Gas Turbine Technology

gGE Power Systems

Gas Turbine RepairTechnology

K.J. PallosGE Energy Services TechnologyAtlanta, GA

GER-3957B

Contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Operation and Maintenance Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Repair vs. Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Component Repairs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Nozzles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Stage One Nozzle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Activated Diffusion Healing: Distortion-Free Nozzle Restoration . . . . . . . . . . . . . . . . . . . . . . . 5Nozzle Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Stages Two and Three Nozzle Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Advanced Bucket Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Rotors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Combustion Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Combustor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Transition Pieces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Fuel Nozzles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Component Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Extendor™ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Compressor Corrosion Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Turbine Corrosion/Oxidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Thermal Barrier Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Service Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Appendix — Destructive Analysis: A Tool for Understanding Component Life . . . . . . . . . 21

GE Meeting Industry’s Demands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Material Issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Limitations of Non-Destructive Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21The Need for Destructive Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Benefits of Destructive Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Customer Satisfaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Find Out More . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Gas Turbine Repair Technology

GE Power Systems ■ GER-3957B ■ (04/01) i


GE Power Systems ■ GER-3957B ■ (04/01) ii

AbstractUnit availability and effective utilization ofmaintenance funds are two of the most impor-tant concerns of a gas turbine owner/operator.Major gas turbine components have limitedlives in comparison to the unit’s useful life.Owners/operators are continually faced withdecisions regarding component replacementand/or repair. A component repair programthat minimizes maintenance costs and maxi-mizes equipment availability can be institutedwithin the installed base to meet or improve fi-nancial objectives. This paper summarizes someof the state-of-the-art gas turbine component re-pair processes developed by GE to support thefleet of GE-designed heavy-duty gas turbines.

Operation and MaintenanceConsiderations GE’s recommended operating and mainte-nance practices are discussed in the publica-tion, “Heavy-Duty Gas Turbine Operating andMaintenance Considerations” (GER-3620G).This paper discusses the factors that influenceequipment life. These life-limiting factors mustbe understood and accounted for in theowner’s maintenance plans (Table 1).

Each one of these factors has an effect on gasturbine maintenance intervals and componentparts’ lives and will vary depending on eachunit’s operation. Some of the potential and typ-ical failure modes for hot gas path componentsin continuous and cyclic-duty machines are list-ed in Table 2.

Thermal mechanical fatigue is the predomi-nant life limiting factor for peaking machines,while creep, oxidation and corrosion are thedominant limiters for continuous-duty ma-chines. GER-3620G discusses these limiting fac-tors in detail and provides criteria for establish-

ing maintenance inspection intervals. Thescope of typical maintenance inspections (com-bustion, hot gas path and major) are outlinedthere and estimated repair and replacement cy-cles are provided for some major components.

Repair vs. Replacement Once a maintenance plan is established, theowner/operator implements it. The mainte-nance cycle starts with the pre-outage planning,continues through the outage, and ends withthe post-outage assessment. As one would ex-pect, most gas turbine components have a finitelife or expected life in the turbine under the GEperformance guidelines. (See Table 3.) Duringthe maintenance or outage cycle, owners andoperators decide to use the component “as is,”repair the component, or replace the compo-nent. This post-outage assessment provides thebasis for planning the next outage.Throughout this outage process, the owner/operator will be faced with many difficult deci-sions that will determine unit reliability, mainte-nance costs, and operating benefit.

• Fuel

• Firing Temperature

• Steam/Water Injection

• Cyclic Effects

Since GE is continually improving gas turbinetechnology and applying it to component de-signs that can be retrofitted in older units, theowner can evaluate the economics associatedwith upgrading or uprating the unit by replacingone or more components with state-of-the-artcomponents. GE can consult in various mannersby contacting a Customer Service or ProductService specialists. One can also perform some


Table 1. Major life limiting factors

GE Power Systems ■ GER-3957B ■ (04/01) 1

preliminary studies on which direction to take by looking on GE’s web page,www.gepower.com, under the Turbine Op-timizer.

• Continuous Duty- Rupture- Creep Deflection- High-Cycle Fatigue- Oxidation- Erosion- Corrosion- Rubs/Wear- Foreign Object Damage

• Cyclic Duty- Thermal Mechanical Fatigue- High-Cycle Fatigue- Rubs/ Wear- Foreign Object Damage

There exist several models that operators mayincorporate to make the prime feasibility deci-

sion between the component replace, uprate orrepair scenario. Typical gas turbine componentdamage that occurs during usage includes com-ponent cracking, foreign object damage(FOD), oxidation and corrosion. In many cases,the component’s condition at any given inspec-tion can be anticipated by the unit’s perform-ance. The damage may be obvious and thescope of repair may be relatively straightfor-ward. Of course, a replace/repair decision mustbe based on situational specifics. For example, aset of coated buckets with high operationalhours showing signs of wear may be mechani-cally repaired without recoating and allowed torun to the end of its remaining life. In this par-ticular instance, recoating of the buckets wasnot a cost-effective option.

Some damage will not be detectable through vi-sual observation. Accurate dimensional checkand non-destructive examinations (NDE) tech-niques like flourescent penetrant inspectionmay reveal additional discontinuities, such asstress cracking, that require more extensive re-pairs (Figure 1). Additionally, on airfoils where



Table 3. Turbine component life flowchart

Table 2. Potential failure modes – hot gas pathcomponents

Gas Turbine Component Life Diagram with Key Factors

Assembly TurbineOperation Outage

Assembly

TurbineOperation Outage

Assembly

RepairWorkscope

RepairWorkscope

Stores

Stores

Continue Cycleto Turbine Life

DesignMaterials

ConfigurationCombustion

Rotor

Customer ConditionDesign Status

Upgrade Potential

New PartsPrevious Repaired

PartsCompetitors

Repaired PartsContinued Parts

No uprate desired

FuelPower Level

Firing TemperatureOperation Type

CombustionConfiguration

FuelPower Level

Firing TemperatureOperation Type

CombustionConfiguration

Inspect by Service Center

Inspect by Service Center

Inspect at Site

Inspect at Site

Uprate

Uprate

internal defects can hide, destructive sampleanalysis can provide valuable information aboutthe set component condition and the repairworkscope. For example, it enables the charac-terization of internal cooling passage micro-structure, which may differ from the behaviorof the external material. In addition, crackdepths can be accurately determined.Furthermore, the information gathered duringdestructive analyses can be studied togetherwith the gas turbine running conditions to helpidentify critical operating parameters. The cus-tomer is thereby able to optimize future operat-ing conditions for enhanced performance, aswell as improve the prediction of future repairprocess schedules on the hardware.

