gas turbine maintenence aspects
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Heavy-Duty Gas TurbineOperatingand MaintenanceConsiderations
YDERABAD
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2HDGT.PPT/
HYDERABAD GT INSPECTIONS
Running Inspections
Standby Inspections
Shutdown Inspections
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Running Inspection DataParameters to be monitored -Summary
Speed
Load
Fired Starts
Fired Hours
Site Barometric Reading
Temperatures
Inlet Ambient
Compressor Discharge
Turbine Exhaust
Turbine Wheelspace
Lube Oil Header
Lube Oil Tank
Bearing Drains
Exhaust Spread
Pressures
Compressor Discharge
Lube Pump(s)
Bearing Header
Cooling Water
Fuel
Filters (Fuel, Lube, Inlet Air)
Vibration Data for Power Train
Generator
Output Voltage
Phase Current
VARS
Load
Start-Up Time
Coast-Down Time
Field Voltage
Field Current Stator Temp.
Vibration
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4HDGT.PPT/
HYDERABAD
RUNNING INSPECTIONSOPERATIONAL DIAGNOSTICS
Start up
Increased Startup time
Jaw clutch disengagement at a lower speed
Higher vibrations during critical speeds
- Indicative of unhealthy starting means /turbine bearings
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HYDERABAD Critical speedsTypical (Fr-5P)
First critical1900 rpm
Second critical3250 rpm
Third critical5200 to 5600 rpm
Critical speedsTypical (Fr-6B)
First critical1650 to 1880 rpm
Second critical3260 to 3900 rpmThird critical7050 to 7350 rpm
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HYDERABAD Critical speedsTypical (Fr-9E)
First critical980 rpm
Second critical1300 rpm
Third critical2300 rpm
Critical speedsTypical (Fr-6FA)
First critical 1840 rpm
Second critical 4743 rpm
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HYDERABAD
RUNNING INSPECTIONSOPERATIONAL DIAGNOSTICS
Load Limitation / Hunting
Unable to maintain load
Unable to increase load
- Indicative of clogged hydraulic filters and / ordamaged fuel pump and / orrelief valve
RUNNING INSPECTIONS
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HYDERABAD
RUNNING INSPECTIONSOPERATIONAL DIAGNOSTICS
Combustion Trouble / exhaust spread
Increasing trend in exhaust temperature spread
Changing pattern of exhaust temp. spread with load
- Indicative of unequal fuel distribution tofuel nozzles
RUNNING INSPECTIONS
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HYDERABAD
RUNNING INSPECTIONSOPERATIONAL DIAGNOSTICS
Lower Loads under similar conditions
Higher Exhaust Temperature under similar
conditions
- Indicative of compressor fouling
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HYDERABAD STANDBY INSPECTION
Inspections carried out during Off-peakperiods when Unit is not running for a longduration
Check Battery system, Oil levels, instrument calibrations,replacement of various filters & servicing of accessorysystems etc.
Put the unit on ratcheting / barring gear for atleast 30 mindaily
Crank the Turbine once in a Fortnight to drive awayMoisture
Run the Gas Turbine FSNL once every month to avoidcorrosion to turbine wheel dovetails
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A Maintenance Program should:
Optimize owners maintenance costs
Maximize equipment availability
PERIODIC SHUTDOWN INSPECTIONSHYDERABAD
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Factors Affecting Maintenance Planning andMaintenance Program
Maintenance
Program
ManufacturersRecommendedMaintenance
Program
Diagnostics
Availability
Need
On-Site
Maintenance
Capability
DesignFeatures
Utilization
Need
DutyCycle
Environment
Cost ofDowntime
Type of
Fuel
Expert
Systems
Reserve
Requirements
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Case 2
1,000 Hrs/Yr
400 Starts/Yr
HGP at 3 years, not 24 years
Case 1
8,000 Hrs/Yr
160 Starts/Yr
HGP at 3 years
Because not all customers operate their gas turbines the similarl
not all customer maintenance programs are the same.
BHEL Provides Guidance for Customer Maintenance Planning
HYDERABAD
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Maintenance Cost and Equipment LifeAre Influenced by Key Service Factors
Fuel
Firing Temperature
Steam/Water InjectionCyclic Effects (Start-up rate, number of trips)
Air Quality
Service Factors Different From the Reference Condition*
Can Increase Maintenance Cost & Reduce Maintenance Intervals
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Potential Failure Modes
Continuous Duty Application Creep Deflection Creep Rupture Corrosion Oxidation Erosion. High-Cycle Fatigue.
Hot-Gas-Path Components
Cyclic Duty Application
Thermal Mechanical Fatigue Rubs/Wears.
