Transcript RLA Study of U # 3 Boiler (200 MW)

Condition Assessment of
Supercritical Boilers-Challenges Ahead
Dr. S.K.Nath
Engineering Officer
Central Power Research Institute
Thermal Research Centre
Koradi
Nagpur-441111
Supercritical Technology in India
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Availability of coal both in quality and quantity
Reduction in emission-environmental obligation
Low Average efficiency of power plants in India in the range
of 27% - 34%.
Achieving the required economic growth
Major Power Producer NTPC Ltd. has gone for first
Supercritical Units in India followed by others.
Estimated 25 Nos. of SC projects are under different phase of
development while more than 35 projects are under proposal
stage.
Rankine Cycle
Supercritical Rankine Cycle
3740 C;
225 Kg/cm2
Enhanced steam parameters
require superior materials
Requirements of materials for
high-temperature application
Adequate strength to resist deformation-high temp.
and pr.
2. Adequate fatigue strength against vibratory stress
3. Sufficient ductility to accommodate cumulative
plastic strain and notch strength against stress
concentrations
4. Good resistance to service environment to
withstand oxidation, corrosion and erosion
5. Structural ability to resist damaging metallurgical
changes at operating conditions
1.
Requirements of materials for hightemperature application (contd.)
6. Ease in fabrication (machining, forging, casting and
welding)
7. Low coefficient of thermal expansion to resist thermal
stresses
8. Good thermal conductivity to minimise thermal gradient
9. Low density to provide high strength-to-weight ratio – for
last staging blading of large steam turbine
10. Availability of long-term test data to validate the design
11. Availability in the desired size and shape
Comparison of allowable stresses between
conventional and advanced materials
Supercritical Boiler
Item
Section
Material Specification
(ASME)
Water Wall
Tubing
SA213-T22
SA335 - P12
Header & Piping
SA335 - P91
SA213-T12
Superheater
SA213-T23
Tubing
SA213-T91
SUPER 304H
SA106-C
Header & Piping
SA335 - P12
SA335 - P91
SA210Gr.C
Reheater
SA213-T12
Tubing
SA213-T23
SA213-T91
SUPER 304H
Header & Piping
SA106-C
Tubing
SA210-C
Economiser
Seperator Storage Tank
SA302-C
Various damage mechanisms in
supercritical boilers
• Short term damage mechanisms:
Erosion, Fireside corrosion, shortterm overheating
• Long term damage mechanism:
Creep, Thermal Fatigue
Operational effects on
supercritical boiler components
• High temperature effect (ageing)
• High temperature corrosion (ash
attack)
• High velocity flue gas with particulate
burden (erosion)
• Thermal cycling
• Steam side oxide scale growth
• Maintenance repair (weld, foreign
material entrapment)
Manifestation
• Mechanical
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Material loss
Wall thinning
Weld defect
Crack
Swelling
Slagging, fouling
Loss of material strength
Manifestation (contd.)
• Metallurgical
 Creep life
 Structural integrity
• Steam Starvation
 Sudden Rupture
Various damage mechanisms and
suitable NDE methods
Damage Mechanism
NDE Methods for detection
Erosion
Visual Examination (VE), Ultrasonic Thickness Survey
Blockade in water circuit
Fibroscopy
Welding defects
Ultrasonic Test (UT), Magnetic Particle Test (MPT), Dye
Penetrant Test (DPT), Radiographic Test (RT)
Creep
In-situ Metallography, Hardness Measurement
Oxide Scale growth
Ultrasonic Test (UT)
Thermal fatigue crack detection
and sizing
Ultrasonic Time of Flight Diffraction (TOFD) inspection,
potential drop technique
Short Term overheating
In-situ Metallography, Hardness Measurement
Swelling
Dimensional Measurement (OD)
What is Creep?
-The time dependent, thermally assisted
deformation of components under load
(stress) is known as creep.
Structural
Microstructure Action needed
Classificati features
on
Expended
life
fraction
Undamaged Ferrite &
pearlite
None
0.12
A
Isolated
cavities
None until next major
scheduled maintenance
outage
0.46
B
Oriented
cavities
Replica test at specified
0.50
interval preferably within 1.5
to 3 years
C
Linked cavities Limited service until repair
0.84
(micro cracks) and better to inspect within 6
months
D
Macro cracks
Immediate repair
1.00
In-situ metallography (Replication)
Major Findings
Bulging
Damaged microstructure (creep cavities)
Fatigue
Start-ups, load changes
Crack initiation – Stress Analysis, Nf
Crack propagation
CRACK PROPAGATION
Initial
Crack length – Assessed by a
suitable NDE technique (e.g. Ultrasonic)
Critical
Crack length – Assessed based
on the prevailing stress field and
geometry of the job.
