Steam Path Audit of Steam Turbine

Steam Path Audit

encotech, Inc. encotech Inc.

Overview 

What is a Steam Path Audit (SPA)?



Objective & Benefits



Chronology of a Steam Path Audit



Damage



A Case study

Overview 

What is a Steam Path Audit (SPA)?



Objective & Benefits






Damage



A Case study

What is a Steam Path Audit? 

A detailed inspection of the stationary and rotating steam path components



An accounting of performance losses on a stageby-stage basis



An accounting of performance losses on a component-by-component basis



A presentation of losses in power and heat rate

Impulse Blading

DIAPHRAGM TIP SPILL STRIPS

TENON

TIP LEAKAGE COVER OR SHROUD SHELL

STEAM FLOW

ROTATING

STATIONARY

BLADE

BLADE

PRESSURE

BOWL PRESSURE

ROOT LEAKAGE

ROOT SPILL STRIPS DOVETAIL

BALANCE HOLE FLOW BALANCE HOLE

PACKING WHEEL

INTERSTAGE PACKING LEAKAGE

SHAFT

The specific areas of concern addressed by the audit are: 1) Leakages: - past stationary stage blading - past rotating stage blading - past shaft end packings where rotors emerge from casings - across poorly fitting joints - other miscellaneous leakages 2) Surface finish degradation: - deposits - corrosion - solid particle erosion - mechanical damage

3) Flow blockages from: - deposits - foreign objects - mechanical damage

4)

Flow path modification from: - solid particle erosion - water droplet erosion - mechanical damage

Objective of a SPA



The objective of the audit is to assess the condition of the turbine steam path to identify degradation in thermal performance of the unit and to point out the cause and location of power and efficiency losses.

Benefits of a SPA 

Provides detailed inspection of steam path



Quantify heat rate, power and efficiency impact on component-by-component basis



Aid economic decisions during the repair outage



Prioritize maintenance decisions on a benefit-to-cost ratio



Quantify the quality of turbine repairs by performing a closing steam path audit



Provides excellent record/history of equipment condition for future reference

The Outage Time-Line TURBINE OUTAGE

Shutdown

Startup

Disassembly

Pre-Outage Test

Opening Steam Path Audit

Reassembly

Upgrade and Maintenance

Closing Steam Path Audit

Post-Outage Test

Results 







Quantification of losses measured in pre-outage test Quality check on maintenance performed during the outage Performance improvement resulting from individual maintenance actions Expected return-to-service performance


Computer Model 

Create turbine model at STEAG’s office using the Thermal Kit 

Design heat balance (VWO)



Turbine cross section



Clearance and steam seal system diagram



First stage shell pressure curve

Coordinate Activities 

Coordinate activities with owner  





Plan around grit blasting schedule Place upper half of casing w/ horizontal joint up or lay on ground w/ trailing edges up Leave all packing (interstage & shaft end) in place until measured. This speeds SPA process significantly All stages must be inspected prior to grit blasting

Sequence of Events 

Inspect casing horizontal joint for leakage paths



Measure blade geometry



Measure packing teeth, interstage, tip, root, and & shaft end



Create a photographic record of the steam path



Geometric data for the steam path must be obtained to properly model turbine

Solid Particle Erosion

Mechanical Damage

Cover Deposits

Blade Deposits

Foreign Object Damage

Flow Path Damage

Surface Roughness

encotec h, Inc. encotech

Surface Roughness

Root Cracks

Tip Spill Strip

Clearance Measurements

Surface Roughness

Geometry Measurements

INDIAN EXPERIENCE A Case Study

TYPICAL 200 MW 

Commissioned in the year 1984



Tandem compound two flow LP steam turbine



HP/IP – an opposed flow design



Output – 206,260 kW at VWO condition



Initial steam conditions



Pressure 14710 kPa, Temp. 535/535 deg C



Exhaust Pressure 10.49 kPa



Shaft speed 3000 rpm



Total thirty three stages, Six Extractions

Preliminary Observations 





HP Casing  Severe Flow Path Damage on stages 2, 3, and 4  Tip, Root, and Interstage Packings rubbed IP Casing  Severe Flow Path Damage on stages 11, and 12  Tip, Root, and Interstage Packings rubbed LP Casing  Tip, and Interstage Packings rubbed  Slant End Packings severely rubbed

Change in Power by Category – Total All Casings OPENING

CLOSING

AUDIT

AUDIT

7000

6738.2

7000

6000

6000

5000 ) W k ( 4000 s s o L r 3000 e w o P 2000

) W5000 k ( s s 4000 o L r e 3000 w o P2000

4795.3 4177.8 3477.5 2740.4

2506.6

1447.4

1000

4570

3241.1

1975.3

1000 0

e s g g a i n t s r k c e t a n P I

l l i s p p S i r p t i S T

s g n i k c a P d n E

s u s o e e g n a a k l l e a e c L s i M

h t e a g P a w m a o D l F

e g t n c a h a C p m w I o l F

s e s c e a n f r h u g S u o R

s r t e i v s o o C p e D

s n o d i n t a a l H u c l a c

e g s d s E e n g k n i c i l h i a T r T

e s g g a i n t s r k e c a t n P I

2077.8

282.4

260.2

0

s p i r t S l l i p S p i T


s s s e h e e s t u s r t r n g s y g i o s a g n t e e o d s e e s i c a d e e P a c a n v o n t E e v n g h a n o h a f l r g o p a a w m k c e a u g l n o a C p u u C D l k l c e H i c l m S o l e a F D w I i i h R c e a a o R l s L c r T i T F M

