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Maintenance of V94 series of gas turbines, Power Gen Russia, Moscow, 2010
1. Russia Power 2010
Turbo Services
Maintenance of V94.0/V94.2 series of gas turbines
Dr Shaun West and Sjef Mattheij MSc, Sulzer Turbo Services
| slide 1
2. Contents
Turbo Services
Background
Component life analysis
Corrosion and oxidation
Material degradation
Creep
Fretting
Fatigue
Rotor life management
The manufacture of gas turbine blades
Summary
| slide 2
3. Sulzer Turbo Services’ experience
- over 15 years of know how developed
Turbo Services
V94.2 series
Total V-series
Combustion component repairs (burners,
star plates, mixing chambers, hot gas
casings)
50 sets of parts
76 sets of parts
Blade and vane repairs
672 sets of parts
1485 sets of parts
16 inspections
28 inspections
35 projects
56 projects
37 sets of parts
93 sets of parts
10 units
11 units
Field services
(mechanical, controls, fact finding, minor and
major inspections)
Rotor services
(de-stacking, inspection, restacking,
balancing, NDT, life assessment)
New and replacement parts (consumables,
combustion section, turbine section)
Long-term service agreements
| slide 3
4. 15 years of component repair experience
- development of proprietary know how
Turbo Services
Repair experience starting in the 1990s
Compressor section
Burners
Flame tubes
Hot gas casings
Power turbine
Build up of proprietary know how
Based on earlier and later V-series units
Based on repairs of gas turbines of other
OEMs
Based on operator feedback
| slide 4
5. Repair of blades
- metallurgical understanding key to repairs
Known operational issues
Turbo Services
Repair processes
IN 738/Sicoat 2231
Striping of coating
Cracking leading edges (row 1)
Heat treatment
IGA
NDT
Welding
Overlay repair by slurry-brazing
Blending
Heat treatment
Coating (where applicable)
Sulzer inspection techniques
X-ray
Boroscope inspections
Thermographic analyses
| slide 5
6. Repair of vanes
- metallurgical understanding key to repairs
Known operational issues
Turbo Services
Repair processes
Nitration of IN 939
Striping of coating
Fatigue cracking
Heat treatment
Distortion
NDT
Welding
Overlay repair by slurry-brazing
Blending
Heat treatment
Coating (where applicable)
Sulzer inspection techniques
X-ray inspection
Visual inspection of internals
Dimensional inspection: tooling
| slide 6
7. Repair of combustion parts
- metallurgical understanding key to repairs
Known operational issues
Turbo Services
Repair processes
Nitration of IN617
Assessment of damage
Fatigue cracking
Restoration of shape
Distortion/overheating
Solution heat treatment
Removal of damaged areas
Sulzer inspection techniques
Visual inspection
Repair and replacement of damaged parts
Dimensional inspection: tooling
Stress relieve heat treatment
Metallurgical inspections
Thermal Barrier Coating application
Hard facing and assembly of auxiliaries
| slide 7
8. 2001 the first major overhaul
- planning and know how key to success
Turbo Services
Scope
Site works (fact finders, QA, site management, technical advisors…)
Rotor removal, de-stack, re-stack and balancing
All blades and vanes repaired
Replacement of consumables
Challenges
Unit has been build within existing power plant
Unit was an early .0 version
| slide 8
9. Inspection challenges
- rotor line out is a critical issue
Turbo Services
Correct procedures are required
Attention to x, y and z direction (more
than with annular combustors
Correct tolerances on repair mixing
chambers and HGC
Know how is key to success
| slide 9
10. 10 years experience with replacement parts
- new parts based on repair experiences
Turbo Services
Special tooling critical for the component
repair
Experience based on repair and manufacture
of many different silo combustion systems
Weld procedures important to maintain
dimensional integrity
| slide 10
11. Contents
Turbo Services
Background
Component life analysis
Corrosion and oxidation
Material degradation
Creep
Fretting
Fatigue
Rotor life management
The manufacture of gas turbine blades