Crack propagation
Paris Law:-
da/dN = ckn
c, n = material
constants
For k = M(a)
aiac a-n/2da = cnMn/2dN;
M = parameter related flaw shape
Ultrasonic Time of Flight
Diffraction (TOFD) Inspection
TOFD - How it works
COMPLEX WELD WITH DISSIMILAR THICKNESS
Specimen simulating complex geometry weld namely terminal
weld between pipe and valve containing various defects
t LW 
t BW 
t1 
t2 
S2 T 2 
S  x 2aZ
C
T  H 2  x 2  a  B2
C
S2  d2 
S 2  d  h 2 
d  H 2  x 2  a  B 2
C
d  h  H 2  x 2  a  B 2
C
Indian Boiler Regulation
(IBR)
Statutory Perspective
Objectives:
1. Safe Operation
2. Update Boiler memo
Statutory Perspective (Contd.)
 Boiler Act
 IBR- Rules & Regulations
 Prescriptions
• Authority
– Inspectorate of Boilers
• Jurisdiction – Within the State Territory
• Boilers
> = 22.75 Litres
> = 1,00,000 Hours
> = 25 years old
Statutory Perspective (Contd.)
•
Agency: Approved as per Act
•
Methodology:
•
Table 1 and Table 2
•
NDT inspection of Drum, Headers, Pipes
&Tubes by Visual, UT,DPT, Replication, OD
& Thickness, Fiber optic inspection,
Hardness, Oxide scale thickness measurement.
TABLE -1
Component
Visua
l
Ultrasonic
testing
Magnetic
Particle
Inspection
Liquid/
Dye
Penetrant
Inspection
Replication
Sampling
Deposit
Analysis
Outside
Diameter
And
Thickness
Fibroscopic
Inspection
Hardness
Other
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
Drum(Steam)
Yes
Yes
No
Yes
Yes
No
Yes
Yes
No
Yes
Water Drum
Yes
Yes
No
Yes
Yes
No
Yes
Yes
No
Yes
Low Temp.
Headers
Yes
No
No
Yes
No
No
No
Yes
Yes
Yes
Attemperator
Header
Yes
Yes
No
Yes
Yes
No
No
Yes
Yes
Yes
High Temp.
Economiser
tubes
Yes
No
No
No
No
Yes
No
Yes
No
No
Low Temp.
Economiser
tubes
Yes
No
No
No
No
Yes
No
Yes
No
No
Convection
Superheater
coils
Yes
No
No
No
No
Yes
Yes
Yes
No
Yes
Primary
Super heater
coils
Yes
No
No
No
No
Yes
No
Yes
No
Yes
Pre final
Super heater
coils
Yes
No
No
No
No
Yes
No
Yes
No
Yes
Swell
measur
ement
TABLE -1 (Contd.)
Component
Visua
l
Ultrasonic
testing
Magnetic
Particle
Inspection
Liquid/
Dye
Penetrant
Inspection
Replication
Samplin
g
Deposit
Analysis
Outside
Diameter
And
Thickness
Fibroscopic
Inspection
Hardness
Others
Final
Super heater
coils
Yes
No
No
No
No
Yes
No
Yes
No
Yes
Reheater coils
Yes
No
No
No
No
Yes
No
Yes
No
Yes
High Temp.
headers
Yes
Yes
No
Yes
Yes
No
No
Yes
Yes
Yes
Final
Super heater
header
Yes
Yes
No
Yes
Yes
No
No
Yes
Yes
Yes
Swell
measur
ement
Reheater
header
Yes
Yes
No
Yes
Yes
No
No
Yes
Yes
Yes
Swell
measur
ement
Main steam
Piping
Yes
No
No
No
Yes
No
No
Yes
No
Yes
Platen super
Heater header
Yes
Yes
No
Yes
Yes
No
No
Yes
Yes
Yes
Primary super
heater header
Yes
Yes
No
Yes
Yes
No
No
Yes
Yes
Yes
TABLE -1 (Contd.)
