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Comments on the Avon "200" upgrade package.http://www.gas-turbines.ca/viewtopic.php?f=25&t=121

Comments on the Avon "200" upgrade package.byj79guy

I was asked to comment on the Avon "200" upgrade package that Rolls has available forthis product line. Here goes, I don't suppose I'll be getting a Christmas card.

Economic Alternatives to the Rolls Royce Avon 200 Modification Program

Background

Rolls Royce has recently announced what they describe as a significant upgrade to theIndustrial Avon gas turbine product line, promising; 1) Improved output. 2) Improved fuelefficiency. 3) Reduced exhaust emissions. 4) Improved overhaul life. 5) Reduced overhaulcosts.The following is an examination of these claims, based upon field and overhaul experiencewith the Industrial Avon product line, as a fully independent heavy maintenance andoverhaul depot, without any affiliation to Rolls Royce, and an offer of economicalalternatives:

An overview of the 200 modification revisions:- DS cast Hp. Turbine Blades. (Hpt Blades.)

- Hpt Blade tip sealing, and Tip Shrouds.- Hp. Turbine Disk and Blade root interface.- Metallurgy, Ip and Lp Turbine Blades.- Turbine Nozzle Guide Vanes. (Turbine Nozzles.)- Combustion Liners and Fuel Injection Nozzles. (Swirler Burners.)

Let us now discuss each of the modification revisions as per above.

- DS cast Hp. Turbine Blades.Improved, or really, increased output, for any gas turbine engine is strictly a function of

increased airflow, (Mass flow.) or increased firing temperature. (Expansion ratio.)As Rolls Royce is not proposing an increase in mass flow, then they are proposing toincrease the output via increased firing temperature only.To do this, Rolls has changed the turbine blade materials to allow an increase in firingtemperature. The root of this change is in the Hp Turbine Blades, which have beenchanged to single crystal cast. (As opposed to equiax cast in the regular Avon engines.)Rolls Royce commercial RB211 aero engine experience has demonstrated the ability of SCcast blades to better resist creep growth than equiax cast blades, when comparing, similarcooling regimens of like blades, and the only difference is the casting technique. Rolls,with the 200 modification has eliminated the cooling air used to keep Hpt bladetemperatures under control, and has elected to use solid blades, similar to the Mk-1533Hpt blades. Thus, when at full power, or increased power as proposed by Rolls, the Hptblades will in fact be operating at significantly higher temperatures than in Mk-1535engines.It must be clearly understood, that in order to achieve this increased output, that the

Posted: Tue Mar 03, 2009 9:00 pm
http://www.gas-turbines.ca/viewtopic.php?f=25&t=121http://www.gas-turbines.ca/viewtopic.php?f=25&t=121http://www.gas-turbines.ca/


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Reduced turbine blade tip leakage is undeniably an objective in maximising hot gas pathenergy, and transforming it into useable work. On paper, the revisions made by Rolls inthe 200 modification appear to be a step in the right direction, however one must takeinto consideration as a whole, the operating of industrial Avon units, and the effectivenessof such modifications in light of long term operations. Avon units, in their standardconfiguration have shrouded blade tips, which is the single most significant step towardsimproved turbine cycle efficiency, as compared to traditional General Electric type blades,which do not have such turbine blade tip shrouds. GE, in an effort to minimise hot gaspath losses, elect to run their turbine tip clearances extremely tight, and use abradeabletip shrouds to allow the blades to actually touch the stationary seals. It is common practiseto have to break in a freshly overhauled GE engine, as the turbine blades run on the tipshrouds quite hard, and upon first shutdown, may indeed lock the turbine rotor fromturning for several hours.Avon units, on test cell operation, have as part of their acceptance tests, a timed coastdown from the cut of fuel to the engine, from idle speeds. If the engine fails to meet aminimum run down time, the engine cannot be released to the customer. This is exactlythe opposite to General Electric philosophy, where tighter, is better, and their enginesare expected to stop very quickly on test cell shutdown.

In order to meet this minimum run down time, Rolls elects to assembly the Avon units withgenerous turbine blade tip clearance, which limits the ultimate effectiveness of such.Therefore, no matter what revised system Rolls elects to incorporate into the Avonproduct, without changing the break-in procedure on the test cell, or altering theminimum run down time, there is a distinct limit to the effectiveness ofrevised tip shrouds.

AlternativesInstead of electing the pay the premium price of the 200 modification, which includesrevised turbine blade tip shrouds and stationary seals, it is more economical to incorporate

stationary tip shrouds that have an abradeable surface (Typically an unfilled honeycombtype sealing surface.), together with extended turbine blade tip fences, which can beadded to standard blades during overhaul. During test cell running, the unit is run insequentially, to gently wear the turbine components in to each other, minimising hot gaspath blade tip leakage. Such is significantly more effective than the 200 modification,and is completely refurbishable at major overhaul intervals, at considerably less expensethan what Rolls presents to their customers.

- Hp. Turbine Disk and Blade root interface.With the Avon 200 modification program, Rolls has revised the Hpt blade root profile,and the mating Hpt disk assembly, which holds said blades.In the past, Rolls has experienced failure of the Hpt disk and/or Hpt blades at the fir-treeroot interface, and thus has elected to revise the fir tree root profile on the promise ofbetter fatigue resistance.