A complete repair scope is determined onlyafter rigorous analysis of all inspection data. It isinteresting to note that not all serviced or dam-aged components are candidates for repair.Some components are damaged beyond GE-prescribed repair limits. Since all gas turbinecomponents have a finite life, the cost of repair

or replacement and the component’s future lifeexpectancy are integrated into the engineeringrepair recommendations.

Component RepairsWith new technologies being implemented inthe gas turbine world, component repair is anever-changing challenge.

The effort toward increased operating efficien-cy and decreased heat rate requires that re-paired components conform closely with origi-nal equipment manufacturer’s (OEM) drawingrequirements and specifications. With that inmind, the need for consistent repair practicesthroughout the service organization has be-come a top company priority. The sharing ofpiece-part qualifications, best practices, process-es and procedures, fixtures and tooling has be-come more critical than ever.

Each repair is engineered to provide the cus-tomer with maximum benefit while balancingcost and cycle times. A multi-organizational en-gineering review and approval process is re-quired by the GE Service Centers before a newrepair is implemented. This ensures that criticaldesign and life-enhancing features are checkedand re-checked. Each service center documentsa new repair in a Manufacturing Process Plan(MPP). This outlines the repair procedures and“freezes” the process so that the repairs are ro-bust and reproducible. GE’s internal audit teamreviews each package and requires rigorous test-ing before approval and release is issued. Theseprocedures are in keeping with the ISO 9000standards embraced by GE and its repair organ-izations.

Nozzles

Stage One Nozzle There are several nozzle failure modes associat-ed with the high temperature environment of



Figure 1. Stress cracked bucket

industrial gas turbines. These can be catego-rized under creep, thermal fatigue, oxidation,incipient melting and many forms of mechani-cal damage. Each failure mode presents differ-ent requirements for component repair.

Nozzles that are candidates for repair undergoan initial metallurgical evaluation. From theseresults, engineering recommendations aremade on the nozzle’s continued serviceability.The reparability and/or weldability of the noz-zle and the required repair methods and opera-tions are determined.

First, a triangle-shaped specimen is cut from thepartition’s trailing edge (Figure 2). It is mount-ed and polished for metallurgical evaluation(specimen “MetLab”). The metallurgical analy-sis includes microstructural evaluations of the“as-received” and “heat-treated” conditions, andobservations of intergranular oxidation (IGO),chromium migration (CM), chromium deple-tion (CD), carbide precipitates (CP) and wallthickness. Figure 3 shows a typical nozzle cool-ing hole with chrome depletion and oxidation,as indicated by the lighter contrast regions onthe specimen’s external surfaces.

Specimens may be taken from up to 10 par-titions. The specimens are taken from the noz-zle segment partition which is closest to the cen-ter of each adjacent transition piece. This cen-ter area experiences the highest temperatures

and reflects the nozzle’s most severe operatingconditions. Sidewall specimens may also betaken for evaluation if the nozzle has large areasof distress. If the MetLab inspected partition in-dicates a severe metallurgical problem, addi-tional samples are taken on adjacent partitionsto determine the extent of the distress.

The primary method of dimensional restora-tion to the nozzle is weld repair. To enhanceand improve weld repair life, an advanced fillermaterial was developed for repair of cobalt base(X-40, X-45 and FSX-414) investment cast noz-zle segments. This material breakthrough wasaccomplished with the patented creation ofNozzaloy™. Nozzaloy™ repairs can also be ap-plied over previously applied ActivatedDiffusion Healing (ADH) repairs.



Figure 2. Trailing edge specimen

Figure 3. Metallurgical evalution showing chromedepletion/oxidation

Figure 4. Nozzaloy™ repair over ADH

A metallurgical evaluation of such a Nozzaloy™repair (Figure 4) demonstrates its ability to forma sound bond and contamination-free inter-face. Nozzaloy™ extends repair intervals by in-hibiting crack initiation by a factor greater thanfour when compared to those filler metal alloysmore commonly used in the industry.Nozzaloy™ not only shows the highest resis-tance to crack initiation, but the crack propaga-tion rate is also as low as the base metal. (SeeFigure 5 and Figure 6.)

Activated Diffusion Healing: Distortion-Free Nozzle Restoration Activated Diffusion Healing (ADH) is a uniquerepair method used in nozzle restoration. Theprocess deposits a metallurgically sound propri-etary alloy combination to a nozzle substrate for

minor and major repairs on hot gas path sur-faces. A key attribute of ADH is that it causes noparts distortion during application and high-temperature processing. This technique wasoriginally developed by GE’s Aircraft Enginegroup for vane (nozzle) repair. GE PowerSystems’ Inspection and Repair Services (I&RS)has modified the process for use with heavy-duty industrial gas turbine alloys.

ADH lends itself to nozzle surface erosionrestoration, craze crack repair and replacementof trailing edge metal loss. Typical erosion dam-age of a nozzle sidewall that is readily repairedwith ADH is shown in Figure 7.

The ADH process uses a mixture of superalloypowders and an organic binder tailored to meetthe part’s specific design requirements. Themixture of ADH materials is designed to melt,solidify and diffuse when placed through a con-trolled thermal cycle in a vacuum furnace. ADHcomponents produce a liquid which iso-thermally resolidifies, thus avoiding undesirableeutectic phases. With further thermal treat-ment, ADH repairs closely approach the com-position, microstructure and properties of theparent metal. (See Figure 8.)

The ADH alloy system selected for nozzle re-pairs is compatible with previous repair weld-ments and is readily weldable. (See Figure 4.) Keymechanical test data acquired for comparison



CRACK INITIATION & GROWTH CURVES

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300 350 400 450 500

NUMBER OF CYCLES

CRACK

LENGTH PROPAGATION

FACTORS

L - 605(WELDMENT)

NOZZALOY

FSX - 414 BASEMATERIAL

Figure 5. Nozzaloy™ crack initiation

Figure 7. Nozzle requiring ADH repair

THERMAL FATIGUE CHARACTERISTICS

20

300

310

0

50

100

150

200

250

300

350

L - 605 (WELDMENT) NOZZALOY FSX - 414 BASE MATERIAL

MATERIAL

NUMBER OF CYCLESTO CRACK INITIATION

Figure 6. Nozzaloy™ thermal fatigue characteristics

with base metal properties indicates that ADH-repaired nozzle trailing edges perform favor-ably. ADH is applied either in a preformedshape or as a slurry. In Figure 9, a GE I&RS re-pair technician uses a slurry-filled syringe toapply ADH to specific areas of a nozzle’s side-wall.