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1HDGT.PPT/
HYDERABAD
Operation of Gas Turbine inExtended lean-lean base
mode in DLN-1 units has amaintenance factor of 10
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Maintenance Factor Definition
IDEAL INTERVAL = Interval for Continuous Base Loadon Clean Natural Gas
RECOMMENDED
INTERVAL = Ideal Interval determined fromapplication of maintenance factors
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Maintenance Factors Summary
Maintenance Requirements are Based on an IndependentCount of Hours and Starts
Certain Operating Factors Reduce Maintenance Intervals
Peak Load
Steam/Water Injection >2.2% Liquid Fuel
Trips From Load
Fast Starts
Exceeding BHEL Specification Limits can SignificantlyIncrease Maintenance Factors and Reduce Component Life
Equations for Establishing Application Specific Hot GasPath Maintenance Intervals are Available
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Exh.
Temp.
TimeStart-up Shutdown
Light-offAcceleration
Warm-up
Full SpeedNo Load
Full Speed
No Load
Load Ramp
Base Load
Fired Shutdown
Trip
Unload Ramp
Turbine Start/Stop Cycle
540 Deg C
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% Load
T
rip
Severity
Fa
ctor
01
2
3
4
5
67
8
9
10
0 20 40 60 80 100 120
Base
FSNL
For trips during Start-up
Acceleration, assume
Trip Severity Factor = 2
Maintenance Factor - Trips from Load
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Heavy-Duty Gas Turbine
CombustionHot-Gas-Path
Major
Shutdown Inspect ions
Major inspectionHot-Gas-Path
Inspection
CombustionInspection
Special Inspect ion s
Borescope
IGV Bushing insp.
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Base Line Recommended Inspection IntervalsBase Load - Gas Fuel - Dry
Factors That Can Reduce Maintenance IntervalsFuel
Load Cycle
Steam/Water Injection
Peak Load Operation
Trips from Load
Start Cycle
HGP Hardware Design
Type of
Inspection
Combustion
Hot-Gas Path
Major
Hours/Starts
12000/800
MS32/52/51
Upgrade
(Standard)
Eliminated/1200
48000/2400
8000/900
24000/900
48000/2400
12000/1200
24000/1200
48000/2400
MS6BStandard
DLN1MS6FA & 9FA
DLN2
MS9E
Standard
& DLN1
8000/450
24000/900
48000/2400
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Maintenance InspectionsCombustion Inspection - Key Elements
Foreign Objects
Abnormal Wear
Cracking
Liner Cooling Hole Plugging TBC Coating Condition
Oxidation/Corrosion/Erosion
Hot Spots/Burning
Missing Hardware
Clearance Limits
Borescope Compressor andTurbine
Potential Actions:Inspect for:Key Hardware
Combustion Liners
Combustion Covers
Fuel Nozzles
Transition PiecesCross Fire Tubes
Flow Sleeves
Check Valves
Spark Plugs
Flame Detectors
Flex Hoses
Repair/Refurbishment
Liners
Cracking/Erosion/Wear
TBC Repair
Transition PiecesWear
TBC Repair
Distortion
Fuel Nozzles
Plugging
Erosion/Wear
Cross Fire TubesWear/Burning
Criteria: Op. & Instr. Manual TILs
Service Engineers
Inspection
Methods: Visual
LP
Borescope
Availability of On Site
Spares Is Key to
Minimizing Downtime
WORK SCOPE:
HYDERABAD
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Maintenance InspectionsHot Gas Path Inspection - Key Elements
Foreign Objects Damage
Oxidation/Corrosion/Erosion
CrackingCooling Hole Plugging
Remaining Coating Life
Nozzle Deflection/Distortion
Abnormal Deflection/Distortion
Abnormal Wear
Missing HardwareClearance Limits
Potential Actions:Inspect for:Key Hardware
Nozzles (1,2,3)
Buckets (1,2,3)
Stator Shrouds
IGVs & Bushings
Compressor Blading
(Borescope)
Repair/Refurbishment
Nozzles
Weld Repair
Reposition
Recoat
Buckets
Strip & Recoat
Weld Repair
Blend
Criteria: Op. & Instr. Manual TILs
Service Engineers
Inspection
Methods: Visual
LP
Borescope
WORK SCOPE: Combust ion Inspect ion wo rk scope +
Availability of On Site
Spares Is Key to
Minimizing Downtime
HYDERABAD
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Maintenance InspectionsGT Major Inspection - Key Elements
Foreign Objects Damage
Oxidation/Corrosion/Erosion
Cracking
Leaks
Abnormal Wear
Missing Hardware
Clearance Limits
Potential Actions:Inspect for:Key Hardware
Compressor Blading
Turbine Wheels Dovetails
Journal and Seal Surfaces
Bearing Seals
Inlet System
Exhaust System
Repair/Refurbishment Stator Shrouds
Oxidation/Corrosion/Erosion Buckets
Coating DeteriorationFOD/Rubs/CrackingTip Shroud DeflectionCreep Life Limit