Advantages/DisadvantagesOn the surface, revision of the Hp turbine root profile appears to be a good modification,however one needs to examine the past modes that led to the failure of the Hp turbinecomponents; It has been demonstrated that the failure of these components was in nearlyevery case, caused simply by uneven combustor (Flame tube) loading. This uneven loading

in turn, was caused by uneven fuel flows into the combustors, or a disruption of thecombustion process in each combustor. Revision of the Hp turbine components, althoughmay lead to a reduced incidence of failure, however this is treating the symptom, not thecause. As with all Roll Royce turbine products that have separate combustor cans, (Can-annular combustion.) it is imperative that the fuel flows into each combustor must be


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balanced and even. By flow matching the fuel injection system components andmaintaining this system integrity, the incidence of Hpt turbine component failure iseliminated. (Those failures associated with uneven combustor loading.)By incorporating the 200 modification, the customer is cutting themselves off from thetraditional supply of commonly available standard turbine components and committing tounique turbine components that have yet to prove their ultimate effectiveness andlongevity. Pricing of these new type turbine components have already been demonstratedas being extremely high.

AlternativesThis fuel system flow matching can be done during engine overhaul at very low cost to thecustomer, and over the overhaul life of the engine, periodically checked during routineborescope inspection to keep the negative effects to a minimum. A spare set of flowmatched fuel injection nozzles, (Burners.) can be rotated into the unit during routineinspection. The removed fuel nozzles are then sent to depot for cleaning, and flowbalancing, which ensures the customer always has the lowest possible combustor loading,and subsequently reduced turbine system component stress. The original type Hp turbinecomponents are retained, and reliably operate over the life of the unit, without incurring

the expense of perhaps needlessly replacing such, with the goal of fixing a problemwhich may not exist.

- Metallurgy, Ip and Lp Turbine BladesWith the Avon 200 modification program, Rolls Royce has altered the base alloy of the Ipand Lp turbine blade materials. The claim is improved component longevity and overhaulcosts.

Advantages/Disadvantages

Upgrading the base alloys of the Ip and Lp turbine blades, is potentially a good idea, asalloys have advanced considerably in the last 15 years, giving better thermal creep growthlife, and resistance to hot gas path corrosion effects. However, the Rolls Royce IndustrialAvon units typically do not have a problem with the Ip and Lp turbine blades. The coatingsspecified for standard Avon units is a very mature specification, dating back to the early1960s. Currently there are a great many coatings available that offer vastly superiorperformance to the standard OEM coating, at economical pricing. It is most unfortunatethat the Avon 200 specification Ip and Lp. Turbine blades cannot be slowly incorporatedinto the Avon product line during overhauls as required, rather than a single, expensive,mass change out.

AlternativesThe application of modern corrosion and thermal resistant coatings to the standard Ipand Lp turbine blades, offers as much, or better of a component longevity advantage asthe expensive 200 specification blades. Should the customer require increased engineoutput, then the application of ceramic thermal barrier coatings to these blades offersmuch more to the end customer in terms of reduced overhaul costs.

- Turbine Nozzle Guide Vanes.Minor revisions to the turbine nozzles to allow a reduction in cooling air flow, and increase

vane segment rigidity.

Advantages/DisadvantagesAny reduction in cooling air flow to the turbine nozzles will result in an increase in turbinecycle efficiency, as more of the hot gas path energy will be available for useful work.


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Again, parts commonality with hundreds of standard Avon units will be lost, and theuser, if incorporating the 200 modification will be restricted to replacing thesecomponents in the future with like, low production and expensive parts.

AlternativesOnce again, the application of highly effective thermal barrier coatings eliminates all theassociated problems with operating Avon units at elevated firing temperatures. Thesecoatings, when combined with intelligent minor revisions to the cooling regimens of theexisting turbine nozzle guide vanes, has performed very well in the field, and keeps totaloverhaul costs low.

- Combustion Liners and Fuel Injection Nozzles. (Swirler Burners.)With the failure of Rolls DLE combustion system for the Industrial Avon, which had beenunder development for over 12 years, Rolls has settled for a modest modification of thecombustion system by partially mixing fuel gas with a portion of the primary combustionair, via a hole in the fuel nozzles.

Advantages/DisadvantagesClose examination of the claimed benefits of the 200 Modification swirler burners, inthe product brochure shows that no change in NOx emissions is expected, yet in thenumbers posted a modest increase is indeed shown. This is simple combustion physics, aswith a diffusion type fuel nozzle, which the swirler burners are, NOx is a function offiring temperature and residence time in the combustion zone. As these two parametersare not changed, NOx production volume cannot change. Therefore, any increase in firingtemperature, will result in an increase in NOx production. Again, CO production is inversely

proportional to NOx production in a diffusion nozzle type combustor. It is to be expectedthat CO production will drop, with an increase in firing temperature, and any Rolls Royceturbine model that fires hotter than the Industrial Avon, (RB-211, Spey.) shows acorrespondingly lower CO production exhaust emissions signature.Currently, the world focus is on CO and CO2 emissions, however the production of NOx isnot to be forgotten, and indeed is much more serious of a threat to the environment.It is mandatory that the 200 modification combustion system be incorporated into thecustomers engine at time of overhaul. You cannot choose to take only this or that part ofthe modification, rather, you must take the whole kit whether the operator really needsall of it or not. These one-off combustor components have no commonality with the restof the worlds fleet of Industrial Avon units, thus will be expensive when replacement orrefurbishment is required at overhaul interval.