Nozzle Modifications An additional advanced repair offering in-cludes a redesign and modification of nozzlecooling holes. Cooling hole upgrades directlyimprove the service life of investment cast noz-zle segments by enhancing film cooling effec-tiveness and reducing thermal-mechanical fa-tigue. These changes are implemented on thenozzle’s leading edge, pressure side, trailingedge and outer sidewall.

Modification of cooling holes on pressure sideairfoils and trailing edges is also accomplishedwith “wishbone coupon” replacements. Wish-bone coupons provide improved cooling effec-tiveness and replace distressed airfoil materialwith new cast material. Foreign object damageof a nozzle’s aft chord is also easily remediedwith wishbone coupon replacements.

Another opportunity to improve a nozzle’s effi-ciency during repair and refurbishment is tomodify the inner support ring and outer retain-ing ring sealing surfaces. This is known as achordal hinge modification and it results in areduction in compressor discharge air leakagearound the stage one nozzle. To accomplish thismodification, a weld build-up is applied to theinner contact area on each segment and a newsealing surface rib is machined into the nozzlesegments. A modification is also made to theflat seals which bear on the retaining ringagainst the stage one shroud blocks.

Stages Two and Three Nozzle Repair Stage two and three nozzles are of a cantile-vered design. They are supported from theouter wall by a series of hook fits to the shroudblocks to the turbine shell. Creep damage re-sults in progressive distortion of the vane sur-faces and the outer sidewalls. Excessive down-stream deflection may result in rubs with thefollowing rotor stage. Detection of excessivecreep and resulting deflection is assessed utiliz-ing three primary measurement techniques.Diameter measurements are taken on the innerand outer wall, diaphragm and labyrinth seals.Deviations indicate downstream deflectionand/or ovality. Nozzles are inserted into a fix-ture that simulates the turbine casing to checktheir fit-up in a turbine shell. Critical dimen-sions are taken to determine the amount of dis-tortion that nozzle has experienced and correc-tions are made. (See Figure 10.)



Figure 8. Metallurgical evalution of ADH repair onFSX-414

Figure 9. Applying ADH with syringe

Empirical deflection calculations are also madebased upon opening clearance data. Final veri-fication, performed by GE Installation andField Services (I&FS) field engineers, is simu-lated with deflection measurements carried outin the actual turbine cases of the hardware.These redundant checks define exactly howmuch upstream correction is required. Materialbuild-up and remachining yields a nozzle that iscorrectly repositioned between adjacent stagesof buckets. Specially-designed fixtures are usedto verify all dimensions prior to returning noz-zles to a customer.

The repair of newer technology stage two andthree nozzles made from GE’s patented GTD-222™ creep-resistant alloy includes refurbish-ing the airfoil with trailing edge coupons. Thesecoupons are specifically designed to addressphysical and metallurgical damage. Recent ad-vances have yielded an ADH repair for GTD-222™ nozzles. Additionally, select GE servicecenters now have Coordinate Measuring Ma-chine (CMM) capability to accomplish inspec-tion.

MS5001 second-stage nozzle refurbishment ofboth N-155 and FSX-414 metallurgy includesweld repair, restoration of diaphragm packing,heat pack modification and re-rounding thenozzle with machining or other techniques.MS3002 and MS5002 variable second-stage noz-zle refurbishment includes partition weld re-pair, shaft grinding and metallizing and hard-facing bushing areas.

Advanced Bucket RepairGas turbine buckets must operate in extreme at-mospheric and thermal environments whilemaintaining the structural integrity required ofrotating components. GE has determined all ofthe critical failure modes and has developed re-pair technologies and processes specific toeach. The failure modes most commonly en-countered for rotating hardware are listed inTable 4.

The first five modes are related to the turbine’soperating conditions and their subsequent ef-fects on bucket metallurgy. A single bucket istypically sacrificed from each set of buckets toundergo a destructive metallurgical evaluation.(See Appendix.) From that work, engineeringrecommendations are made on the bucket’scontinued serviceability. The reparabilityand/or weldability of the bucket and the re-quired repair methods and operations are alsodetermined.

Typical repair processes include blending, weld-ing, remachining and precision grinding. Theadvanced bucket metallurgy (vacuum cast nick-el-based superalloys) to support the higher fir-ing temperature gas turbines has requiredGlobal I&RS service centers to incorporate en-hanced repair processes as well.

1. Creep to crack initiation

2. Low cycle fatigue to crack initiation

3. High cycle fatigue

4. Corrosion/oxidation

5. Incipient melting

6. Interference with adjacent components

7. Excessive strain/distortion

8. Foreign object damage

9. Wear and fretting



1SEGMENT HOOK FIT

INNER DIAMETER

23

56

4

7

Figure 10. Nozzle diaphragm inspection

Table 4. Bucket failure modes

For repair of high strength bucket alloys likeGTD-111™, weld wire of the same compositionhas been typically used in the past. This assuresthat the repair exhibits strength and oxidationresistance similar to the parent material. A weldrepair process originally developed by GE’sAircraft Engine business has been adapted toindustrial gas turbine components and pro-duces crack-free high strength welds. The proc-ess, called WRAP™ (Weld Repair AdvancedProcess™), uses a controlled environment boxto regulate heat input and cover gas. In Figure11, a technician skillfully welds a bucket usingthe WRAP™ process.

For repair of high strength bucket alloys likeGTD-111™, weld wire of compatible composi-tion may be utilized based on the nature of therepair. GTD-111™ filler material may be usedwith an elevated temperature repair process orthe newly developed “Bktaloy” (Bucketalloy™)may be utilized for an ambient temperature res-toration. This assures that the repair exhibitsthe strength, oxidation resistance and serviceendurance similar to the parent material. (SeeFigure 12.)

