Gas Turbine Maintenance

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Revision Date: 09/07/2000 Property of Power Systems University- Proprietary Information for Training Purposes Only!

Gas Turbine MaintenancePart 1

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OPERATING FACTORS AFFECTING MAINTENANCE

• The effect of maintenance factors for fuel, starts, environment and load duty cycles are cumulative.

• As the maintenance factor increases, the time between inspections and component repairs decreases and it is possible that component replacement frequency will increase.

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Key Factors Affecting Maintenance Planning

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Plant LevelTop 5 System Contributions to Downtime

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• Cyclic Effects– Effects of Startups and Shutdowns / Trips

• Firing Temperature• Fuel

– Gas, Distillate, Crude, Quality, etc...

• Water or Steam Injection• Environment

– Air Quality

• Maintenance Practices

MAINTENANCE FACTORS

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• Cyclic Effects– Fired Starts

• Normal• Fast Load• Emergency

– Stops• Normal shutdown• Trips

– >80% Load

– Load Changes

MAINTENANCE FACTORS

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• Continuous Duty Application– Creep Deflection– Oxidation – Corrosion– High-Cycle Fatigue– Rupture– Erosion– Rubs/Wear– Foreign Object Damage (FOD)

MAINTENANCE FACTORSCauses of Wear - HGP

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• Cyclic Duty Application– Thermal Mechanical Fatigue– High-Cycle Fatigue– Rubs/Wear– Foreign Object Damage (FOD)

MAINTENANCE FACTORSCauses of Wear - HGP

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Fig 41 - Page 28

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• Typical Max Inspection Intervals (MS6B/MS7EA)– Hot Gas Path Inspection 24,000 hrs or 1200 starts– Major Inspection 48,000 hrs or 2400 starts

• Criterion is Hours or Starts (Whichever Occurs First)

MAINTENANCE FACTORS

Fig 41 - Page 28

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• Hours Factors– Fuel

• Gas 1• Distillate 1.5• Crude 2 to 3• Residual3 to 4

– Peak Load 1 hr at peak = 6 hrs at base load– Water/Steam Injection

• Dry Control 1 (GTD-222)• Wet Control 1.9 (5% H2O GTD-222)

MAINTENANCE FACTORSHot Gas Path Buckets/Nozzles

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• Starts Factors– Trip from Full Load 8– Fast Load 2– Emergency Start 20

MAINTENANCE FACTORSHot Gas Path Buckets/Nozzles

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GE Maintenance Interval for Hot Gas Path Inspection

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MAINTENANCE FACTOR VS FUEL TYPE

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Bucket Life Firing Temperature Effect

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Exhaust Temperature Control CurveDry vs. Wet Control

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Turbine Start / Stop CycleFiring Temperature Changes

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First - Stage Bucket TransientTemperature Distribution

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Low Cycle Fatigue Life Sensitivities1st Stage Bucket

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Maintenance FactorTrips From Load

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Maintenance Interval = 24000 (Hours) Maintenance FactorWhere:

Maintenance Factor = Factored Hours / Actual Hours

Factored Hours = (K + M * I) * (G + 1.5D + AfH + 6P) Actual Hours = (G + D + H + P)

G = Annual Base Load Operating Hours on Gas FuelD = Annual Base Load Operating Hours on Distillate FuelH = Annual Operating Hours on Heavy FuelAf = Heavy Fuel Severity Factor (Residual Af = 3 to 4, Crude Af = 2 to 3)P = Annual Peak Load Operating HoursI = Percent Water/Steam Injection Referenced to Inlet Air FlowM & K = Water/Steam Injection Constants

MAINTENANCE FACTORSHours Based Hot Gas Path

MF =

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Maintenance Interval = 1200 (Starts) Maintenance FactorWhere:

Maintenance Factor = Factored Starts / Actual Starts η Factored Starts = (0.5NA + NB + 1.3NP + 20E + 2F + Σ aT1 T1) i=1 Actual Starts = (NA + NB + NP + E + F + T)

NA = Annual Number of Part Load/Stop Cycles (<60% Load)NB = Annual Number of Normal Base Load Start/Stop CyclesNP = Annual Number of Peak Load Start/Stop CyclesE = Annual Number of Emergency StartsF = Annual Number of Fast Load StartsT = Annual Number of TripsaT = Trip Severity Factor = f (Load)n = Number of Trip Categories (I.e., Full Load, Part Load, etc.)