AlternativesThe Triple Dish type combustors, when coupled to flow balanced fuel injection nozzleshave demonstrated excellent overhaul life. In a pinch, even Mk-1535 operators can use theold style combustors and still operate reliably, so long as combustor loading is addressed.Once again, this is a case of keeping proven components in service, with the intelligentapplication of thermal barrier coatings, innovative refurbishment techniques, and keepingthe 1f vibration signature of the engine as low as possible, via correct rotor balancing.These together result in a combustion system that runs reliably for the whole overhaul

interval, and are readily refurbished at such overhaul.Should reduced emissions be the goal, there are commercially available lean-premixcombustors available for the Industrial Avon, that retrofit to the original engine cases, andfuel control systems. These lean-premix combustors offer significantly reduced NOxexhaust emissions , as well as reduced CO/CO2 emissions, and can be incorporated into


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any Industrial Avon unit without having to buy into a whole upgrade package that maybe cost prohibitive.

Conclusions

It is commendable that Rolls Royce has elected to keep the Industrial Avon product linesupported for an indefinite period of time. Most significantly, the downstream powerturbine assemblies have been upgraded and improved to give dramatic increases in outputand thermal efficiency, much more so than all of the model upgrades to the actualengines.The Model changes over the years, from Mk-1533 to Mk-1535 have been significant, butmost importantly, have been evolutionary, maintaining commonality with the lower output

model designations. Today, you literally, can take an early 1960s commercial Mk-533flight hot gas path engine component, and it will still physically fit into a Mk-1535 unit.This is not to say it will perform as well, but demonstrates the point of commonality. Thishas kept the Industrial Avon units cost competitive, and maintained a low total overhaulcost per fired hour.What Rolls Royce now proposes with the 200 modification, is a step away from thiscommonality, sharply driving up total overhaul costs, and most significantly, will keepthese units high in terms of total maintenance costs per fired hour.

Current Avon unit overhaul costs, when the 200 modification package is taken, are

averaging approximately $3.0M USD.At less than 60% of this cost, any Industrial Avon unit operator should have the option ofhaving their Avon engine assemblies overhauled, and demonstrated on the test cell, withwhichever particular suite of hot section, or combustor section upgrades incorporated intotheir engine that best suits their operating conditions and duty cycles. Anything less shouldnot be tolerated.

Many advances have been made over the last 15 years in terms of corrosion resistantcoatings, maintenance techniques, thermal barrier coatings, and base component alloys,giving turbine engine operators a wide choice of options when it comes time to performheavy maintenance to their units. A break from the OEM maintenance depots opens the

doors to these options. Operators owe it to themselves to check out these maintenanceoptions, as their competitors certainly are.

Author;

Robin C. Sipe; Founder, S&S Turbine Services Ltd.

S&S Turbine Services Ltd. is a fully independent turbine engine overhaul and test

acility, supporting General Electric, Rolls Royce and Solar product lines, in Marine,

Industrial and Military flight applications. Facilities located in British Columbia,

Canada. http://www.ssturbine.com

Re: Comments on the Avon "200" upgrade package.by robert.wallace

Unforunately, the author below has stated a number of inaccuracies in his comments thatneed to be corrected for the record. Rolls-Royce's David Taylor, Director of Technical

Posted: Mon Aug 24, 2009 12:16 pm
http://www.ssturbine.com/


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Servcies, has provided corrections in the author's comments below.

Robert Wallace, Rolls-Royce [email protected]

Comments on the Avon "200" upgrade package.by j79guy on Tue Mar 03, 2009 9:00 pm

I was asked to comment on the Avon "200" upgrade package that Rolls has available forthis product line. Here goes, I don't suppose I'll be getting a Christmas card.

Economic Alternatives to the Rolls Royce Avon "200" Modification Program

Background

Rolls Royce has recently announced what they describe as a significant upgrade to theIndustrial Avon gas turbine product line, promising; 1) Improved output. 2) Improved fuel

efficiency. 3) Reduced exhaust emissions. 4) Improved overhaul life. 5) Reduced overhaulcosts.

The following is an examination of these claims, based upon field and overhaul experiencewith the Industrial Avon product line, as a fully independent heavy maintenance andoverhaul depot, without any affiliation to Rolls Royce, and an offer of economicalalternatives:

An overview of the "200" modification revisions:- DS cast Hp. Turbine Blades. (Hpt Blades.)

- Hpt Blade tip sealing, and Tip Shrouds.- Hp. Turbine Disk and Blade root interface.- Metallurgy, Ip and Lp Turbine Blades.- Turbine Nozzle Guide Vanes. (Turbine Nozzles.)- Combustion Liners and Fuel Injection Nozzles. (Swirler Burners.)

Let us now discuss each of the modification revisions as per above.

- DS cast Hp. Turbine Blades.Improved, or really, increased output, for any gas turbine engine is strictly a function ofincreased airflow, (Mass flow.) or increased firing temperature. (Expansion ratio.)

As Rolls Royce is not proposing an increase in mass flow, then they are proposing toincrease the output via increased firing temperature only.

[Taylor, David H] Actually the writer is wrong. The mass flow is increased as the rotorspeed is increased. The average measured power increase is 11.5%, measured over 10engines. Interested parties can contact Rolls-Royce for a copy of this data if required.