An alternative to the high temperatureWRAP™ process effects the repair at ambienttemperature with the use of an adaptive robotand specially designed welding fixtures. The sys-tem has the objective of welding the squeelertips of turbine buckets of specific configurationautomatically. The unique shape and position-al variation of the bucket makes automation ofrepair processes difficult. The robot is a manip-ulative arm with six axes of motion. The auto-matic welding system is specially designed toadaptively change key parameters to weld eachbucket tip to full height based on the edgethickness and position of the airfoil contour.(See Figure 13.) The basic parts of this system arethe robot, the tooling, the welding system, theadaptive control system and the safety provi-sions. The robot is made up of very precise com-ponents including brakes, transmission systems,electric motors, and counterweight systems todeliver the process within the three-dimension-al area known as the working area. Within thisentire complex system are methods that will cal-ibrate and visually monitor the process of weld-ing the buckets.

The tooling is comprised primarily of a processfixture which places the bucket in a specific lo-cation within the operating range of the robotworking zone and the vision system camera.The fixture must also provide a heat sink to thepart being welded and be designed to functionvery close to the welding arc without damage



Figure 11. WRAP™ weld operation

BktaloyTM

Alloy 625

Figure 12. Oxidation characteristics of weld repair alloys

during the welding process. The welding systemgenerates heat into the part, the welding torchand the fixture which must be dissipated whilein operation. A water chiller is part of this sys-tem to perform the function of cooling thecomponents.

The process selected for welding the filler ma-terial to the bucket is the plasma arc weldingprocess. A key to the process is the stable lowcurrents which enables accurate weld place-ment and welding on thin knife edge surfaces.Key to the success of this welding process is thedistance that the welding torch maintains fromthe weldment. An arc length controller utilizesthe arc voltage and sensing devices to adaptive-ly adjust the torch height and maintain a con-stant arc length for successful welding results.(See Figure 14.)

Post-weld heat treatment, Hot Isostatic Press(HIP), finish machining and grinding are easilyaccomplished while returning the bucket to itsrepair part dimensional requirements. The ele-vated temperature WRAP™ welding is also usedfor the restoration of rubbed tips and angelwing sealing surfaces.

Additionally, the elevated temperature WRAP™process is used to generate cutter teeth on theintegral labyrinth seal surface of shroudedbuckets. This uprate is offered on new and serv-iced parts. The use of honeycomb material instage two and three shrouds requires that thestage two and three buckets have “cutter teeth”on the bucket tip seals. Their purpose is to allowthe buckets to cleanly cut into the honeycombmaterial when the rotor moves axially relative tothe shrouds.

Restoration of integral shroud “Z” interlocks isaccomplished via the fusion application of wear-resistant hard surfacing materials. In the case ofGTD-111, the elevated temperature WRAP™process is again employed. For “Z” interlocksoriginally employing plasma-sprayed chromecarbide, this original material can be reappliedor, at the customer’s option, upgraded to fu-sion-applied hard surfacing.

Bucket cooling effectiveness is a critical part ofensuring bucket life and integrity. Higher firedmachines employ conduction and convectioncooling as well as film cooling techniques to en-sure that bucket temperatures do not exceed



Figure 13. Automated weld repair system

Reduction of Hot Zones (RED) as predicted byDesign Engineering modeling with the applica-tion of Advanced Thermal Barrier Coatings.

Figure 15. TBC effect on airfoil bulk metal surface temperatures

Figure 14. Close-up plasma torch

design limits. GE’s I&RS Service Centers, dur-ing repair cycles, ensure that the cooling pas-sages are not constricted or blocked. Applyingan Advanced Thermal Barrier Coating to theexternal surfaces of the bucket airfoil can re-duce the bulk metal temperature of the bucket.(See Figure 15.) Contact GE Energy Services foradditional information about the correct coat-ing for your particular application.

RotorsDuring a common day, a base-loadedMS7001EA will ingest approximately 56 millionpounds of air. The chemical composition of theair entering the compressor inlet in terms of hu-midity, trace gases and particulate determinethe extent of corrosion, erosion and depositwhich the air flow path surfaces exhibit.Deposits on the surface of the gas path compo-nents are carefully removed for initial inspec-tions. The operating environment of the tur-bine rotor affects the maintenance needs andthe inspection phase of the rotor overhaulcycle.

The full workscope of complete overhaul of aGE rotor can only be performed once the ini-tial incoming inspection is accomplished.Once the compressor rotor is thoroughlycleaned, the assembly is visually inspected and

characteristics such as wear, corrosion, macro-cracking, nicks and dents are fully documented.(See Figure 16.) GE has established criteria towhich these inspection results are comparedand decisions are made as to the workscope re-quired to repair the assembly.

The functionality of the rotor is dependentupon the dynamic balance and vibration as-pects that the rotor as an assembly exhibits. Aspart of GE’s recommended rotor overhaulworkscope during a rotor inspection, the totalassembly is set up in a low-speed balance ma-chine. A low-speed balance check of the rotor ismade to determine any imbalance, its magni-tude and location. Runout data is obtained onmultiple diameters throughout the assembly toensure the rotor concentricity and straightness.Each service center located throughout theglobe has made the investments to provide sim-ilar capability in support of the growing fleet ofgas turbines and the high standards that GEmaintains.

In general, turbine rotors experience the samemechanisms of wear and degradation that com-pressor rotors face. Due to the extreme temper-atures in the turbine, high temperature corro-sion, creep and oxidation also contribute tocomponent distress.

Some instances require that turbine and com-pressor wheels be given a rejuvenation of rabbetdimensions. These instances involve specialprocessing such as High Velocity Oxy-Fuel(HVOF) sprayed deposits that have near-basematerial properties and can be precision ma-chined. Specialized measurement tooling andprocedures analyzed with Six Sigma method-ologies have been implemented globally. Theyhave demonstrated improvements to the assem-bly process and to the overall performance ofthe assembly long term.

At assembly, the GE gas turbine rotor construc-tion practice is to individually balance rotor



Figure 16. Compressor and turbine rotor assembled after cleaning

components, (e.g. stub shafts, blade and wheelassemblies, distance pieces, and turbine wheelsand spacers). These components are assembledinto major subassemblies using a computerstacking program to minimize any runouts ofthe assembly. GE has developed specializedtooling for FA class compressor rotor applica-tions to improve the rotor straightness and min-imize runout. (Seee Figure 17.)

