Details of a
Steam Path Audit
Paul Roediger
Encotech, Inc.
Overview of Presentation:
 Audit Overview
 Benefits
 Chronology
 Measurements
 Calculations
 Results / Report
 Conclusion
Audit Overview :
 Inspection of the steam path
(Comparison to new & clean
conditions)
 Results: clear priority for
maintenance decisions
 Benefit: maintenance dollars used
with the highest return
 Verification of maintenance
Overview:
What: Inspection of the steam path
(determined by VWO heat balance
conditions)
When: Immediately after steam path
is exposed and again after
maintenance has been
performed
Benefits
OPENING AUDIT
 Identification of degradation
 Cost-effective maintenance actions
CLOSING AUDIT
 Quality check on maintenance performed during
the outage
 Performance improvement resulting from
individual maintenance actions
 Expected return-to-service performance
Required Resources
 Computer
 Loss Calculation Software
 One or Two Auditors
 Measurement Tools
 Radial Packing Gauge
 6” Digital Caliper
 Tape measure
 Ball Gauges
 Surface Roughness Comparator
Maintenance Action Items
for B/C > 3.5
Heat Rate
Heat Rate
Benefit
Benefit
Repair cost
Action Item
(Btu/kWh)
($1,000)
($1,000) Benefit/Cost
______________________________________________________________________________
Sharpen HP stg 6 interstage packing
3.1
9.3
0.3
31.0
Sharpen HP stg 4 interstage packing
2.8
8.4
0.3
28.0
Sharpen HP stg 5 interstage packing
2.6
7.8
0.3
25.0
Sharpen HP stg 2 interstage packing
2.5
7.5
0.3
25.0
Sharpen HP stg 3-6 interstage packing
7.0
21.0
1.2
17.5
Replace IP stg 1 tip spill strip
13.0
39.0
4.0
9.8
Polish HP nozzles
13.0
39.0
4.0
9.8
Replace IP stg 2 tip spill strips
9.0
27.0
4.0
6.8
Polish IP nozzles, exhaust side
8.0
24.0
4.0
6.0
Second reheat stage minor repairs
10.0
30.0
8.0
3.8
Replace top half snout rings
23.0
69.0
19.0
3.6
______________________________________________________________________________
Maintenance Action Items
for B/C < 3.5
Sharpen stg 1 tip spill strip
0.3
0.9
0.3
3.0
Replace IP stg 3-6 tip spill strips
12.0
36.0
16.0
2.3
Sharpen stg 2 tip spill strip
0.2
0.6
0.3
2.0
Replace stg 2 interstage packing
4.0
12.0
7.5
1.6
Replace stg 6 interstage packing
3.5
10.5
7.5
1.4
Polish LP Nozzles, exhaust side
3.0
9.0
7.0
1.3
Replace stg 4 interstage packing
3.0
9.0
7.5
1.2
Replace stg 5 interstage packing
3.0
9.0
7.5
1.2
Second reheat stage major repairs
15.0
45.0
55.0
0.8
Replace bottom half snout rings
2.0
6.0
19.0
0.3
______________________________________________________________________________
Total repair cost for B/C >3.5
45.4
Total repair cost for B/C < 3.5
127.6
Chronology
 Model
 On Site
 Analysis / Report
Model
Create model using the Thermal Kit
 Design heat balance (VWO)
 Turbine cross section
 Clearance and steam seal diagram
 First stage shell pressure curve
SPA On-Site Time-Line
T UR BINE O UT AG E
Reassembly
Disassembly
S h u td ow n
Pre-Ou ta ge Te st
Op en in g S te am
Path A u dit
S ta rtu p
Upg rad e a nd
Ma in te na nc e
Clo sing Ste am
Path A u dit
Pos t-Ou tag e
Tes t
Measurements
 Geometry
 Clearances
 Surface roughness
 Damage
 Solid Particle Erosion
 Throat Openings
 Steam Path Length
Clearance Measurements
What Tooth Throttles Steam?
Slant Tooth Packing
Honeycomb Packing
Mechanical Damage
Solid Particle Erosion
Throat Opening Measurements
Ball Gauge Measurement
Surface Roughness Measurement
Miscellaneous Leakage Measurements
Cover Deposits
Nozzle Repair
On Site - Day 1
After Top is Lifted
 Inspect horizontal joint
 Measure Stationary Blade Geometry
 Measure top half tooth heights
 Measure packing clearances
 Inspect shell sealing surfaces
On Site - Day 2
Rotor Removed
 Measure solid particle erosion
damage
 Measure deposit thickness
 Measure stationary and rotating
blading surface roughness
 Inspect for mechanical damage
On Site - Day 3
 Measure bottom half tooth heights
 Measure trailing edge thickness
 Measure turbine geometry
 Inspect snout rings
Analysis / Preliminary Report
 Input data & analysis
 Print Steam Path Audit reports
 Give preliminary presentation on
site
Calculations
 Martin’s Formula
 General Flow Equation
 Dollar Value of Heat Rate
 Annual Fuel Cost Savings
 Cost of Lost Capacity
Martin’s Formula Calculation
General Flow Equation
W  KCA 
p1
 k  p2 