To do this, Rolls has changed the turbine blade materials to allow an increase in firingtemperature. The root of this change is in the Hp Turbine Blades, which have been

changed to single crystal cast. (As opposed to equiax cast in the "regular" Avon engines.)Rolls Royce commercial RB211 aero engine experience has demonstrated the ability of SCcast blades to better resist creep growth than equiax cast blades, when comparing, similarcooling regimens of like blades, and the only difference is the casting technique. Rolls,with the "200" modification has eliminated the cooling air used to keep Hpt blade
mailto:[email protected]


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temperatures under control, and has elected to use solid blades, similar to the Mk-1533Hpt blades. Thus, when at full power, or increased power as proposed by Rolls, the Hptblades will in fact be operating at significantly higher temperatures than in Mk-1535engines.

[Taylor, David H] Wrong again. Due to the increased turbine efficiency the turbinetemperatures actually decrease. The addition of improved materials allows the HP coolingto be deleted thus further improving the cycle efficiency.

It must be clearly understood, that in order to achieve this increased output, that thefiring temperature of the engine must be raised, stressing not only the engine higher, butalso significantly, the downstream equipment will be subjected to higher thermal andtorsional stresses as well. As the Hpt blades are non-air cooled the operating temperatureof the blades will be much higher than in the "regular" Avon engines, and the Hpt Stage-1Disk will also be operating at a higher temperature as, the blades will be solely cooledthrough their roots into the disk.

[Taylor, David H] Wrong see above comment.

Advantages/DisadvantagesThermodynamic laws dictate that any increase in firing temperature will indeed result inhigher engine output and higher fuel efficiencies, so long as the customer's equipment canreliably take advantage of this increased output. What is not indicated in the Rolls RoyceAvon 200 brochure, is that if increased outputs are used, that the overhaul life of thedownstream equipment, particularly the power turbine assembly, may be reduced, andresult in higher overhaul costs per fired hour. If the end customer is operating theirequipment in an environment where local ambient temperatures are high, then increasingthe output of the package may not be practical, due to higher thermal loads that will need

to be radiated through the oil coolers.

[Taylor, David H] Wrong again. At base load power the power turbine entry temperatureactually drops by 40 degree C, thus the power turbine life is not reduced.

As the Avon 200 Hpt blades are not coated with any thermal barrier type coatings, theseblades will run at much higher temperatures than the "standard" Avon Hpt blades. Despitethe claims of Rolls Royce, who has yet to accumulate any significant run hours with anyAvon engine with the "200" modification it is highly likely that these blades will require asignificant percentage of replacement at each overhaul period, making such overhaulsextremely expensive. Single Crystal casting techniques have on average 60%-80% bladerejection rates during their manufacture, which is the primary reason they are so veryexpensive to purchase, or replace.

[Taylor, David H] Wrong again. See above comments on turbine temperature. The fleetleader has completed over 15,000 hours and there are now over 150,000 hours with noproblem being experienced. Scrap rate for single crystal blades is similar to that for equiaxblades.

AlternativesShould the end use customer require additional power from their package, and the

downstream equipment can reliably utilise this extra power potential, the application ofceramic thermal barrier coatings to existing equiax cast blades has been proven to be anextremely effective and economical solution to reduce the thermal loads on the Hp TurbineStage-1 disk assembly. For each Mil of ceramic coatings, the base metal temperature ofthe blading is reduced by 40 degrees C.


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A second, slightly more costly option (But a fraction of the total cost of the Avon 200 HptBlades.) is to use Directionally Solidified (DS) cast blading, available competitively priced tothe original equiax cast blades. DS casting is nearly as effective as single crystal casting interms of creep growth resistance, and they retrofit directly into the customer's engine,with no other costly modifications required. A set of DS cast, Hp Turbine blades, withceramic thermal barrier coatings will likely last the life of the engine, never requiringreplacement, and in the event that a DS cast blade does require replacement due to someother reason, they are available cost competitive to "standard" blades. To date, no Avon

Hp Turbine DS Cast blade, when combined with a ceramic thermal barrier coating, hasever needed replacement due to thermal distress or creep growth beyond acceptablelimits.

[Taylor, David H] The authors initial premise is totally incorrect. The A200 has a far moreefficient turbine which runs the engine faster thus increasing mass flow. The increase incomponent efficiencies allows the actual firing temperature to decrease by 29 deg C. Thusthe power turbine and gas generator turbines actually run cooler, thus increasing life. Thehigher temperature capability of modern SC materials allows us to eliminate HP turbinecooling. We have been running single crystal materials in the RB211 for several years and

the overhaul costs are comparable to equiax materials.

It would appear that the writer has some affiliation with a supplier of reverse engineeredturbine blades and his comments could be considered as marketing for those ideas. Rolls-Royce is not aware of any Avon operators running the blades described and the claimsmade are unlikely to be substantiated.

- Hpt Blade tip sealing, and Tip Shrouds.Rolls, with the introduction of the "200" modification, has revised the Turbine blade tipsealing and shrouds. The theory is that via revised blade tip sealing, gas path losses can be

reduced at the blade tips. To achieve this, Rolls has revised the blade tip "fences", and themating, stationary tip shrouds.