Nozzles Deterioration IGV Bushings Wear
Bearings/Seals Boring/Wear Compressor Blades
Corrosion/ErosionRubs/FOD
Criteria: Op. & Instr. Manual TILs
Service Engineers
Inspection
Methods: Visual
LP
Borescope
WORK SCOPE: Combust ion Inspect ion Work Scope +HotGas Path Inspect ion Work Scope +
Availability of On Sit
Spares Is Key to
Minimizing Downtim
HYDERABAD
E ti t d R i / R l t C l
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2HDGT.PPT/
HYDERABADEstimated Repair/ Replacement Cycles
Repair Replacement
Starts Hours
Liners CI 5CI 3CI
TPs CI 6CI 4CI
Fuel Nozzles CI 3CI 2CI
N#1,2,3 HGPI 3HGPI 3HGPIB#1 HGPI 3HGPI 2HGPI
B#2,3 HGPI 4HGPI 3HGPI
Shroud#1 HGPI 2HGPI 2HGPI
Shroud#2,3 HGPI 4HGPI 3HPGI
Typical and informative only. Depends upon GT type and size
R i / R l t C l Lif E t i
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2HDGT.PPT/
HYDERABAD
FIRST STAGE NOZZLE WEAR - PREVENTIVE MAINTENANCELIFE EXTENSION
Repair/ Replacement CyclesLife Extension
Without repair
Repaired Nozzle
Min AcceptabilityStandard
NozzleCondition
Severe Deterioration
New Nozzle
Acceptance Standard
First repair
2nd repair
3rd repairRepaircostexceeds
replacementcost
10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000
Operating Hours
SPARE PARTS PLANNING CONSIDERATIONS
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3HDGT.PPT/
HYDERABADSPARE PARTS PLANNING - CONSIDERATIONS
Repair / replacement intervals
Cost
Procurement cycle time
Repair cycle time Vs. Inspection down time
Shelf life
Storage facilities
Environment
Transport facilities
Borescope Inspection
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3HDGT.PPT/
HYDERABAD Borescope Inspection
BORESCOPE INSPECTION CRITERIAACCESS AREA INSPECT FOR
Compressor Blades Foreign object damage
Dirt buildup
Corrosion
Tip Erosion
Trailing Edge thinning
Stator blade root erosion
Tip clearances
Borescope Inspection
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3HDGT.PPT/
HYDERABAD
BORESCOPE INSPECTION CRITERIAACCESS AREA INSPECT FOR
Combustion Carbon build-up
(Liner and transition piece) Hot spots
Cracking
Bulging
Wear
Missing metal or thermal
barrier coating
Borescope Inspection
Borescope Inspection
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3HDGT.PPT/
HYDERABAD
BORESCOPE INSPECTION CRITERIAACCESS AREA INSPECT FOR
Turbine Nozzles Foreign object damage
Corrosion
Blocked cooling holes
Cracks
Trailing edge bowing
Erosion
Burning
Borescope Inspection
Borescope Inspection
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3HDGT.PPT/
HYDERABAD Borescope Inspection
BORESCOPE INSPECTION CRITERIAACCESS AREA INSPECT FOR
Turbine buckets Foreign object damage
Corrosion
Blisters
Erosion
Cracks
Tip clearance
Missing metal
Borescope Inspection
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3HDGT.PPT/
HYDERABAD Borescope Inspection
BORESCOPE
RIGID BORESCOPE
FLEXIBLE BORESCOPE
VIGV Bushing Inspection
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3HDGT.PPT/
HYDERABAD VIGV Bushing Inspection
1. Set vanes to full open position
2. Set up dial indicator to
measure motion normal to the
vane chord. Position the
indicator to read as close to the
vane inner button as possible
3. Deflect vane in a tangentia
direction (perpendicular to the
air flow direction) to both sides
of the bushing clearance and
record full dial indicator
reading.
AirflowDirection
VIGV
VIGV in fullyOpen Position
84
DialIndicator
VIGV Bushing Inspection
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3HDGT.PPT/
HYDERABAD VIGV Bushing Inspection
DOWN TIME REDUCTION
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3HDGT.PPT/
HYDERABAD
SPECIAL DESIGN FEATURES FOR EASY MAINTENANCE
Casings are horizontally split
With upper half of casings removed, it is possible to removenozzles and inspect buckets without removing rotor
All bearing housings are horizontally split and bearings can be
replaced without removing the rotor. Large blades are moment weighed and sequenced to avoid
rebalancing of rotor after site replacement.
Components like governing components, fuel nozzles,
combustion components are mounted type for easy maintenance All major accessories are separate assemblies and are accessible
for inspection and maintenance.
DOWN TIME REDUCTION
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