 2406.5 * 

v1
 k  1  p1 
W = Flow (lb/h)
K = Packing type constant
C = Rubbed coefficient
A = Area (sq in.)
P1 = Upstream Pressure (psia)
v1 = Upstream specific volume (ft 3/lb)
P2 = Downstream Pressure (psia)
k = Isentropic exponent (1.3 typical)
2406.5 = Unit conversion constant
2
k
k 1


k

 p2  
 
1  
 p1  



Common Tooth Types
ROTATING
BLADE
STATIONARY
BLADE
SINGLE – AXIAL
Flow Equation
coefficient: 0.57
SINGLE – RADIAL
Flow Equation
coefficient: 0.57
DOUBLE STRAIGHT
Flow Equation
coefficient: 0.70
coefficient:
TWO SINGLE
Flow Equation
coefficient: 0.46
DOUBLE & SINGLE
Flow Equation
coefficient: 0.52
STEP
Flow Equation
2 TEETH:
3 TEETH:
4 TEETH:
5 TEETH:
0.40
0.33
0.29
0.26
TIP SPILL STRIP CLEARANCE
Ken Cotton Chart – Reference Table [449]
GAP ave =
1
2
[(C
8
1
ave =
8 i 1
C
t ) (C L + tL)]
R+ R +
 GAPaveti
kW loss per mil excess clearance per stage:
7+ ((591.9 – 500) / (500 – 100)) x (7.0 -2.5) = 8.03 kW/mil
Dollar Value of Heat Rate Degradation
(Based on G.T.H.R.)
FC * GR * CF * 8760
HRDV 
BE *106
FC
GR
CF
8760
BE
=
=
=
=
=
Cost of fuel $/million BTU’s
Rating of turbine in KW
Turbine capacity factor in %
Hours in a Year
Boiler Efficiency
HRDV 
1
3
4
2.00 *500,000 * 75* 8760
82 *1,000,000
= $8,012.20 / year
Annual Fuel Savings - $ Year
AFS 
R
CF
F HR
SHR
R * CF * F * HR * 8760 * SHR
10,000,000,000
-
Rating of turbine in KW
Turbine capacity factor in %
Cost of fuel $/million BTU’s
Change in heat rate in %
Station heat rate BTU’s/KW HR
-
Example:
AFS 
1
3
5
500,000* 75 * 2.00 * 1.0 * 8760* 9900
10,000,000,000
= $650,430/year
Cost of Lost Capacity
K * M * R * D * 8760
L
107
Where:
L = lost revenue $/year
K = percentage of year at max. capacity (%)
M = average wholesale price of power ($/(MWh))
R = unit capacity (kW)
D = degradation in performance (%)
For:
K = 50%
M = 45 $/(MWh)
R = 600,000 kW
D = 1%
1
3
6
L = 1,182,600 $/year
Results
OPENING AUDIT
 Quantification of losses measured in pre-outage
test
 Listed cost-effective maintenance actions
CLOSING AUDIT
 Quality check on maintenance performed during
the outage
 Performance improvement resulting from
individual maintenance actions
 Expected return-to-service performance
Opening Audit Loss
Heat Rate Loss by Category
Opening Audit Loss
Heat Rate Loss by Casing
120
100
80
60
40
20
0
HP
IP
LP T
LP G
Opening Audit: Summary
Audit Category
Interstage Packings
Tip Spill Strips
Shaft End Packings
Steam Seal System Loss
Miscellaneous Leakages
Flow Path Damages
Flow Change Impact
Surface Roughness
Trailing Edge Thickness
Cover Deposits
Hand Calculations
Power Loss
kW
502.8
2333.2
1166.2
0.0
33.5
149.8
0.0
947.3
0.0
10.2
0.0
Change In
G.T.H.R.
Btu/kWh
19.91
81.87
34.44
0.00
1.76
4.36
0.00
40.28
0.00
0.53
0.00
Turbine Total
5142.9
187.71
HP Casing - Loss Summary
Audit Category
Interstage Packings
Tip Spill Strips