Advantages/DisadvantagesReduced turbine blade tip leakage is undeniably an objective in maximising hot gas pathenergy, and transforming it into useable work. On paper, the revisions made by Rolls inthe "200" modification appear to be a step in the right direction, however one must takeinto consideration as a whole, the operating of industrial Avon units, and the effectivenessof such modifications in light of long term operations. Avon units, in their "standard"configuration have shrouded blade tips, which is the single most significant step towardsimproved turbine cycle efficiency, as compared to traditional General Electric type blades,

which do not have such turbine blade tip shrouds. GE, in an effort to minimise hot gaspath losses, elect to run their turbine tip clearances extremely tight, and use abradeabletip shrouds to allow the blades to actually touch the stationary seals. It is common practiseto have to "break in" a freshly overhauled GE engine, as the turbine blades run on the tipshrouds quite hard, and upon first shutdown, may indeed "lock" the turbine rotor fromturning for several hours.Avon units, on test cell operation, have as part of their acceptance tests, a timed coastdown from the cut of fuel to the engine, from idle speeds. If the engine fails to meet aminimum run down time, the engine cannot be released to the customer. This is exactlythe opposite to General Electric philosophy, where "tighter, is better", and their engines

are expected to stop very quickly on test cell shutdown.

In order to meet this minimum run down time, Rolls elects to assembly the Avon units withgenerous turbine blade tip clearance, which limits the ultimate effectiveness of such.


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Therefore, no matter what revised system Rolls elects to incorporate into the Avonproduct, without changing the break-in procedure on the test cell, or altering theminimum run down time, there is a distinct limit to the effectiveness ofrevised tip shrouds.

[Taylor, David H] Incorrect. The A200 clearances have been selected and tested to give theoptimum sealing. The seal design is based upon that used successfully in the RB211 formillions of hours.

AlternativesInstead of electing the pay the premium price of the "200" modification, which includesrevised turbine blade tip shrouds and stationary seals, it is more economical to incorporatestationary tip shrouds that have an abradeable surface (Typically an unfilled honeycombtype sealing surface.), together with extended turbine blade tip "fences", which can beadded to "standard" blades during overhaul. During test cell running, the unit is run insequentially, to gently wear the turbine components in to each other, minimising hot gaspath blade tip leakage. Such is significantly more effective than the "200" modification,and is completely refurbishable at major overhaul intervals, at considerably less expense

than what Rolls presents to their customers.

[Taylor, David H] Tip rubs are a known cause of turbine blade vibration which can lead tofailure, unless the blade is designed to rub. Pre Avon 200 blades are not designed for thatcriteria.

- Hp. Turbine Disk and Blade root interface.With the Avon "200" modification program, Rolls has revised the Hpt blade root profile,and the mating Hpt disk assembly, which holds said blades.

In the past, Rolls has experienced failure of the Hpt disk and/or Hpt blades at the fir-treeroot interface, and thus has elected to revise the fir tree root profile on the promise ofbetter fatigue resistance.

Advantages/DisadvantagesOn the surface, revision of the Hp turbine root profile appears to be a good modification,however one needs to examine the past modes that led to the failure of the Hp turbinecomponents; It has been demonstrated that the failure of these components was in nearlyevery case, caused simply by uneven combustor (Flame tube) loading. This uneven loadingin turn, was caused by uneven fuel flows into the combustors, or a disruption of thecombustion process in each combustor. Revision of the Hp turbine components, althoughmay lead to a reduced incidence of failure, however this is treating the symptom, not thecause. As with all Roll Royce turbine products that have separate combustor cans, (Can-annular combustion.) it is imperative that the fuel flows into each combustor must bebalanced and even. By flow matching the fuel injection system components andmaintaining this system integrity, the incidence of Hpt turbine component failure iseliminated. (Those failures associated with uneven combustor loading.)

By incorporating the "200" modification, the customer is cutting themselves off from thetraditional supply of commonly available "standard" turbine components and committing tounique turbine components that have yet to prove their ultimate effectiveness and

longevity. Pricing of these new type turbine components have already been demonstratedas being extremely high.

[Taylor, David H] The revised root fixings and turbine blade design have been carefullydesigned using the latest techniques to eliminate HCF failures. Thus the through life


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costing of the A200 is cheaper by eliminating these costly failures. Interesting commentson pricing. If the writer had contacted Rolls-Royce for comparative costs he would havefound the A200 parts are very similar to pre A200 parts.

AlternativesThis fuel system flow matching can be done during engine overhaul at very low cost to thecustomer, and over the overhaul life of the engine, periodically checked during routineborescope inspection to keep the negative effects to a minimum. A spare set of flow

matched fuel injection nozzles, (Burners.) can be rotated into the unit during routineinspection. The removed fuel nozzles are then sent to depot for cleaning, and flowbalancing, which ensures the customer always has the lowest possible combustor loading,and subsequently reduced turbine system component stress. The original type Hp turbinecomponents are retained, and reliably operate over the life of the unit, without incurringthe expense of perhaps needlessly replacing such, with the goal of "fixing" a problem whichmay not exist.

[Taylor, David H] All burners are flow tested during overhaul and the flows must meetprecise criteria. Burner flows cannot be checked by boroscope, only by checking on a

calibrated flow bench.

- Metallurgy, Ip and Lp Turbine BladesWith the Avon "200" modification program, Rolls Royce has altered the base alloy of the Ipand Lp turbine blade materials. The claim is improved component longevity and overhaulcosts.

Advantages/DisadvantagesUpgrading the base alloys of the Ip and Lp turbine blades, is potentially a good idea, asalloys have advanced considerably in the last 15 years, giving better thermal creep growth

life, and resistance to hot gas path corrosion effects. However, the Rolls Royce IndustrialAvon units typically do not have a problem with the Ip and Lp turbine blades. The coatingsspecified for "standard" Avon units is a very mature specification, dating back to the early1960's. Currently there are a great many coatings available that offer vastly superiorperformance to the "standard" OEM coating, at economical pricing. It is most unfortunatethat the Avon "200" specification Ip and Lp. Turbine blades cannot be slowly incorporatedinto the Avon product line during overhauls as required, rather than a single, expensive,mass change out.