MAINTENANCE FACTORSStarts Based Hot Gas Path

MF =

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• Operation of the combustion gas turbine, as any rotating power equipment, must include a planned program of periodic inspection.

• With accompanying repair and replacement of parts as required, will ensure the maximum availability and reliability of the turbine.

GAS TURBINE MAINTENANCE

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OBJECTIVE OF THE GAS TURBINE MAINTENANCE SECTION

• Describe the inspections and the action to be taken.• Identify the components and parts that should be

examined.• Discuss the Inspection and Maintenance Manual• Pre-Inspection Items• Standard Practice Review

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OPERATING FACTORS AFFECTING MAINTENANCE

• The effect of maintenance factors for fuel, starts, environment and load duty cycles are cumulative.

• As the maintenance factor increases, the time between inspections and component repairs decreases.

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• Type of Fuel• Starting Frequency• Load Cycle and Firing Temperature• Water or Steam Injection• Environment• Maintenance Practices

MAINTENANCE FACTORS

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• Running Inspections– Startup– Operating

• Shutdown Inspections– Combustion– Hot Gas Path– Major

• Standby Inspections– Checking of Batteries, Filters, Oil and Water Levels, etc…

• Special Inspections– Borescope

TYPES OF INSPECTIONS

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• Keep a record of the inspections made, and the maintenance work performed.

• It is expected that a maintenance program will start with minor work, and increase in magnitude over a period of time to a major overhaul.

• Optimized inspections will reduce unit outage time and maintenance cost.


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• Parts condition information data• Initial inspection planning• Good maintenance planning for minimum down time

requires the availability of replacement parts.• Minimum stock of repair parts in a predetermined

location.• Anticipate needs during outages.

MAINTENANCE PRACTICES

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• Clean the compressor per the gas turbine Water Wash.• A complete set of operating data including vibration

readings should be taken and recorded for reference.• Inventory and Inspection of tooling.• General walk around inspection prior to tear down.• Lock Out / Tag Out (LOTO)

PRIOR TO GAS TURBINE MAINTENANCE

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GAS TURBINE COMPRESSOR CLEANING

• The Gas Turbine Water Wash System will be covered in a separate lecture.

• Gas Turbines operating with Dry Low Nox Combustion Systems should not use solid compounds for compressor cleaning.

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INSPECTION AND MAINTENANCE MANUALS

• Notes:– Highlights an essential element of a procedure to assure

correctness.

• Caution:– Indicates a procedure or practice, which if not strictly

observed, could result in damage or destruction of equipment.

• Warning:– Indicates a procedure or practice, which could result in

injury to personnel of loss of life if not followed correctly.

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• Introduction• Standard Practices• Auxiliary and Controls Systems Maintenance• Scheduled Turbine Maintenance• Combustion Inspection• Hot Gas Path Inspection• Major Inspection• Maintenance Inspection Forms

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• Introduction– General– Operating Factors Affecting Maintenance– Maintenance Practices– Types of Inspection– Inspection Intervals– Special Inspection

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• Standard Practices– General– Recommended Solvents, Sealers and Cleaners– Lubrication Guidance– Gas Turbine Compressor Cleaning– Tools and Equipment– Special Tools– Ordering Renewal Parts, Repair and Replacement parts– Returning Turbine Parts for Repair / Replacement– Maintenance Parts Recommendations


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LUBRICATION GUIDANCE

• Lubrication frequency will vary, depending on turbine hours and ambient temperature.

• It is suggested that records on lubrication intervals be kept to determine variances between periods listed on the chart and those scheduled for a specific installation.

• Lubricants listed do not exclude comparable products from other oil companies.

• Use of alternate lubricants must be approved by component manufacture.

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• Spare and renewal part orders for General Electric turbines should be placed with your General Electric Company Representative Operations Office.

• Parts which form one complete working unit must be ordered together.

• Any new safety features and design improvements are usually incorporated in replacement parts.