Summary
| slide 11
12. Corrosion and oxidation
- three different damage mechanisms
Cr 2 O 3
Protective layer
Turbo Services
TBC
Al 2 O 3
Inter-diffusion
Thermo mechanical fatigue
Attack
Type II
Hot Corrosion
500
600
Type II
Type
Hot Corrosion
700
800
Temperature (°C)
900
Oxidation
1000
1100
| slide 12
13. Material degradation
- material strength reduces over time
Material Degradation
Gamma prime strengthens super
Dissolution and growth of γ’- precipitates
alloys
Turbo Services
Heat treatments can restore the
Sulzer Turbo Services
structure
Time at high temperature causes
Gamma Prime Size / Temperature distribution
rounding of the crystals
LE
CC
CV
TE
TIP
MIDDLE
ROOT
γ’ precipitate size changes with time & temperature
| slide 11
| slide 13
14. Creep
- Creep damage cannot be recovered
Turbo Services
Slow deformation at constant stress
level at high temperatures ( T >
0.4Tm )
Material properties are important, like
grain size and volume of γ’precipitates
Creep is a thermally activated
Strain rate increase with stress and
temperature
Life time reduces with increase in
stress and temperature
| slide 14
15. Fretting
- damage minimization is key
Turbo Services
Material removal as a result of sliding wear
Contact between to surfaces
Vibration
Transition pieces
Seals
Mounting brackets
Wear resistant coatings or linings are
usually efficient (W-Cr carbides, Stellites)
| slide 15
16. Cyclic fatigue
- regular visual inspections are important
High cycle fatigue
Turbo Services
Low cycle fatigue
Large number of cycles until failure (>100,000
cycles)
Low number of cycles until failure
(<100,000 cycles)
Crack initiation can take a long time
Crack initiation period relatively short
Required stress amplitude is relatively low
Stress amplitude is high
Vibration can be caused by:
Tip rubbing
Resonance
Aerodynamic instabilities
∆σ [MPa]
LCF
Fatigue limit
HCF
100
1000
10000
100000
1000000 10000000
Number of cycles [#]
| slide 16
18. Low cycle fatigue
- start/stop related
Turbo Services
IN939 vanes suffering LCF following imbrittlement of the base material
| slide 18
19. Contents
Turbo Services
Background
Component life analysis
Corrosion and oxidation
Material degradation
Creep
Fretting
Fatigue
Rotor life management
The manufacture of gas turbine blades
Summary
| slide 19
20. Rotor life management
- extending operation safely
Turbo Services
Rotor material can become brittle
Replica and phased array NDT are two
assessment tools
Rotor operational history important
Rotors can suffer low cycle fatigue
Finite element modeling provides stress data
Some damage can be repaired/replaced
Example of FEA on rotor disk
| slide 20
21. Contents
Turbo Services
Background
Component life analysis
Corrosion and oxidation
Material degradation
Creep
Fretting
Fatigue
Rotor life management
The manufacture of gas turbine blades
Summary
| slide 21
22. The manufacture of gas turbine blades
- over 35 years of experience
Turbo Services
Reverse engineering started in 1980s
Supporting Russian gas pumping units
Many different designs for different units
Key processes
Measurements
(parts and fit with adjacent parts)
Understanding the design intent
3D-CAD drawings
Casting
Machining
| slide 22
23. Contents
Turbo Services
Background
Component life analysis
Corrosion and oxidation
Material degradation
Creep
Fretting
Fatigue
Rotor life management
The manufacture of gas turbine blades
Summary
| slide 23
24. Summary
- driving towards improved performance
Turbo Services
Condition based maintenance supported by Sulzer can:
Extend operational life
Have a positive impact on total maintenance costs
Helps to allow informed decisions concerning ‘repair’ or ‘replace’
Provide the necessary information on critical components to manage component
life, turbine life and inspection intervals.
C&I sites services
Trouble shooting / hot line / remote condition monitoring
Compressor
Mechanical site services
Planned and
unplanned
maintenance
Parts
Blades and vanes
Combustion system
Repairs
LTSAs
Rotor
Component
| slide 24