[Taylor, David H] The coatings chosen are Sermaly J. This offer the best corrosionresistance/price/reparability of any coating. There are more expensive coatings like

Platinum Aluminide but these are not required at the turbine temperatures experienced inthe Avon turbine.

AlternativesThe application of modern corrosion and thermal resistant coatings to the "standard" Ipand Lp turbine blades, offers as much, or better of a component longevity advantage asthe expensive "200" specification blades. Should the customer require increased engineoutput, then the application of ceramic thermal barrier coatings to these blades offersmuch more to the end customer in terms of reduced overhaul costs.

[Taylor, David H] The coatings used on the Avon 200 are the same as those on pre Avon200 turbines. Ref the comment regarding TBC, see earlier comment about reverseengineering.

- Turbine Nozzle Guide Vanes.


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Minor revisions to the turbine nozzles to allow a reduction in cooling air flow, and increasevane segment rigidity.

Advantages/DisadvantagesAny reduction in cooling air flow to the turbine nozzles will result in an increase in turbinecycle efficiency, as more of the hot gas path energy will be available for useful work.Again, parts commonality with hundreds of "standard" Avon units will be lost, and the user,if incorporating the "200" modification will be restricted to replacing these components in

the future with like, low production and expensive parts.

[Taylor, David H] See above comments on parts pricing.

AlternativesOnce again, the application of highly effective thermal barrier coatings eliminates all theassociated problems with operating Avon units at elevated firing temperatures. Thesecoatings, when combined with intelligent minor revisions to the cooling regimens of theexisting turbine nozzle guide vanes, has performed very well in the field, and keeps totaloverhaul costs low.

- Combustion Liners and Fuel Injection Nozzles. (Swirler Burners.)With the failure of Rolls' DLE combustion system for the Industrial Avon, which had beenunder development for over 12 years, Rolls has settled for a modest modification of thecombustion system by partially mixing fuel gas with a portion of the primary combustionair, via a "hole" in the fuel nozzles.

[Taylor, David H] Wrong. The writer has completely misunderstood the design of theswirler burner.

Advantages/DisadvantagesClose examination of the claimed benefits of the "200" Modification "swirler burners", inthe product brochure shows that "no change in NOx emissions is expected", yet in thenumbers posted a modest increase is indeed shown. This is simple combustion physics, aswith a diffusion type fuel nozzle, which the "swirler burners" are, NOx is a function offiring temperature and residence time in the combustion zone. As these two parametersare not changed, NOx production volume cannot change. Therefore, any increase in firingtemperature, will result in an increase in NOx production. Again, CO production is inverselyproportional to NOx production in a diffusion nozzle type combustor. It is to be expectedthat CO production will drop, with an increase in firing temperature, and any Rolls Royceturbine model that fires hotter than the Industrial Avon, (RB-211, Spey.) shows a

correspondingly lower CO production exhaust emissions signature.Currently, the world focus is on CO and CO2 emissions, however the production of NOx isnot to be forgotten, and indeed is much more serious of a threat to the environment.

It is mandatory that the "200" modification combustion system be incorporated into thecustomer's engine at time of overhaul. You cannot choose to take only this or that part ofthe modification, rather, you must take the whole "kit" whether the operator really needsall of it or not. These one-off combustor components have no commonality with the restof the world's fleet of Industrial Avon units, thus will be expensive when replacement orrefurbishment is required at overhaul interval.

[Taylor, David H] Wrong. The swirler burner has been the standard for several years andwas first introduced in the mid 1990's. Many operators have changed to the swirler burnerand have benefited from the ensuing benefits.


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AlternativesThe "Triple Dish" type combustors, when coupled to flow balanced fuel injection nozzleshave demonstrated excellent overhaul life. In a pinch, even Mk-1535 operators can use the"old" style combustors and still operate reliably, so long as combustor loading is addressed.Once again, this is a case of keeping proven components in service, with the intelligentapplication of thermal barrier coatings, innovative refurbishment techniques, and keepingthe 1f vibration signature of the engine as low as possible, via correct rotor balancing.These together result in a combustion system that runs reliably for the whole overhaulinterval, and are readily refurbished at such overhaul.

Should reduced emissions be the goal, there are commercially available lean-premixcombustors available for the Industrial Avon, that retrofit to the original engine cases, andfuel control systems. These lean-premix combustors offer significantly reduced NOxexhaust emissions , as well as reduced CO/CO2 emissions, and can be incorporated intoany Industrial Avon unit without having to buy into a whole "upgrade package" that may becost prohibitive.

Conclusions

It is commendable that Rolls Royce has elected to keep the Industrial Avon product linesupported for an indefinite period of time. Most significantly, the downstream powerturbine assemblies have been upgraded and improved to give dramatic increases in outputand thermal efficiency, much more so than all of the model upgrades to the actualengines.The Model changes over the years, from Mk-1533 to Mk-1535 have been significant, butmost importantly, have been evolutionary, maintaining commonality with the lower outputmodel designations. Today, you literally, can take an early 1960's commercial Mk-533 flighthot gas path engine component, and it will still physically fit into a Mk-1535 unit. This is

not to say it will perform as well, but demonstrates the point of commonality. This haskept the Industrial Avon units cost competitive, and maintained a low total overhaul costper fired hour.