Component
Visual
Ultrasonic
testing
Magnetic
Particle
Inspection
Liquid/
Dye
Penetrant
Inspection
Replication
Sampl
ing
Depo
sit
Anal
ysis
Outside
Diamet
er
And
Thickn
ess
Fibrosc
opic
Inspecti
on
Hardness
Economiser
Header
Yes
No
No
Yes
No
No
No
Yes
No
No
Auxiliaries
Yes
No
No
No
No
No
No
Yes
No
No
Boiler Bank
Tube
Yes
No
No
No
No
No
No
Yes
No
No
Water Wall
Yes
No
No
No
No
Yes
No
Yes
No
No
Furnace Water
Wall
Yes
No
No
No
No
Yes
No
Yes
No
No
others
Table – 2.
Component
Visual
Ultrasonic
testing
Magnetic
Particle
Inspection
Liquid/
Dye
Penetrant
Inspection
Replicatio
n
Samplin
g
Deposit
Analysis
Outside
Diameter
And
Thickness
Fibroscopic
Inspection
Hardness
Drum(Steam)
Yes
No
No
Yes
No
No
No
Yes
No
No
Water Drum
Yes
No
No
Yes
No
No
No
Yes
No
No
Economiser
Tubes
Yes
No
No
No
No
Yes
No
Yes
No
No
Convection
Super Heater
coils
Yes
No
No
No
No
Yes
No
Yes
No
No
Primary Super
Heater coils
Yes
No
No
No
No
Yes
No
Yes
No
No
Final Super
Heater coils
Yes
No
No
No
No
Yes
No
Yes
No
No
High Temp.
Headers
Yes
No
No
Yes
Yes
No
No
Yes
Yes
No
Other
Non
destru
ctive
oxide
thickn
ess
inspe
ction
TABLE -2 ( Contd.)
Final Super
Heater Header
Yes
No
No
Yes
Yes
No
No
Yes
Yes
No
Economiser
Header
Yes
No
No
No
No
No
No
Yes
No
No
Auxiliaries
Yes
No
No
No
No
No
No
No
Yes
No
Boiler Bank
Tube
Yes
No
No
No
No
No
No
Yes
No
No
Water Wall
Yes
No
No
No
No
Yes
No
Yes
No
No
Main steam
Piping
Yes
No
No
No
No
Yes
No
Yes
No
No
Swell
meas
ureme
nt
Statutory Perspective (Contd.)
OUTCOME
• Scientifically assured safe operation
for a specified period.
Role of Indian Boiler Regulation
(IBR)
With age of currently available supercritical
boilers in their infancy, the deployment of
NDE will be limited to failure analysis and
condition assessment of the component for
quality control of repair programmes during
any forced outage event and IBR relevance
may be seen here.
Issues of Supercritical Technology in India

Critical issues to be resolved for faster
development :
Technological issues :a) Water wall cracking
b) Negative flow characteristic
c) Slagging.
d) Designing as per Indian condition
e) Welding technology for new material
Issues of Supercritical Technology in India
(contd.)
Operation & Maintenance Issues:
Availability of sufficient field data w.r.t. material
behavior, boiler tube leakage (BTL)
 Availability of critical spares for supercritical
plants.
 Availability of skilled manpower
 Large number of foreign suppliers of SC Power
Plants , but have comparatively long delivery
period .
 Availability of contractors for O&M activities
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Reference:
1. R.Viswanathan, “Damage Mechanisms and Life Assessment of High Temperature
Components”, ASM International, Metals Park, Chio 44073.
2. Arindam Sinha and Akhilesh Kumar Singh (2011), New Era in Indian Thermal Power
Sector-Evolvement of Supercritical Technology, Workshop on Remnant Life Assessment
(RLA) Study of Boilers organized by Central Power Research Institute on 4-5th March, 2011
at Raipur (CG)
3. Modern Power station practice, Boilers and Ancillary plant, BEI Volume – B.
4. Indian Boiler Regulation, Act 1923 & Regulations 1950, Akalank Publications, Delhi-110
006, 9th ed., July 2007.
5. S.K.Nath et al (2011), Non-Destructive Evaluation in Remnant Life Assessment (RLA)
study of Boilers Workshop on Remnant Life Assessment (RLA) Study of Boilers organized
by Central Power Research Institute on 4-5th March, 2011 at Raipur (CG)
6. B.J.Robbins, D.M.Farrell, J. Stallings and S. Cardoso, The Monitoring of Circumferential
Fatigue Cracking of Furnace Tubes in Supercritical Boilers, Rowan Technologies Ltd.,
Manchester, UK and Electric Power Research Institute, Palo Alto, CA, USA.
7. Kulvir Singh (2006), Advances in Materials for Advanced Steam Cycle Power Plants,
BHEL Journal