ORDERING RENEWAL, REPAIR AND REPLACEMENT PARTS

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ORDERING RENEWAL, REPAIR AND REPLACEMENT PARTS

• If no drawing, parts list or reference publication is available for a part, a sketch or sample of the item, together with all necessary dimensions and description of the parts function, should accompany the order.

• Store parts in a suitable place to prevent loss or damage.

• Coat all finished iron or steel surfaces with oil or other suitable compound to protect them for corrosion.

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RETURNING PARTS FOR REPAIR OR REPLACEMENT

• Contact your General Electric Company Representative Operations Office for assistance when returning turbine parts to GE.

• They will supply you with proper procedures as well as supply the required packing instructions, packing lists and shipping labels.

• A GE representative can be directed to confirm receipt of your parts and explain factory corrective action recommendations.

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MAINTENANCE PARTS RECOMMENDATIONS

• Spare parts recommendations are provided to support scheduled combustion, hot gas path and major inspections.

• Spare parts listings must be used in conjunction with the Parts List and Drawings Volume of the Service Manual.

• Use the typical spare parts list as a guide, your spare parts stock should be reviewed at a pre-inspection planning meeting.

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• Auxiliary and Controls Systems Maintenance– Periodic Inspection Schedule– Inspection and Maintenance Procedures

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• Scheduled Turbine Maintenance– Running Inspections– Housekeeping– Data Recording– Special Inspections


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• Combustion Inspection• Hot Gas Path Inspection• Major Inspection

– Disassembly– Inspection– Re-assembly– Startup Checks

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GAS TURBINE BORESCOPE

• Incorporates the use of the optical borescope.• Allows rapid inspection of the following areas:

– Turbine Section– Axial Flow Compressor– Combustion System

• Removal of spark plugs and flame detectors from combustion system allows access to these areas.

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GAS TURBINE BORESCOPE INSPECTION CRITERIA

• Compressor Blades:– FOD and DOD– Dirt Build Up– Corrosion– Tip Erosion– Trailing Edge Thinning– Stator Blade Root Erosion– Tip Clearance

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• Combustion, (Liner and Transition Piece):– Carbon Build-Up– Hot Spots– Cracking– Bulging– Wear– Missing Metal

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• Turbine Nozzles:– FOD and DOD– Corrosion– Blocked Cooling Holes– Cracks– Trailing Edge Bowing– Erosion– Burning

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• Turbine Buckets:– FOD and DOD– Corrosion– Blisters– Cracks– Tip Clearance– Erosion– Missing Metal

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1. Set vanes to the full open position.

2. Set up dial indicator to measure motion normal to the vane cord. Position the indicator to read as close to the vane inner button as possible.

3. Deflect vane in a tangential direction (perpendicular to the air flow direction) to both sides of the bushing clearance and record full dial indicator reading.

Dial IndicatorBushing

AirflowDirection

VIGV in fullyopen position

1

2

3VIGV

VIGV BUSHING INSPECTION

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Frame Size VIGV Type 1

Bushing 2

Clearance Limitsfor Bushing

Changeout (>= inches)Inspection Interval

(Hours)

MS5001, MS5002, MS6001**Pre Model FA

403 Stainless403 Stainless

GTD 450

158A7888P004/5/6315A9681 or 339A9913315A9681 or 339A9913

0.0500.0500.075

5,0008,000

16,000 3 8,000

4

MS6001FA GTD 450 339A9913 0.075 16,000 3

8,000 4

MS7001*, MS9001**Pre Model F

403 Stainless403 Stainless

GTD 450

158A7888315A9681 or 339A9913315A9681 or 339A9913

0.0700.0700.100

8,0008,000

16,000 3

8,000 4

MS7001F/FA/FA+ GTD 450 339A9913 0.100 16,000 3

8,000 4

MS9001F/FA GTD 450 328A7020 0.100 16,000 3

8,000 4

Note 1: For unit specific drawing number identification, refer to Model List Item 1301Note 2: For unit specific drawing number identification, refer to Model List Item 0811Note 3: Nominal Base Load IGV angle of 84º or LowerNote 4: Nominal Base Load IGV angle greater than 84º (i.e. 86º or 88º)

VIGV BUSHING INSPECTION SCHEDULE

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Gas Turbine Maintenance