What Rolls Royce now proposes with the "200" modification, is a step away from thiscommonality, sharply driving up total overhaul costs, and most significantly, will keepthese units high in terms of total maintenance costs per fired hour.Current Avon unit overhaul costs, when the "200" modification package is taken, areaveraging approximately $3.0M USD.

[Taylor, David H] Wrong again. The writer clearly has not researched the costs ofupgrading to Avon 200.

At less than 60% of this cost, any Industrial Avon unit operator should have the option ofhaving their Avon engine assemblies overhauled, and demonstrated on the test cell, withwhichever particular suite of hot section, or combustor section upgrades incorporated intotheir engine that best suits their operating conditions and duty cycles. Anything less shouldnot be tolerated.

[Taylor, David H] Wow. 60% x $3 million USD is an expensive overhaul for an Avon engine.Rolls-Royce authorised overhaul bases can provide a much more competitive price and have

OEM backing.

Many advances have been made over the last 15 years in terms of corrosion resistantcoatings, maintenance techniques, thermal barrier coatings, and base component alloys,giving turbine engine operators a wide choice of options when it comes time to perform


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heavy maintenance to their units. A break from the OEM maintenance depots opens thedoors to these options. Operators owe it to themselves to check out these maintenanceoptions, as their competitors certainly are.

[Taylor, David H] Ask Rolls-Royce for an Avon 200 quote for comparison. Then choose.

Re: Comments on the Avon "200" upgrade package.by robert.wallace

[Taylor, David H] One additional correction. The writer clearly does not understand thefunction of TBC. This only functions on 'cooled' parts where the coating slows the heattransfer rate. On uncooled parts it gives no benefit at all, with the blade reaching exactlythe same temperature as non TBC blades, thus TBC is a waste of money on IP and LPblades.

Re: Comments on the Avon "200" upgrade package.byj79guy

Thank you gentlemen, for responding to my comments regarding the Avon200 "upgrade"package. As I picked up your responses late in the evening, I will offer responses to yourcomments in a day or so, as time allows.

First off, I will respond to the last comment that TBC coatings do not function on"uncooled blades". Clearly Mr. Taylor does not understand how turbine blades are cooled.All turbine blades are cooled, whether they have internal air passages or not. Inconel 738would not survive the inlet temperatures of even a Mk-1533 Avon at base load, if theywere not cooled through the blade roots into the HPT disk. The purpose of TBC coatingstherefore is not solely to protect the blades as is commonly misunderstood, rather, it is to

protect the HP Turbine disk, by reducing the heat flux rate into the disk. To demonstratethe effectiveness of TBC coatings on solid turbine blades, I contracted Dr. Richard Stuber,(Who incidentaly worked on the design of various Industrial Avon HP Turbine Blades duringhis tenure with Rolls Royce.) to set up a burner rig to test the effectiveness of solid bladeswith various coatings applied, including no coatings. (Bare blades.) We measured thetemperature of the blades at several locations on each blade profile, as well as the disk tomeasure this heat flux rate, and to verify, or deny the effectiveness of such coatings. Ican post the results on this website should there be interest. Yes, the TBC coated bladesresulted in significantly lower blade and disk temperatures, both in heat transients, and inthe total heat load over time.

[Taylor, David H] Actually the writer is wrong. The mass flow is increased as the rotor

peed is increased. The average measured power increase is 11.5%, measured over 10

engines. Interested parties can contact Rolls-Royce for a copy of this data if required.

I am glad to hear that the increased power claims are made via higher engine speeds, asthis is not clear in the published Avon 200 brochure. Now we have something new todiscuss, in particular the increased stresses incurred with these higher operating speeds.I would suggest reviewing the Mk-1535 Avon compressor map, as at full speeds @ ISOconditions the compressor is already well past it's "sweet spot" in terms of efficiency. (The

compressor was aerodynamically "fixed" back with the introduction of the Mk-533commercial flight engines in the early 1960's, and no major aerodynamic revisions havebeen made since.) Any additional speed will be in the area of rapidly diminishingefficiency, and also increase stress the compressor rotor components, in particular the LPStages which already tax the limits of the aluminum LP blading strength. I'm surprised that

Posted: Tue Aug 25, 2009 6:21 am

Posted: Thu Aug 27, 2009 9:13 pm


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much power is made by an increase in speed, as the mass flow is not linear to the rpm atthe high rpm end due to the rapid fall off of compressor efficiency. The majority of theclaimed output increases is in higher mass expansion ratio, via higher firing temperatures.

Robin Sipe


[Taylor, David H] Wrong again. Due to the increased turbine efficiency the turbine

temperatures actually decrease. The addition of improved materials allows the HP

cooling to be deleted thus further improving the cycle efficiency.

You are saying that at 11.5% increased output over that of the Mk-1535 Avon @ Base Loadconditions, the turbine temperatures actually decrease? Myself, and I am sure most of thepeople who may be interested in this topic, would like to view the test data collected fromthe test engines, in the development of the Avon 200 "upgrade". (Not simulated or virtual

data, but rather the actual hard numbers collected during test running.) In order toacheive the claimed output and efficiency improvements, in light of diminishingcompressor efficiency at the higher rpm ranges, this equates to fantastic gains in overallturbine cycle efficiency. Bravo to the engineers who did the design work if the numbersare real, but I'm still sceptical, as the thermodynamic laws would nearly need to be bent inorder to acheive these results. Until I can view convincing data, I will stick to mystatement that the claimed output gains will be via increased mass expansion ratio, viaincreased firing temperature, which includes higher operating temperatures for the HP, IPand LP Turbine components.