GE recommends that each row of rotor bladesand buckets be moment weighed and chartedprior to installation to ensure the balance of therotor. GE service centers are equipped to per-form this type of work with highly accurate mo-ment weighing and charting equipment. (SeeFigure 18.) The moment weight measurements

are taken using a balance beam system to simu-late the distance of the bucket from the rota-tional axis. The unit is computerized to recordthe measurements and run a program to selectthe bucket order (charting) that minimizes im-balance for that set of hardware. Records arekept so that in some cases if a bucket is dam-aged in service and needs to be exchanged, itcan be done so with a bucket of similar weightwithout the need to re-weigh the entire set ofbuckets.

The major subassemblies, which consist of thecompressor and turbine rotor assemblies, arethen balanced in two balancing planes. With asingle-shaft, two-bearing unit, such as MS5001,MS6001, MS7001F, or MS9001F, the matedcompressor and turbine rotors are final-bal-anced by adding correction weights distributedin three or four planes according to axial rotormass distribution.

GE global service centers have the factory-spec-ified balance equipment and the skilled trainedtechnicians to meet the design criteria outlined.Service center engineering personnel arelinked to the GE Energy Services Product Serv-ice organization to support critical rotor issuesas they arise during outages or on-site inspec-tion processes. Further, in 1994, GE introducedtransportable low-speed balance systems capa-ble of performing the rotor inspection and bal-ance operations at the customer’s plant site.This has helped to reduce customer costs dra-matically and determine rotor characteristics atthe site very quickly.

Optimizing your rotor may involve upgradingwith advanced components during the outagecycle. This effort has been shown to enhancethe performance of your turbine dramatically.GE service centers are poised to help customersunderstand what it takes to get the most powerfrom the turbines in place or to contact our web



Figure 17. 7FA compressor with GE’s multi-bolt tensioning device

Figure 18. Bucket weighing and charting equipment

sites for existing information and programs.Figure 19 shows a Frame 7B rotor that has beenconverted to a Frame 7E configuration usingseveral new wheels and buckets.

Combustion HardwareIn general, there are two primary failure modesassociated with all combustion hardware. One iswear at the mating surfaces that connect thecombustion components to each other and tothe remainder of the turbine. The other isdegradation of the Thermal Barrier Coating(TBC) system.

TBCs and their application will be thoroughlyaddressed in another section of this paper.However, in order to more closely monitor thedegradation of the TBC system, global I&RSservice centers have recently introduced non-destructive thickness surveys for combustioncomponents as a part of their incoming inspec-tions. This process allows the I&RS service cen-ter process engineers to better assess the abilityof an existing coating to remain serviceable foranother inspection interval without replace-ment. This process is shown in Figure 20.

A recent addition to GE’s service offerings is re-furbishment of 6FA combustion components.Tooling fixtures and methods for the repair ofall 6FA combustion components have been de-veloped. 6FA combustion liners are very similar

to the 7 and 9FA DLN-2 designs. However, thetransition pieces are quite different because theunit only has six combustion cans.

Combustor A critical repair operation for louvered com-bustion liners is air-flow testing. Flow testing as-sures that each combustion liner in the set isflowing the same amount of air, thus minimiz-ing temperature variances. (See Figure 21.)

When a liner is tested, it is placed on the flowcheck machine and a vacuum is drawn throughthe liner. The test machine calculates the effec-tive air flow area. A determination is then madeas to whether corrections are necessary.

Repair procedures for all types of Dry Low NOx(DLN) components have been developed. OnDLN-1, procedures have been established forthe restoration of the liner body, venturi, andthe cap. They may include repair or replace-ment of fuel nozzle collars and other minorpiece parts.

DLN-2 liners require a repair operation that re-moves all body distortion by straightening androunding the liner wall, returning the compo-



Figure 19. Upgraded turbine rotorFigure 20. Non-destructive thickness survey for

TBC on transition pieces

nent to right cylinders. The process involvesmechanical adjustment of the liner bodies withappropriate heat treatment procedures. Cir-cumferential cracking around the aft end of theDLN-2 liner is also a common distress. Theseliners can be made more robust by the replace-ment of the aft section with a design that pro-vides better cooling. TIL 1240 covers this modi-fication in some detail.

DLN-2 cap assemblies are restored by bothpiece part replacement and/or repair, depend-ing on the severity and type of wear.Impingement plates on the cap often crack andrequire weld repairs. The many tiny coolingholes in the cap are restored by ElectrodeDischarge Machining (EDM) after the weld re-pairs.

Transition Pieces Most turbine-run transition pieces (TPs) expe-rience distortion around the picture frame dueto time and temperature causing excessive gapsbetween the end seal slots between adjoiningtransition pieces. Uniquely designed inspec-tion fixtures are employed to ensure the dimen-sional fits of the transition pieces against themating surfaces of the turbine. A single-piecefixture is used for individual adjustments and a360° fixture is used to fit-up a complete set, tosimulate installation in a unit. Coordinate

Measuring Machine (CMM) technology isbeing implemented in select service centers inorder to minimize inspection times and im-prove accuracy.

Where needed, oversized end seals are used toassure proper seal engagement. The custom fitseals are sized during the final inspection in the360° fixture which simulates installation in themachine. (See Figure 22.) This saves time andmachining costs during installation in the tur-bine. However, turbine shell and first-stage noz-zle “out-of-roundness” may alter the simulationfixture data obtained by the service center.

When it is more expedient to replace the pic-ture frame, another fixture is employed. Re-placement picture frames are aligned in the fix-ture and welded in place. The replacementframes can be manufactured from original ma-terial, or in some instances a more creep- orwear-resistant material may be employed,depending on the nature of the distressencountered.

In FA model TPs, cracking is also commonalong the body sidewall. This cracking can bevery severe, and requires repair using couponinserts to replace damaged areas of the TP bodywith new material. GE has also developed amodification to the TP outer impingementsleeve that can be retrofitted to existing transi-



Figure 21. Combustion liner air flow test machine

Figure 22. 360° transition piece fixture

tion pieces. This modification will direct morecooling air to the body sidewall area, to mini-mize the cracking. The modification is shownbelow in Figure 23.

Fuel NozzlesThe global service center network repairs alltypes of GE fuel nozzles, from single tip “gasonly” to multi-port dual fuel DLN-2 units. Theevolution of combustion systems from single-tipto multi-tip fuel nozzle systems has necessitatednew repair processes to be implemented at theservice centers. These repairs result in restoredfuel nozzles meeting new part dimensions andflow differentials that meet or exceed new partspecifications. GE’s service centers maintain abroad inventory of consumable parts, such asc-seals, gaskets and lock plates, for all fuel noz-zle types. This ensures the fastest turnaroundtime possible.

