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Gas turbine maintenance
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Heavy-Duty Gas Turbine Operating
and Maintenance Considerations
2HDGT.PPT/
GT INSPECTIONS
• Running Inspections
• Standby Inspections
• Shutdown Inspections
3HDGT.PPT/
RUNNING INSPECTIONS PRE START UP CHECKS
• AC Lube Oil Pumps “ON”on Auto
• Ratcheting / Barring is OK.
• EOP is tested
• All MCC modules are switched ‘ON’ and are kept on ‘AUTO’
• Cooling Water level is OK
• Lube Oil Level is OK & Oil temp. normal
• Visual Inspection of Machine is OK
4HDGT.PPT/
RUNNING INSPECTIONS CHECKS DURING STARTUP
• Flame is sensed in all Flame Scanners
• Exhaust Temperatures are uniform and Spread is normal
• Acceleration is Smooth and Time taken is in line with earlier
values
• Rise in Exhaust Temperature is Uniform
• Exhaust Temperature profile is OK and Spread Values are
within Limits
5HDGT.PPT/
• Rise in Wheelspace Temperature is Uniform
• Vibrations are within Limits and as per earlier values
• Bearing Oil Drain Temperatures are Normal
• Opening of Jaw Clutch (Not applicable for Fr9E & Fr6FA) is
at approx. at the same Speed as earlier
RUNNING INSPECTIONS CHECKS DURING STARTUP CONTD.
6HDGT.PPT/
RUNNING INSPECTIONS PARAMETERS TO MONITOR
Pressure
Lube OilHydraulic OilTrip OilComp. DischargeInlet Air Filter DPCooling water
Temperatures
Lube Oil HeaderBrg. DrainsComp. InletComp. DischargeExhaustWheelspaceCooling Water Outlet
7HDGT.PPT/
OTHERS
VibrationsNoise, RubsStartup TimeCoast Down TimeFired StartsFired Hours
GENERATOR
VoltageCurrentLoadStator Temperatures
RUNNING INSPECTIONS PARAMETERS TO MONITOR-CONT’D
Operating Inspection Data Parameters -Summary
SpeedLoadFired StartsFired HoursSite Barometric ReadingTemperatures
Inlet AmbientCompressor DischargeTurbine ExhaustTurbine WheelspaceLube Oil HeaderLube Oil TankBearing DrainsExhaust Spread
Pressures– Compressor Discharge– Lube Pump(s)– Bearing Header– Cooling Water– Fuel– Filters (Fuel, Lube, Inlet Air)
Vibration Data for Power TrainGenerator
– Output Voltage – Phase Current– VARS– Load
Start-Up TimeCoast-Down Time
– Field Voltage– Field Current– Stator Temp.– Vibration
9HDGT.PPT/
RUNNING INSPECTIONS OPERATIONAL DIAGNOSTICS
Start up
Load Hunting
Combustion Trouble / exhaust spread
Lower Loads
Higher Temperatures
10HDGT.PPT/
STANDBY INSPECTION
Inspections carried out during Off-peak periods when Unit is not running
• Check Battery system, Oil levels, instrument calibrations, replacement of various filters & servicing of accessory systems etc.
• Crank the Turbine once in a Fortnight to drive away Moisture
A Maintenance Program should:
Optimize owner’s maintenance costs
Maximize equipment availability
PERIODIC SHUTDOWN INSPECTIONS
Factors Affecting Maintenance Planning and Maintenance Program
MaintenanceProgram
MaintenanceProgram
ManufacturersRecommended
MaintenanceProgram
ManufacturersRecommended
MaintenanceProgram
DiagnosticsDiagnostics
AvailabilityNeed
AvailabilityNeed
On-SiteMaintenance
Capability
On-SiteMaintenance
Capability
DesignFeaturesDesign
Features
UtilizationNeed
UtilizationNeed
DutyCycleDutyCycle
EnvironmentEnvironment
Cost ofDowntimeCost of
Downtime
Type ofFuel
Type ofFuel
ExpertSystemsExpert
Systems
ReserveRequirements
ReserveRequirements
Case 2
1,000 Hrs/Yr400 Starts/Yr
HGP at 3 years, not 24 years
Case 1
8,000 Hrs/Yr160 Starts/Yr
HGP at 3 years
Because not all customers operate their gas turbines the similarly
not all customer maintenance programs are the same.