Power Loss by Casing OPENING

CLOSING

AUDIT

AUDIT 12000

12000 10499.3

10000

10000

) W k ( s s o L r e w o P

) 8000 W k ( s s o L 6000 r e w o P 4000

8000

6000

4000

1928.6

2000

1123.6

1415.8

6738.2

6495.5

2000

1023.9

843.4

IP

LP Gov

802.9

0

0 HP

IP

LP Gov

LP Gen

HP

LP Gen

Recovery

Change in Power by Category – HP Casing OPENING

CLOSING

AUDIT

AUDIT

5000

5000 4270.6

4000

) W k ( s 3000 s o L r e 2000 w o P 1000

) W k ( s 3000 s o L r e 2000 w o P

2627.5

1630.7 1300.6

e s g g a n t i s r k c e t a n P I

1037.0

1083.8

h t e a g P a w m o a l F D

s e s c e n a h f r g u S u o R

1000

669.8

120.5

0

4003.7

3992.1

4000

l l i s p p S i r p t i S T


s u o s e e n g a a l l k e a c e s L i M

h t e e a g g t P a n a c h a w m p a C o l m F D w I o l F


s r t i e s v o o p C e D

s n o i d t n l a a H u c l a c

e g d s s E e n g k n c i i l i h a r T T

0

e s g g a n t s i k r e c t a n P I

262.1



y r e v o c e R

Change in Power by Category – IP Casing OPENING

CLOSING

AUDIT

AUDIT

2000

2000

1500

1500 1206

) 1000 W k ( s s o L 500 r e w o P 0

-500

-1000

965.3

355.4

-639.9

e s g g a n t i s r k e c t a n P I

l l i p s p S i r t p i S T

41.8



h s t e e a g g e s n t P a a c c e n a h h a f w m a C p r o u g l D m S u F w I o o R l F

s r t i e s v o o p C e D


e g s d s E e n g k n c i l i i h a r T T

) 1000 W k ( s s o L 500 r e w o P 0

-500

-1000

938.3

904.7 591.2

17.0

e s g g a i n t s r k e c a t n P -527.3 I

4.6


h e t a g P a w m o a l F D

s s e e c n a h f r g u u S o R

s n o i d t n l a a u H l c a c

y r e v o c e R

Change in Power by Category – LP Gov Casing OPENING

CLOSING

AUDIT

AUDIT

1000

1000

800

800 ) W k ( s 600 s o L r e 400 w o P

) W k ( s 600 s o L r e 400 w o P

473.7 413.1

226.40

530.1

280.2

249.4

200

200

55.3 10.4

0

e s g g a n t i s r k c e t a n P I

l l s i g p s p n S i i r k p t i S c T a P d n E

8.7


h s s t e e s r t i a g g e e e n s P a a t c c n v o a h a f h o p w m C e o a C p r u g l u D D m S F w I o o R l F

s n o d i t n l a a H u c l a c

e g s d s E e n g k n c i l i i h a r T T

0

e s g g a i n t s r k e c a t n P I


h t e a g P a w m o a l D F

s s e e c n a h f r g u u S o R


y r e v o c e R

Change in Power by Category – LP Gen Casing OPENING

CLOSING

AUDIT 800

) W k ( s 600 s o L r e 400 w o P

AUDIT

1000

1000

800

751.5

407.9

195.8

) W k ( s 600 s o L r e 400 w o P

612.9 575.2

200

200

153.4 67.4

60.60

7.0

0

l e s l s i g g p s g p a n n S i t i r i s t k k p r c i e a T S c a t P n P I d n E

0

s h s e s s t e e u t n g s g r i e s o s a g e o d s e n s t i c a P e e a c a n v o d t E e n g w m h a f n o p a g n a a o a C p r h g C e a l l u i n k u l k l H c u D c m S o l e a F D w I l i i h c e a o a R l s L c r T i F T M

e s g g a n t i s r k e c t a n P I


h e t a g P a w m o a l F D


s n o d i t n l a a u H c l a c

y r e v o c e R

Change in Heat rate by Category – Total All Casings OPENING

CLOSING

AUDIT

AUDIT 424.11

400

400

) h W k 300 / J k ( s s o L 200 R . H . T . G 100

116.55

110.56 63.03

45.72

) h W k 300 / J k ( s s o L 200 R . H . T . G 100

245.53 178.58 112.37

55.28

8.17

0

s g n i k c a P e g a t s r e t n I



s e g a k a e L s u o e n a l l e c s i M

e g a m a D h t a P w o l F

t c a p m I e g n a h C w o l F

63.63

43.45

32.97

s s e n h g u o R e c a f r u S

s t i s o p e D r e v o C

s n o i t a l u c l a c d n a H

s s e n k c i h T e g d E g n i l i a r T

s s o l l a t o T

y r e v o c e R

0

s g n i k c a P e g a t s r e t n I

11.22

6.69



s e g a k a e L s u o e n a l l e c s i M

e g a m a D h t a P w o l F

t c a p m I e g n a h C w o l F

s s e n h g u o R e c a f r u S

s t i s o p e D r e v o C

s n o i t a l u c l a c d n a H

s s e n k c i h T e g d E g n i l i a r T

s s o l l a t o T

y r e v o c e R

Heat rate loss by Casing

OPENING

CLOSING

AUDIT

AUDIT 424.1

400

400

) h 300 W k / J k ( s s o L 200 R . H . T . G

) 300 h W k / J k ( s s o L R . 200 H . T . G

241.5

245.5

178.6 146.3

100

100 55.4

44.8

56.5 24.0

33.6

31.9

0

0 HP

IP

LP Gov

LP Gen

Total loss

Recovery

HP

IP

LP Gov

LP Gen

Total loss

Recovery

Steam Path Audit of Steam Turbine

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