Flow testing of fuel nozzle tips and passagewaysis of critical importance, especially for multi-nozzle systems. It is vital that the same amountof fuel flows through each nozzle in a set.

Equalized fuel flow minimizes temperaturespreads as measured by the exhaust thermocou-ples and can-to-can pressure differences be-tween the combustors. Computerized flow-testequipment is used to meter and measure flows.Air-flow testing (Figure 24) is used for gas and airpassages and water-flow testing is used for liquidpassages.

The flow-test units use a computer-controlledsystem that calculates the percent variation ofeach to that of the set tips. Bodies or covers aretested and then matched to fuel tips to com-pletely optimize the system. The final assemblyis typically limited to a variance of less than 2%between assemblies. All accumulated fuel-flowdata is saved for permanent records.



Figure 23. TP impingement sleeve “scoop” Figure 24. Fuel nozzle air flow test machine

Often, GE can help the customer trouble-shootany problems by doing an incoming flow test.Chemical analysis, performed by taking residuesamples as the fuel nozzles are disassembled,further identifies any additional fuel relatedproblems. After disassembly, the parts arecleaned using ultrasonic equipment or glassbead blast. Parts then go through a non-destructive testing (NDT) process where bodiesand covers are pressure checked for leaks.Detailed reports of fuel nozzle performance arethen generated for the customer’s review.

Component Enhancement

Extendor™ GE has established a protective package, theExtendor Wear Kit, that addresses the mostcommon areas of wear on liners, transitionpieces and fuel nozzles (See GEA 12276). Kitsare available for Frame 6B, 7E/EA and 9E com-bustion systems, whose units typically run inbaseload applications. Wear points throughoutthe combustion system are modified, includingtransition piece “H” blocks and bullhorn brack-ets, floating and end seal slots, and liner inter-face. The liner modifications include the fuelnozzle and crossfire collars, liner stops andspring seal. Flow sleeves, fuel nozzles and somecrossfire tubes are also modified. The major GEservice centers have been qualified to make allof the wear enhancing modifications to thecombustion components. Special fixtures areused to position the modification and replace-ment parts for optimal fit in the turbine.

Coatings

Compressor Corrosion Protection Protective coatings used on heavy-duty gas tur-bine compressors are divided into two classes:barrier coatings and sacrificial coatings. Barriercoatings isolate the corrosive environment fromthe steel substrate, while the sacrificial coatingsprovide a reservoir of reactive metal in a gal-vanic couple. To avoid potential failure scenar-ios from single layer coatings, GE’s preferredrepair for corrosion protection utilizes both anon-conductive barrier coating over a sacrificialcoating. The barrier coating prevents the sacri-ficial coating from continually reacting with theenvironment, while the sacrificial coating pro-tects the base metal from attack in the event ofbarrier coating breach. If a breach occurs, thebarrier coating limits the corrosion cell to thebreach area.

The dual layer coating consists of a sprayed-onaluminum-based layer that is burnished tomake it conductive, followed by a ceramic-basedtop layer that forms the barrier. (See Figure 25.)These coatings have been applied to individualblades and wheels or to fully bladed and stackedrotors.

Turbine Corrosion/Oxidation If a turbine bucket’s external coating isbreached or compromised, the bucket requiresa repair coating to protect the nickel-base alloyfrom oxidation and corrosion attack. The met-allurgical evaluation discussed previously deter-mines the extent of distress and whether thebucket is repairable. A chemical stripping proc-ess is employed to remove all of the servicedcoatings on repairable buckets.

Any welding, dimensional restoration and sub-sequent processing is performed on buckets inthis stripped condition. GE reapplies its pat-ented Extendcoat GT-29™ or Extendcoat GT-33™ chemistries using a proprietary thermalspray process. These coatings provide a surfacereservoir of elements that form protective andadherent oxide layers, thus protecting the un-derlying base metal from oxidation and corro-sion attack and degradation. The primary coat-ing applications are listed in Table 5. By virtue ofits higher aluminum and nickel contents rela-



Figure 25. Compressor airfoil coated with GECC-1

tive to GT-29™, GT-33™ offers a significant im-provement in high temperature oxidation re-sistance and improved ductility and crack prop-agation resistance. On the other hand, a reduc-tion in chromium content results in some lossof hot corrosion resistance relative to GT-29™.Type II low temperature corrosion and Type Ihigh temperature corrosion may occur when al-kali metal salts condense on a part surface anddestroy the normally protective oxide scale.Low temperature corrosion is only a concernwhere temperatures are below 1350°–1400°F,but it has a high rate of attack. Type 1 corrosionwould only be a concern in the temperaturerange 1400°–1700°F where contaminants arepresent. Chromide pack coatings are effectivebarriers to Type II corrosion.

Coating Composition Oxidation Type I Type IIType Resistance Corrosion Corrosion

Resistance ResistanceGT-29 CoCrAlY Poor Excellent PoorGT-33 CoNiCrAlY Good Good Poor

GT-29IN- CoCrAlY + Very good Execellent PoorPLUS internal and

externalaluminide

Chromide Cr Poor Good Very goodCoating

Either of these repair coating systems can be ap-plied with the addition of an over-aluminide.The combination of Extendcoat with over-alu-minide is identified with a PLUS™ designation.Buckets with internal air cooling may requirethe over-aluminide be reapplied to the internalpassages as well. The designation for bucketswith internal and external aluminide coatings isIN-PLUS™. The aluminide is provided to en-hance oxidation resistance.

Thermal Barrier Coatings Thermal barrier coatings (TBCs) are reappliedto combustion components to provide an insu-lating layer that reduces the underlying base

material temperature and mitigates the effectsof hot streaking or uneven gas temperature dis-tributions. TBC characteristics and advantagesof TBCs are listed in Table 6.

Characteristics• 15-25 mil Thickness• Insulating-porous• Plasma sprayed in air• Two layers

bond coat - NiCrAlYtop coat - Yttria-stabilized Zirconia

Advantages• Reduces metal temperature of cooled compo-

nents• 8-16°F Reduction per mil of coating

GE emphasizes the importance of applyingTBC robotically to ensure quality and repeat-ability not available with manually applied coat-ings. An operator, encumbered with the re-quired protective gear, cannot come close tothe accuracy and repeatability in terms of plas-ma gun distance and traverse speed to that ofrobotically applied coatings. Figures 26 through28 display robotic coating operations per-formed at one of GE’s service centers.

