This paper described how costs of gas turbine ownership can be reduced based on input of condition based maintenance. Innovative thinking is required coupled with risk management.
Reducing costs with condition based maintenance, IBC conference Singapore, 2010
1. Turbo Services
Reducing Costs with Condition Based Maintenance
Dr Shaun West and Nathan Self, Sulzer Turbo Services
| slide 1
2. Sulzer Turbo Services’ experience
- over 15 years of know how developed
Turbo Services
Frame 9E/9FA 7E/7FA
Total V-series
+100 sets of parts
+75 sets of parts
+ 1500 sets of parts
+1400 sets of parts
+ 100 inspections
+25 inspections
Rotor services
(de-stacking, inspection, restacking,
balancing, NDT, life assessment)
+50
+50 projects
New and replacement parts
(consumables, combustion section,
turbine section)
+100 sets
+90 sets of parts
20units
11 units
Combustion component repairs
Blade and vane repairs
Field services
(mechanical, controls, fact finding,
minor and major inspections)
Long-term service agreements
| slide 2
3. Gas turbine segment trends
- what is ‘mature’ technology today?
Turbo Services
G and H technologies are still maturing
F-tech was first introduced 15 years ago
Improvements keep being introduced to the F-tech units
Most gas turbines can now be considered ‘mature’
Frame 5
Frame 7B
Year of
introduction
Frame 9E
Frame 7E
Frame 6B
Frame 9B
V93
and
Frame 7FA
Frame 9FA
GE
V94.3a
V94.2
Capacity
installed in
calendar year
Siemens
13E2
GT13D
13E
GT24
Alstom
GT26
WH501D
WH251B
1970
Platts, 2007
1975
1980
WH501F
WH701D
WH/MHI
WH701F
1985
1990
1995
2000
2005
2010
| slide 3
4. How can risks and costs be controlled?
- an LTSA is not for everyone
Turbo Services
Costs can be ‘high’
LTSAs with the manufacturer
Management of technology risk for
introductory technologies
Can be ridged in structure
Extra works normally at ‘list price’
Service delivery is more flexible
Suitable for mature technologies
LTSAs with a non-OEM
Good tool to limit price risks
Extra works normally at agreed rates
Life management possibilities
Management and logistics can be an issue
Transactional services
Costs can be lower – all technical risk
remaines with the buyer
Life management possibilities
| slide 4
5. Sweating the asset
- where can the most value be created?
Turbo Services
Where can additional value safely be
extracted?
Parts costs
Repair costs
Cost saving creates value
Field service TA costs
Field service craft labour
Parts’ life extension
Extension of inspection intervals
Engineering judgment adds value
Upgrading of capability
| slide 5
6. Driving cost savings to create value
Turbo Services
Good procurement driving costs out
Cost saving of 10% on repairs
Cost saving of 10% on CI field services
CI/CI/HGP/CI/CI/MI cycle
What is the cost saving?
Six day outage
Repair costs
Cost per CI
100,000USD
200,000USD
2 MI cycle (12 years)
40,000
80,000
120,000
The unit is not put at risk directly…
… risk of poor outage performance
… risk of poor repair life
| slide 6
7. Value creation from engineering judgment
Turbo Services
Using engineering know how to create value
Removal of combustion inspection
CI/CI/HGP/CI/CI/MI cycle
What is the value created?
Six day outage
Repair costs
Generation gains
Cost per CI
2 MI cycle (12 years)
100,000USD
800,000
200,000USD
1,600,000
100MWx24hx6dx25USD/MWh
360,000USD
2,880,000
5,280,000
This example is based on no additional repair costs!
A little unrealistic as repairs on the combustion capitals may be more extensive
The key is how to do this without putting the unit at risk…
| slide 7
9. Corrosion and oxidation
- three different damage mechanisms
Cr2O3
Turbo Services
TBC
Al2O3
Protective layer
Inter-diffusion
Thermo mechanical fatigue
Attack
Type II
Hot Corrosion
500
600
Type I
Type I
Hot Corrosion
700
800
Temperature (°C)
900
Oxidation
1000
1100
| slide 9
10. Material degradation
- material strength reduces over time
Gamma prime strengthens super
alloys
Turbo Services
Heat treatments can restore the
structure
Time at high temperature causes
rounding of the crystals
LE
CC
CV
TE
TIP
MIDDLE
ROOT
γ’ precipitate size changes with time & temperature
| slide 10
11. Creep
- Creep damage cannot be recovered
Turbo Services
Material properties are important, like
grain size and volume of γ’precipitates
Strain [-]
Slow deformation at constant stress
level at high temperatures ( T >
0.4Tm )
Creep is a thermally activated process
Strain rate increase with stress and
temperature
Life time reduces with increase in
stress and temperature
| slide 11
12. Fretting
- damage minimization is key
Turbo Services
What: material removal as a result of
sliding wear
Contact between two surfaces
Vibration
Where: transition pieces
Seals
Mounting brackets
Fix: wear resistant coatings or linings are
usually efficient (W-Cr carbides, Stellites)
| slide 12
13. 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
Δσ [MPa]
LCF
Fatigue limit
HCF
100
1000
10000
100000
1000000 10000000
Number of cycles [#]
| slide 13
19. Blade re-design to meet a customer’s needs
A customer found that their blades were
failing early in life due to a deformation on the
shroud of the turbine blades
Turbo Services
Original with shroud
Working with the customer and their
insurance company, a tailor-made solution
was developed
The new design has proven itself in operation
The new design provides lower operational
risk because the deformation no longer
plagues the machine
Modified without shroud
Major cost saving:
24kEOH parts now lasting 24k+24kEOH
| 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
Major cost saving:
A new rotor can cost 5M USD
An unplanned failure will cost the owner and insurer +10M USD each
Example of FEA on rotor disk
| slide 20
21. Damaged turbine stub shaft
- repaired and fit for service
Turbo Services
Emergency shut down damaged turbine
stub shaft
Stub shaft was machined, welded and then
machined to original dimensions
Rotor rebuilt and put back into operation
Speed was key for the owner
Major cost saving:
Rotor returned to service within 30 days
| slide 21
22. Extending outages
- removing an unplanned 8000EOH inspection
Turbo Services
Review of the weak parts of the turbine
Upgrades on the weakest areas
Flow down of advanced technologies
Transfer of technologies used on other units
Understanding of the full hot gas path
FE analysis
Temperature mapping
CFD
Modes of degradation
Own (S West) experience
Burner segment plates – early failure
Weaknesses from fretting and overheating
Solution – low risk, based on coatings
| slide 22
23. Frame 9FA compressor
- strip, replace, rebuild of the compressor
Turbo Services
Reverse engineering
Determination of natural frequencies
3D scanning
Physical component
Finite element measurement
Computational fluid dynamics
3D solid model
Over 20 F-tech rotors
| slide 23
24. Making run/no-run decisions
- I am stuck in the middle…
Turbo Services
Engineering judgment helps you to make better decisions
Helps to create value and save cost
‘We need to have a decision
- NOW!’
‘What’s the risk of running
on?’
‘There are high prices
available - we’re losing
opportunity’
‘I don’t want to know the
technical details..’
‘How long can we
run safely for?’
‘How long will it take to fix
and how much will it cost’
| slide 24