deposits on blading,
removed by blade washing effect during
startup/shutdown
CASE STUDY B: BLADE
DAMAGE (200MW)
194
196
198
200
202
204
206
208
210
212
0 10000 20000 30000 40000
VWO
80
81
82
83
84
85
86
87
0 10000 20000 30000 40000
HP Effy
5.9
6
6.1
6.2
6.3
6.4
6.5
6.6
6.7
0 10000 20000 30000 40000
HP Press Ratio
Service hours
METAL PIECE CARRIED THROUGH, BENT STATIONARY BLADES
CASE STUDY C: BLADE DEPOSITS (350MW)
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
After continuous service for periods of 6 months. Why a 10MW drop!
Correction Factors from OEM
Corrected
VWO
Output
Steam
Forced
Cool run
here
-4
-3
-2
-1
0
1
2
3
4
5
6
0 1000 2000 3000 4000 5000 6000 7000 8000
% V
ariation f
rom
new
Pressure
Ratio IP
turbine
Enthalpy
Drop
Efficiency IP
turbine
Service hours
IP Blading
DEPOSITS ON IP BLADING
CASE STUDY D: OTHER
USES OF
STAGE PRESSURES VS
FLOW/OUTPUT
Air leakage into turbine so high all air pumps had to run to start up. At 45% load, air leakage problem ceased….
Pressure at Stage 4 extraction becomes positive at that load. Leaking flange found in piping from gland to feedheater line.
If a measured stage temperature (e.g. at “A”) is higher than expected (at “B”), steam may be bypassing blades to mix with stage extraction flow: joint leak?
CASE STUDY E: USES OF
EXPANSION LINE PLOT
(500MW)
Entry to LP
casings is
below
centreline
Burnt paint seen
on LP Hood
P1 T1
P2
T 3
P3
Expansion line
Enthalpy
Entropy kJ/kg K
kJ/kg
Isentropic
enthalpy
drop
Saturated steam zone
A
T2
Temperature usually
saturation - if above,
then steam is
superheated, has
bypassed blading.
255 °C temperature
noticed at extraction to
LP2 feedwater heater
95 °C is usual temperature
(read in Control Room).
Inner
bellows
Expansion
bellows in LP
inlet pipe had
failed.
914mm
diameter,
two sets in each
of 4 pipes.
CASE STUDY F:
500MW
Initial test: Acceptance
High accuracy tests run every 2 years
Slight performance decline evident, but not unusual
After Test 4, operators noticed greater control
valves opening needed, so DCS tests run weekly
Clearly, degradation somewhere.
VWO RESULTS
Plant has DCS
Little drift proven in key instruments
Array of screen-based displays
VWO accurate tests set up, and data taken into
historian (Uniformance PHD)
VWO found both ways:
VWO Output using DCS trend close to special
tests
VWO from plant
instruments
(DCS)
VWO using special
test instruments
R
Boiler
desuperheater had
collapsed - metal
carried into turbine
ENTHALPY DROP EFFICIENCY UP TO AFTER REPAIR
(TURBINE INLET TO HP BLADING OUTLET)
81
82
83
84
85
86
87
88
89
90
31-Jan-93 15-Jun-94 28-Oct-95 11-Mar-97 24-Jul-98 06-Dec-99 19-Apr-01 01-Sep-02
HP
en
thalp
y d
rop
eff
icie
ncy %
DCS data
gave
inconsistent
point
Accurate
tests
CORRECTED PRESSURES UP TO AFTER REPAIR: AFTER
CONTROL VALVES AND FIRST STAGE
12000
12500
13000
13500
14000
14500
15000
15500
16000
16500
11-Jan-93 8-Oct-95 4-Jul-98 30-Mar-01
Date
Co
rre
cte
d p
ress
ure
s kP
a(a
bs)
Corr FSP
Corr PAGVs
ENTHALPY DROP EFFICIENCY: UP TO AFTER REPAIRS
81
82
83
84
85
86
87
88
89
90
91
31-Jan-93 15-Jun-94 28-Oct-95 11-Mar-
97
24-Jul-98 6-Dec-99 19-Apr-
01
1-Sep-02 14-Jan-04
Excessive
scatter in
DCS
results for
this
parameter
from DCS
to be
useful for
CM
INFORMATION FROM CONDITION MONITORING CAN HELP THE
MAINTENANCE DECISION – TO OPEN A TURBINE ONLY WHEN THERE IS
A TECHNICALLY AND ECONOMICALLY COMPELLING REASON.
SAME METHODS CAN BE USED TO INVESTIGATE OBSERVED
PERFORMANCE SHORTFALLS.
SPECIAL TEST INSTRUMENTATION NEEDED, BUT WORTH TRYING
USE OF DCS.
OTHER CM METHODS NEEDED: VIBRATION ANALYSIS, NDT
INSPECTION, MAYBE OIL CHECKS.
CONCLUSIONS
FURTHER DETAILS?
Ask via email: [email protected]
Papers available – Google “Ray Beebe” or email
THANK YOU – I hope it was useful to you
Postgraduate study online?
Visit www.federation.edu.au
and enter “Maintenance and Reliability Engineer”
Online Master’s degree in Maintenance and
Reliability Engineering
2000 graduates around the world over 28 years
“The need is there, the time is now!”
(Dupont 2000)