Gas Turbine Component Repairs:Why Value Matters

Frame 6B Users Group, Jacksonville FL 2007Doug Nagy, P.Eng

dnagy@liburdi.comManager, Turbine Component Repairs

Liburdi Turbine Services Inc

Presentation Outline

• “Quality”, “Cost” for component repairs• The added cost of missing quality• “Value” – Looking after the total life cycle costs• Examples of high Value repair services and

upgrades• Selecting a Value repair partner

Quality and Cost for Repair Services

“Quality” = Meets all requirementsThe term “high” quality is commonly used but –the service is either “quality” and meets all requirements, or it is not “quality” and does not meet all requirements

“Cost” = The price you pay for the repair serviceCosts can be lowered by choosing the lowest bid price,

but it is more valuable to lower your total maintenance costs over the life of your asset

Quality Component Repair

• Meets all requirements for– technical specifications – materials used, processes

used (and not used), repair limits,– dimensional requirements, – future serviceability, – cost,– reliability, – delivery

• Resulting repair will be reliable with minimum risk of service problems – will behave similar to original new part during the next service interval

Poor Quality - ExamplesRepair does not meet Requirements

• Welded in inappropriate areas (repair limits exceeded)• Welded with inferior weld alloy (strength, hardness)• Welded with inferior weld alloy (oxidation/corrosion)• Coating inappropriate (oxidation/corrosion)• Coating out of specification (thickness, composition)• Critical dimensions not fully restored• All defects not identified and corrected• etc

Poor Quality - ExamplesRepair does not meet Requirements

Poor Quality Why does it happen?

• Unregulated industry (compared to flight engines) -- different standards practiced by each vendor

• Expedience (shortcuts) to save cost or time• General lack of knowledge or experience - specs, design

considerations (vendor does not know the difference)• Lack of Engineering oversight and experience• Disregard for QA system, or lack of QA system• Lack of capability – unable to weld alloy, etc• Lacking best available technologies

Component repair? Buyer Beware!!

Poor Quality - ResultsSignificant Increase in Life Cycle Costs

• Repair is not Reliable in service• Repair leads to:

– Early removal ($cost), – In-service failure ($$$cost)

• Parts not repairable at end of service interval: – $$cost of early replacement parts

• Low yield of repaired parts: – high $$cost of replacement parts to complete set

The price paid for the repair is a small part of the total life cycle value and cost for the component set

“Value”

The alternative is to consider “value” in component repair decisions

“Value” = Quality repair service: One that provides positive cost-benefit over a period of time (life cycle)

“Value” Repairs - Life Cycle Cost Savings

• High Yield of repaired parts – minimize need for expensive new replacement parts

• Ensure future reparability buy allowing multiple service intervals for the parts

• Reduce risks, re-establish design safety margins• Superior to conventional repairs, AND in some cases

superior to original new part. “Upgrades” are repairs that address the weaknesses of the original design

Upgrades are based on lab analysis of service-run parts, -- info the original designer did not have

“Value” Repairs – Examples

• Shrouded Blade Weld Repair Upgrade –– Life Extension and Upgrade

• Bucket Tip Weld Repair and Upgrade– Life Extension and Upgrade

• Stage 1 Bucket Rejuvenation and Internal Coating –– Life Extension

• Nozzle – High Strength LPM Repair– Life Extension and Upgrade

• Stage 2 and 3 Bucket Repair and Upgrade– Upgrade and Life Extension

RB211 24C HPT Blade Weld RepairValue = Full Service Intervals and Extended Life

13,000 hours since

conventional weld repair of shroud edges

24,000 hours since

Value weld repair and Upgrade

Cost savings to large fleet operator – over $30 Million over 10 years

“F” Class Blades - Value RepairWelds with Superior Oxidation Resistance

7FA Stage 1 Bucket

• Severe oxidation attack and metal loss at blade tip

• Oxidation resistant weld alloy applied to repair tips

• Weld alloy has superior oxidation resistance to the original blade alloy.