GE’s service center network has standardized itscoating equipment and robotic capability with



Table 6. TBC coating

Table 5. Coating applications

Figure 26. Robotic application of TBC on MS7001Etransition piece

that of GE’s gas turbine manufacturing opera-tion (GE Gas Turbine, LLC), which applies TBCto new OEM components. This standardizationallows the use of the same qualified programsthroughout the service center network, ensur-ing quality product every time. The significancein using OEM generated programs is that allhardware must be restored to OEM di-mensionsor else the robotic arm would crash into the out-of-tolerance component. It also minimizes theglobal inventory of spare parts needed for thethermal spray equipment.

TBCs are divided into classes depending on thebond coat and top coat thickness. Class B TBCs(0.014"/0.3556 mm to +/-0.004"/0.1016 mmtop coat) are the standard for pre-DLN series

combustion liners. (See Figure 29.) Class C coat-ings (0.020"/0.508 mm to +/- 0.002"/0.0508 mmtop coat) significantly improve the cooling ef-fect on selected DLN liners.

Transition pieces may receive either coating(Class B or Class C). However, the differencesbetween robotically-applied and manually-ap-plied coatings are more pronounced on thesecomponents. The nature of the hot gas im-pingement on the transition piece wall causegreater thermal distortion than what typicallyoccurs in combustion liners (e.g. axial flow).

Thickness uniformity is critical to transitionpiece coatings reaching their expected life. Ifthickness variations occur during manual sprayapplications, then chances are high that thecoating will spall during thermal cycling. This isshown in Figure 30 and Figure 31 by two transi-tion pieces run in a rainbow test. Figure 30 dis-plays a transition piece with robotically-appliedcoating. The TBC coating is still intact after8,000 hours. Figure 31 illustrates a transitionpiece from the same unit, with a manually-applied coating. This transition piece hasspalled coat-ing under the hanger bracket.

TBCs on nozzles have been proven to extendthe life of nozzle segments, and are also offeredas a repair or upgrade modification to stage 1nozzles. Figure 32 shows TBC applied to nozzle



Figure 27. Robotic application of TBC on MS7001Etransition piece

Figure 29. Photomicrograph of Class B TBC

Figure 28. Robotic application of TBC on MS6001Bcombustion liner

partitions, while Figure 33 shows TBC applied toa nozzle sidewall and leading edge.

Recent advances in nozzle coating technologyinclude a Class A TBC (MCrAlY bondcoat withan yttria-stabilized topcoat). Maintaining thecritical dimensions of the throat area during thecoating application is accomplished by con-trolled robotic application. This assures that thenozzle’s airflow and harmonics are not com-promised, as can happen with manually appliedcoatings. Special finishing operations also as-sure proper gas flow dynamics. When these ma-terial enhancements are combined with GE’srobotic control process, a superior life exten-sion product results.

Service BackgroundGE has developed an entire technology area forits gas turbine repair businesses. By coordinat-ing the repair business (Global Inspection andRepair Services) with GE Gas Turbine, LLC, GEPower Systems has reduced repair technologydevelopment and implementation cycle timesto the marketplace.

GE’s gas turbine repair business is a global net-work of wholly-owned and joint venture facili-ties. Figure 34 shows the facilities’ global loca-tions. Including service centers that work onlyon steam turbines and generators, there aremore than 50 repair facilities around the world



Figure 30. Turbine run transition piece with roboti-cally-applied TBC (8,000 hours)

Figure 31. Turbine run transition piece with manu-ally-applied TBC (8,000 hours)

Figure 32. TBC applied to nozzle partition

Figure 33. TBC applied to nozzle sidewall

and leading edge

for the repair of GE-designed power generationequipment. To enhance the sharing of bestpractices among repair facilities, componentteams have been formed for buckets, nozzles,rotors, combustion hardware, fuel nozzles, andcoatings. These teams have members from eachrepair facility, as well as representatives fromEnergy Services and Power GenerationTechnology and commercial support organiza-tions. The teams communicate on a regularbasis to share information and work togetheron improvements in global repair procedures.

The global network of service centers is sup-ported by Gas Turbine Design Engineering,Manufacturing Engineering, Reliability Engi-neering, Materials and Processes Engineering,New Products and Processes, as well as GE’sCorporate Research and Development Center.In addition to the support given by the above-mentioned organizations, the repair facilitiesare partnering with The Repair DevelopmentCenter at the GE Aircraft Engines facility inCincinnati, Ohio. The repair philosophy is sim-ple: “restore all components to OEM specifica-tions.”

In order to better serve the customer and un-derstand metallurgically intense processes, GE’sInspection and Repair Services business is in-vesting to have fully operational metallurgicallabs in the U.S., Europe, and Asia. These facili-ties will be used to support repair processesfrom a materials and serviceability viewpoint, aswell as to provide the customers with informa-tion about the condition of their componentsprior to commencement of repair. (See Appen-dix).

The technology and processes generated inmeeting this objective are shared with andtransferred to GE repair facilities worldwide.Periodic audits and component team meetingsensure the sharing of best practices throughoutthe Global Service Center Network.

GE’s Global I&RS also maintains a training cen-ter in Schenectady, NY for repair engineers,craftsmen and technicians. Employees from allgas turbine service centers gather to learn thelatest repair techniques, as well as to share andexchange information. Students spend approxi-mately 30% in the classroom and 70% on the



28

Global Service Center Network

23 - PG15 - Non-PG

ALGESCOTGTS

GEPSIL

GENTS

GE MEELSA

W&A

Turbimeca

Ponce

Basildon

Aberdeen

FierroCIMISA

1 - PG6 - Non-PG

• Maximize Current GT Facility Space & Capacity -Work shifts 7 X 24 - Use non-GT Space

• Leverage Global Network of GT Centers - Share People/Best Practices - Component Teams

• Continue to Add Capacity - Add FCapability to non-F GT Centers/New J V

PGT

CincinnatiHouston

GEESE (Bourogne)

Figure 34. Global gas turbine service centers (www.gepower.com)

shop floor perfecting the proper techniques.Courses cover the turbomachinery as well asfuel nozzle repair of the entire GE product linecurrently in service. Courses are added as newrepairs are developed and new product linesare released into service. The ultimate goal ofthe training center is for GE gas turbines to bere-paired utilizing the best techniques andproce-dures, regardless of geographic location.