BHEL Provides Guidance for Customer Maintenance Planning
Maintenance Cost and Equipment Life Are Influenced by Key Service Factors
FuelFiring TemperatureSteam/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
Service Factors Different From the Reference ConditionService Factors Different From the Reference Condition**Can Increase Maintenance Cost & Reduce Maintenance IntervalsCan Increase Maintenance Cost & Reduce Maintenance Intervals
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.
Maintenance FactorsHot Gas Path (Buckets & Nozzles)
Typical Max Inspection Intervals (MS6B/Ms7EA)Hot Gas Inspection 24,000 hrs or 1200 StartsMajor Inspection 48,000 hrs or 2400 Starts
Criterion is Hours or Starts (Whichever Occurs First)
Hours Factors
FuelGas 1Distillate 1.5Crude 2 to 3Residual 3 to 4
Peak Load 6Water/Steam Injection
Dry Control 1 (GTD-222)Wet Control 1.9 (5% H20)
Factors Impacting Maintenance
Starts Factors
Trip From Full Load 8Fast Load 2Emergency Start 20
17HDGT.PPT/
Operation of Gas Turbine in Extended lean-lean base mode in DLN-1 units has a maintenance factor of 10
Maintenance Factor Definition
IDEAL INTERVAL = Interval for Continuous Base Load on Clean Natural Gas
RECOMMENDEDINTERVAL = Ideal Interval determined from
application of maintenance factors
Maintenance Factors Summary
Maintenance Requirements are Based on an Independent Count of Hours and StartsCertain Operating Factors Reduce Maintenance Intervals
Peak LoadSteam/Water Injection >2.2%Liquid FuelTrips From LoadFast Starts
Exceeding BHEL Specification Limits can Significantly Increase Maintenance Factors and Reduce Component Life Equations for Establishing Application Specific Hot Gas Path Maintenance Intervals are Available
Estimated Effect of Fuel Type on Maintenance
Residual
MaintenanceFactor
Distillates
HeavyLight
Natural Gas
7 8 9 10 11 12 13 14 15
Fuel Percent Hydrogen by Weight in Fuel20
Exh.Temp.
TimeStart-up Shutdown
Light-offAcceleration
Warm-up
Full SpeedNo Load
Full SpeedNo Load
Load Ramp
Base Load
Fired ShutdownTrip
Unload Ramp
Turbine Start/Stop Cycle
540 Deg C
% Load
Trip
Sev
erity
Fac
tor
0123456789
10
0 20 40 60 80 100 120
Base
FSNL
For trips during Start-upAcceleration, assume Trip Severity Factor = 2
Maintenance Factor - Trips from Load
Heavy-Duty Gas Turbine
CombustionHot-Gas-PathMajor
Shutdown Inspections
Major inspectionHot-Gas-Path
InspectionCombustionInspection
Special Inspections
BorescopeIGV Bushing insp.
Base Line Recommended Inspection Intervals Base Load - Gas Fuel - Dry
Factors That Can Reduce Maintenance IntervalsFuelLoad CycleSteam/Water InjectionPeak Load Operation
Trips from LoadStart CycleHGP Hardware Design
Type ofInspection
Combustion
Hot-Gas Path
Major
Hours/Starts
12000/800
MS32/52/51 Upgrade (Standard)
Eliminated/1200
48000/2400
8000/900
24000/900
48000/2400
12000/120024000/1200
48000/2400
MS6BStandard& DLN1
MS6FA & 9FA DLN2
MS9EStandard& DLN1
8000/450
24000/900
48000/2400
Maintenance Inspections Combustion Inspection - Key Elements
Foreign ObjectsAbnormal WearCrackingLiner Cooling Hole PluggingTBC Coating ConditionOxidation/Corrosion/ErosionHot Spots/BurningMissing HardwareClearance LimitsBorescope Compressor and Turbine
Potential Actions:Potential Actions:Potential Actions:Inspect for:Inspect for:Inspect for:Key HardwareKey HardwareKey Hardware
Combustion LinersCombustion CoversFuel NozzlesTransition PiecesCross Fire TubesFlow SleevesCheck ValvesSpark PlugsFlame DetectorsFlex Hoses
Repair/Refurbishment Liners
Cracking/Erosion/Wear TBC Repair
Transition Pieces WearTBC RepairDistortion
Fuel NozzlesPluggingErosion/Wear
Cross Fire TubesWear/Burning