• Frame 7EA Buckets, rejuvenated three times, have reached twice the usual service life

• Running out to 100,000 – 120,000 hours

Buckets at 92,000 hoursReady for repair and

further service

Frame 7EA Stage 1 BucketsValue = Extended service life cycle

Cost savings to 4 engine fleet – over $5 Million over 6 years

• Repair may be heat-treated with a “partial solution”. Only a fraction of the alloy creep strength is restored. This has proven to have no significant benefit*

• A “full-solution” heat-treatment with HIP fully rejuvenates alloy creep strength. These proprietary processes are not mere repeats of OEM heat-treat cycles.

t

T

Gamma PrimeSolvus

Partial Solution Cycle

Full Solution Cycle

Rejuvenation Heat treatments vsPartial Solution Heat treatments

* Mike Woods ERA Technology: Turbine Forum, Nice, April 17-19, 2007

time

tem

pera

ture

• In the case of aged material, partial solution cycles are ineffective• Aged Gamma Prime phase must be fully restored to rejuvenate alloy

ServiceExposed

Full Solution Heat Treatment

DS GTD111 alloy

Stage 1 bucket

Rejuvenation Heat treatments vsPartial Solution Heat treatments

Stage 1 Buckets - Restore ALL Coatings Internal Aluminide and External MCrAlY

• Conventional repair has limited life cycle – internal coatings are not restored

• Value repair - the internal coatings are chemically stripped and replaced

• Removal of ALL coatings is necessary to perform FULL rejuvenation heat treatments

• New coatings, internal and external applied every 24,000 hours – parts are protected through full life cycle

Nozzles:Value = Extended service life cycle

• 48,000 hours during advanced repair• Areas with large cracks repaired with

high-strength LPM material• Even thinned airfoils can be restored

with sheets of LPM material

Value: Cost savings during repairs and continued service intervals

• 92,000 hours second repair• Areas with repaired cracks show less

re-cracking, sometimes none• LPM material can be re-repaired

LPM: Weldability

• LPM can be welded by GTAW (TIG) methods

• As with any superalloy, good control of heat-input and constraint are required.

Stage 2 and 3 Buckets:Shroud Lift correction and coating

• Shrouds on buckets run hot and “lift”• Leads to early retirement or risk of failure• Coating on airfoil avoids casting metal loss

Value: Reliable continued operation, avoided replacement costs

Repairs that Create “Value”

“Value” = Quality service that provides positive cost-benefit over a period of time ( eg the life cycle)

• Life Extension – parts operated for additional service Intervals , in some cases doubling life.

• High Repair Yield – 100% of parts repaired – minimal need for new replacement parts to complete set

• Cost Savings - by prolonging the time until new part purchase is required, maximizing value from existing parts

• Better Technology enables upgrades that make parts better than new.

Cost savings of Value repairs over the component life cycle far exceeds the cost differences between conventional and Value repairs

• Primitive purchasing strategies include “five-bids” and a “buy”. These do not deliver the best supplier in terms of Value

• The Value suppliers have a long term outlook; – They look beyond the present repair to the total life-cycle cost for

your turbine components– They have a proven track record of extending component lives

based on advanced technology– They re-invest in the business by introducing new technologies. – They have comprehensive engineering and quality control plans

to support their work.

Selecting a Value Supplier

Working with a Value Supplier

• Prepare a purchasing document, but treat it as a guideline. Expect Value Suppliers offer their own recommendations.

• Value Suppliers will offer modifications and upgrades intended to reduce future damage and extend component lives.

• They understand the design constraints and therefore understand repair limitations. Don’t make the assumption that OEMs are also the experts on repair.

• Keep the dialogue open with some reasonable level of oversight. Participate in the repair process.

Summary

• “Quality”, “Cost” and “Value” for repairs– Defined for GT component management

• Value – examples of high Value repair services– Extended Life – 2 times conventional repairs

• Value – examples of component Upgrades– Superior coatings, oxidation resistant,weld alloys,

high strength repair materials• Selecting a Value repair partner

– Reputation and past experience is key factor

Thank-you for your time and attention