SummaryThis paper describes some of the repairprocesses and technologies currently used by

GE’s Global Inspection and Repair Services op-eration. It also serves to verify GE’s commit-ment to customer service and continued leader-ship in the development and implementationof “state-of-the-art” gas turbine repairs. The ac-tivities described in this paper are by no meanscomplete. Major initiatives are continuouslybeing initiated to assure that GE maintains itsmarket leadership.



Appendix

Destructive Analysis: A Tool forUnderstanding Component Life

GE Meeting Industry’s Demands The GE network of metallurgy laboratorieshave a wide range of capabilities to deal withthe many material issues faced during the re-pair of Hot Gas Path components. (See Figure35 and Figure 36.)

The services that these laboratories providehave been developed to meet the exactingneeds of the Power Generation and Oil & Gasindustries. Each analysis is conducted to a con-sistently high standard by a dedicated team ofexperienced technicians and is supported byGE Materials Engineers.

Material Issues Gas turbine buckets are exposed to severeloading conditions, both in terms of tempera-ture gradients and stress concentration. Anymechanism that influences the material mi-crostructure likely varies bucket behavior andmay adversely affect component life. It is there-fore essential that the bucket coating/ basematerial system is characterized to assess thecomponent set integrity.

Limitations of Non-Destructive Evaluation Non-Destructive Evaluation (NDE) can provideinformation on the effect of service on compo-nent integrity. However, many life-limiting ma-terial characteristics cannot be assessed by suchtechniques. (See Figure 37.)

Destructive analysis is often the only reliableand accurate means to obtain details from crit-ical features beneath the surface that restrictcomponent performance. Destructive investi-gations therefore play a central role in assess-ing the component set integrity. (See Figure 38.)

The Need for Destructive Analysis Destructive analyses obtain fundamental infor-mation to help determine the necessary repairworkscope. Selecting the appropriate rejuvena-tion program optimizes component life exten-sion and gas turbine efficiency. Furthermore,



Figure 35. Houston Service Center

Figure 36. Basildon Service Center

Figure 37. Infrared thickness measurement

the information gathered during a destructiveanalysis can be studied together with the gasturbine running conditions to help identify thecritical operating parameters. The customer isthereby able to understand component behav-ior so that future operating conditions can beoptimized for enhanced machine perform-ance. (See Figures 39–42.)

Benefits of Destructive Analysis • Establishes possible sources of contamina-

tion from chemical characterization of cor-rosion products.

• Determines the most effective repairworkscope by characterizing the internalcooling hole microstructure, which often dif-fers from the behavior of the external mate-rial.

• Correlates component service temperaturefrom both gamma prime coarsening and dif-fusion zone growth.

• Prevents blending of sound base material byestablishing crack location, frequency andpenetration.

• Minimizes cost associated with non-valueadded work by identifying irreparable com-ponents early in the rejuvenation program.

• Helps determine the risk of component fall-out prior to blending. Ordering the appro-priate components early maximizes availabil-ity of replacement OEM parts for re-installa-tion into the gas turbine.



Figure 38. 9FA bucket section by EDM

Figure 39. Serviced 9E bucket

Figure 40. Microscopic examination

Figure 41. Characterizing bucket features

Customer Satisfaction Considering the value of destructive analysis, itis not surprising to learn the high level of satis-faction from customers who have requestedthis type of investigation.

Destructive analysis will play a critical role infuture repair schemes and the facilities at theGE Service Centers will seamlessly evolve sothat destructive analysis continues to satisfycustomer expectations.

Find out more To discuss your specific requirements in moredetail or to receive additional information,please contact your nearest GE Service Center.You can find us online at www.gepower.com.



Figure 42. Determining crack penetration

List of FiguresFigure 1. Stress cracked bucket

Figure 2. Trailing edge specimen

Figure 3. Metallurgical evaluation showing chrome depletion/oxidation

Figure 4. Nozzaloy™ repair over ADH

Figure 5. Nozzaloy™ crack initiation

Figure 6. Nozzaloy™ thermal fatigue characteristics

Figure 7. Nozzle requiring ADH repair

Figure 8. Metallurgical evaluation of ADH repair on FSX-414 nozzle

Figure 9. Applying ADH with syringe

Figure 10. Nozzle diaphragm inspection

Figure 11. WRAP™ weld operation

Figure 12. Oxidation characteristics of weld repair alloys

Figure 13. Automated weld repair system

Figure 14. Close-up: plasma torch

Figure 15. TBC Effect on airfoil bulk metal surface temperatures

Figure 16. Compressor and turbine rotor assembly after clean

Figure 17. Compressor with GE’s multi-bolt tensioning device

Figure 18. Bucket weighing and charting equipment

Figure 19. Upgraded turbine rotor

Figure 20. Non-destructive thickness survey for TBC on transition pieces

Figure 21. Combustion liner air flow test machine

Figure 22. 360° transition piece fixture

Figure 23. TP impingement sleeve “scoop”

Figure 24. Fuel nozzle air flow test machine

Figure 25. Compressor airfoil coated with GECC-1

Figure 26. Robotic application of TBC on MS7001E transition piece

Figure 27. Robotic application of TBC on MS7001E transition piece

Figure 28. Robotic application of TBC on MS6001B combustion liner

Figure 29. Photomicrograph of Class B TBC

Figure 30. Turbine-run transition piece with robotically applied TBC (8,000 hours)

Figure 31. Turbine-run transition piece with manually applied TBC (8,000 hours)

Figure 32. Nozzle TBC

Figure 33. Nozzle TBC

Figure 34. Global gas turbine service centers



Figure 35. Houston service center

Figure 36. Basildon service center

Figure 37. Infrared thickness measurement

Figure 38. 9FA bucket section by EDM

Figure 39. Serviced 9E bucket

Figure 40. Microscopic examination

Figure 41. Characterizing bucket features

Figure 42. Determining crack penetration

List of TablesTable 1. Major life limiting factors

Table 2. Potential failures modes - hot gas path components

Table 3. Turbine Component Life Flowchart

Table 4. Bucket failure modes

Table 5. Coating applications

Table 6. TBC coatings



Gas Turbine Technology

Documents

Transcript of Gas Turbine Technology