Criteria:Criteria: Op. & Instr. ManualOp. & Instr. ManualTIL’sTIL’sService EngineersService Engineers
Inspection Inspection Methods:Methods:
VisualVisualLPLPBorescopeBorescope
Availability of On SiteAvailability of On SiteSpares Is Key to Spares Is Key to
Minimizing DowntimeMinimizing Downtime
WORK SCOPE:WORK SCOPE:
Maintenance Inspections Hot Gas Path Inspection - Key Elements
Foreign Objects DamageOxidation/Corrosion/ErosionCrackingCooling Hole PluggingRemaining Coating LifeNozzle Deflection/DistortionAbnormal Deflection/DistortionAbnormal WearMissing HardwareClearance Limits
Potential Actions:Potential Actions:Potential Actions:Inspect for:Inspect for:Inspect for:Key HardwareKey HardwareKey Hardware
Nozzles (1,2,3)
Buckets (1,2,3)
Stator Shrouds
IGV’s & Bushings
Compressor Blading(Borescope)
Repair/Refurbishment Nozzles
Weld RepairRepositionRecoat
BucketsStrip & RecoatWeld RepairBlend
Criteria:Criteria: Op. & Instr. ManualOp. & Instr. ManualTIL’sTIL’sService EngineersService Engineers
Inspection Inspection Methods:Methods:
VisualVisualLPLPBorescopeBorescope
WORK SCOPE: Combustion Inspection work scope +WORK SCOPE: Combustion Inspection work scope +
Availability of On SiteAvailability of On SiteSpares Is Key to Spares Is Key to
Minimizing DowntimeMinimizing Downtime
Maintenance Inspections GT Major Inspection - Key Elements
Foreign Objects DamageOxidation/Corrosion/ErosionCrackingLeaksAbnormal WearMissing HardwareClearance Limits
Potential Actions:Potential Actions:Potential Actions:Inspect for:Inspect for:Inspect for:Key HardwareKey HardwareKey Hardware
Compressor Blading
Turbine Wheels Dovetails
Journal and Seal Surfaces
Bearing Seals
Inlet System
Exhaust System
Repair/RefurbishmentStator Shrouds
Oxidation/Corrosion/ErosionBuckets
Coating DeteriorationFOD/Rubs/CrackingTip Shroud DeflectionCreep Life Limit
Nozzles DeteriorationIGV Bushings WearBearings/Seals Boring/WearCompressor Blades
Corrosion/ErosionRubs/FODCriteria:Criteria: Op. & Instr. ManualOp. & Instr. Manual
TIL’sTIL’sService EngineersService Engineers
Inspection Inspection Methods:Methods:
VisualVisualLPLPBorescopeBorescope
WORK SCOPE: Combustion Inspection Work Scope + WORK SCOPE: Combustion Inspection Work Scope + HotHot––Gas Path Inspection Work Scope +Gas Path Inspection Work Scope +
Availability of On SiteAvailability of On SiteSpares Is Key to Spares Is Key to
Minimizing DowntimeMinimizing Downtime
28HDGT.PPT/
Estimated Repair/ Replacement CyclesRepair Replacement
Starts Hours
Liners CI 5CI 3CI
TPs CI 6CI 4CI
Fuel Nozzles CI 3CI 2CI
N#1,2,3 HGPI 3HGPI 3HGPI
B#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
29HDGT.PPT/
FIRST STAGE NOZZLE WEAR FIRST STAGE NOZZLE WEAR -- PREVENTIVE MAINTENANCE PREVENTIVE MAINTENANCE –– LIFE EXTENSION LIFE EXTENSION
Repair/ Replacement Cycles – Life Extension
30HDGT.PPT/
SPARE PARTS PLANNING - CONSIDERATIONS
• Repair / replacement intervals
• Cost
• Procurement cycle time
• Repair cycle time Vs. Inspection down time
• Shelf life
• Storage facilities
• Environment
• Transport facilities
31HDGT.PPT/
Borescope Inspection
32HDGT.PPT/
Borescope Inspection
33HDGT.PPT/
Borescope Inspection
BORESCOPE
RIGID BORESCOPE
FLEXIBLE BORESCOPE
34HDGT.PPT/
VIGV Bushing Inspection
35HDGT.PPT/
VIGV Bushing Inspection
36HDGT.PPT/
SPECIAL DESIGN FEATURES FOR EASY MAINTENANCE• Casings are horizontally split
• With upper half of casings removed, it is possible to remove nozzles and inspect buckets without removing rotor
• All bearing housings are horizontally split and bearings can bereplaced 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 accessiblefor inspection and maintenance.
DOWN TIME REDUCTION