Shaft End Packings
Miscellaneous Leakages
Flow Path Damages
Surface Roughness
Trailing Edge Thickness
Cover Deposits
Hand Calculations
Power Loss
kW
279.7
1787.1
1096.4
0.0
27.0
414.0
0.0
0.0
0.0
Change In
G.T.H.R.
Btu/kWh
8.14
52.55
30.73
0.00
0.78
12.06
0.00
0.00
0.00
Total
3604.2
105.92
True Casing Efficiency Change
True Casing Efficiency
Apparent Casing Efficiency
6.25 %
82.84 %
82.84 %
HP Casing – Tip Spill Strips
Opening Audit
Measured Design
Clearance
in.
in.
Stage
Stage
Stage
Stage
Stage
Stage
Stage
Stage
Total
1
2
3
4
5
6
7
8
0.081
0.063
0.063
0.136
0.110
0.106
0.082
0.077
0.060
0.040
0.040
0.040
0.040
0.040
0.040
0.040
Wear
in.
0.021
0.023
0.023
0.096
0.070
0.066
0.042
0.037
Eff
Loss
%
Power
Loss
kW
Change In
G.T.H.R.
Btu/kWh
1.69
2.91
3.15
10.68
7.20
5.02
2.94
2.73
84.9
127.3
143.3
505.5
352.4
258.7
159.2
155.7
2.47
3.70
4.17
14.74
10.26
7.53
4.63
4.53
1787.1
52.55
HP Casing – Tip Spill Strips
Closing Audit
Measured Design
Clearance
in.
in.
Stage
Stage
Stage
Stage
Stage
Stage
Stage
Stage
Total
1
2
3
4
5
6
7
8
0.070
0.031
0.034
0.029
0.033
0.042
0.039
0.087
0.060
0.040
0.040
0.040
0.040
0.040
0.040
0.040
Wear
in.
Eff
Loss
%
Power
Loss
kW
0.010
-0.009
-0.006
-0.011
-0.007
0.002
-0.001
0.047
2.07
-0.97
-1.51
-1.87
-1.37
0.13
-0.06
3.90
104.5
-42.6
-68.6
-88.3
-65.7
6.8
-3.3
222.3
65.1
Change In
G.T.H.R.
Btu/kWh
3.04
-1.24
-1.99
-2.57
-1.91
0.20
-0.10
6.47
1.89
Tip Spill Strips - Opening Audit
Tip Spill Strips - Opening Audit
Tip Spill Strips - Closing Audit
Tip Spill Strips - Opening Audit
HP - Repair or Replacement Cost
Interstage
Packing
Stage
Stage
Stage
Stage
Stage
Stage
Stage
Total
1
2
3
4
5
6
7
Tip Spill
Strips
Diaphragms /
Buckets
Total
Cost
$14,230.00
$7,115.00
$7,115.00
$7,115.00
$7,115.00
$7,115.00
$3,000.00
$2,915.00
$2,915.00
$3,115.00
$2,415.00
$2,815.00
$1,715.00
$38,648.00
$23,901.00
$22,973.00
$16,110.00
$17,725.00
$14,967.00
$28,462.00
$41,648.00
$41,046.00
$33,003.00
$26,340.00
$27,255.00
$24,897.00
$37,292.00
$49,805.00
$18,890.00
$162,786.00
$231,481.00
Economic Assumptions
Assumption
Rating
320,000 kW
Capacity Factor
Cap. =1
30 %
Fuel Cost
3.5 $/ 10 6 Btu
Fuel Cost Escalation
6 %
Discount Rate
12 %
Economic Life
4 Years
Capital Escalation Rate
5 %
Year of Expenditure
1 Year
P.V. Carrying charge
1.34
(from financial Analysis/treasurer)
Exp. = 0
1
Conclusion
 Usually not everything is worth replacing
or repairing
 The Opening Audit will identify
degradation and B/C ratio
 The Closing Audit will quantify the
expected recovery
 The audit results should be reconciled
with the enthalpy drop tests.
Conclusion
 It is a fair question to ask if the
degradation would have been identified
and repaired without the use of an audit.
Some would. Some may not. And
some repairs may take place that were
not really necessary.
Questions?
1-888-Encotech
((518) 374-0924)