[Taylor, David H] Wrong see above comment.

Ditto

[Taylor, David H] Wrong again. At base load power the power turbine entry temperature

actually drops by 40 degree C, thus the power turbine life is not reduced.

Thank you for clarifying the point. I am sure the customers will be happy to know that so

long as they do not use the increased power potential of their "upgraded" Avon 200 unitsabove base load conditions of their old Mk-1535 units, their power turbines will not bethermally overstressed.

Robin Sipe.


[Taylor, David H] Wrong again. See above comments on turbine temperature. The fleet

leader has completed over 15,000 hours and there are now over 150,000 hours with noroblem being experienced. Scrap rate for single crystal blades is similar to that for

equiax blades.

To be taken seriously in the industrial gas turbine marketplace, any turbine unit must

Posted: Thu Aug 27, 2009 9:40 pm



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operate at lease 30,000 fired hours between major overhauls, or they are not seriousplayers. The traditional Avon units have been the industry benchmark in terms ofreliability, and it is this reliability that I would not wish to see compromised by a so called"upgrade" program, that is as yet in it's infancy. 15,000 fired hours is shy of two yearsoperation, not exactly yet a proven package that a company should pin it's product linefortunes on, nor present to it's customers as a fully mature, well sorted package.It think there is a misunderstanding regarding scrap rates for cast blades. During casting,Single Crystal blades have a much higher rejection rate than equix cast blades, thus the

higher cost for SC blades.We know what equiax HP Turbine blades retail for, what is the retail for RR SC HPTblades? This is a road well beat by the independents who have developed their own DS andSC blades for the Avon product line, and it took several years to get the rejection rateslow enough to offer DS and SC HPT blades competitively to equiax cast HPT blades. (Theyare now being offered at less than equiax cast HPT blades.) These non-aircooled bladesretrofitted to a MK-1533 in conjuction with ceramic thermal barrier coatings are aneconomical alternative to the Avon 200 "upgrade" SC blades, within striking distanceefficiency-wise.

Robin Sipe.


[Taylor, David H] The authors initial premise is totally incorrect. The A200 has a far

more efficient turbine which runs the engine faster thus increasing mass flow. The

increase in component efficiencies allows the actual firing temperature to decrease by

29 deg C. Thus the power turbine and gas generator turbines actually run cooler, thus

increasing life. The higher temperature capability of modern SC materials allows us to

eliminate HP turbine cooling. We have been running single crystal materials in theRB211 for several years and the overhaul costs are comparable to equiax materials.

It would appear that the writer has some affiliation with a supplier of reverse

engineered turbine blades and his comments could be considered as marketing for those

ideas. Rolls-Royce is not aware of any Avon operators running the blades described and

the claims made are unlikely to be substantiated.

So long as the extra power potential is not used. Which is it, 29 deg C. or 60 deg C.? Inelectrical generation utility, where the operator is running to the limit of his generator

assembly, an increase in turbine cycle efficiency will result in a reduction in firingtemperature. How much gain in N1 speed is doubtable in light of diminishing compressorefficiency at the higher speeds. You cannot have it both ways. You either have an outputgain at similar EGT, or a reduction in EGT at similar output, when engine efficieny isaltered. (Increased.)Yes using DS or SC HPT blades allows the elimination of wasted cooling air, but the diskrim temperatures will be higher than traditional MK-1535 HPT disks. Please do notcompare oranges to apples. RB211 is a completely different engine line than the Avon,designed from inception for aircooled HP Turbine components. The Avon was not. If youwish, we can compare say, a particular GE LM engine of similar construction, firingtemperature and mass flow to the Avon, which would give much more meaningfulcomparison data.

Perhaps my comments can be construed as marketing a competitive product to RR, so beit, as you are doing the same. I am responding to a specific request from an Avonoperator who asked my opinion of the "Avon 200" program, which I supplied. He



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subsequently asked to post my opinion here to see if it sparks some dialogue, which itseems to have. Let's keep this discussion going. I am sure that there are many interestedparties who wish to read both sides of the discussion.

I can post pictures of independently produced DS HPT blading, both in Air cooled and Non-air cooled configuration, with run time accumulated, if there is interest.

Robin Sipe.


[Taylor, David H] Incorrect. The A200 clearances have been selected and tested to give

the optimum sealing. The seal design is based upon that used successfully in the RB211

or millions of hours.

[Taylor, David H] Tip rubs are a known cause of turbine blade vibration which can lead

to failure, unless the blade is designed to rub. Pre Avon 200 blades are not designed for

that criteria.

I will address both these comments together as they are connected: First off, this is arather lofty statement. It is a well known and demonstrated fact that optimum turbineblade tip clearance, at full rated output, is just shy of zero. Without a truly abradeablehoneycomb type tip shroud, this optimum clearance cannot be achieved, as the blade tipfences will run in a non perfectly round track. I do not dispute that the RB211 has a goodturbine blade tip shroud sealing arrangement, but is it optimum? Certainly not. Usingother engine lines as a true basis of comparison, it is common for these other productlines to have turbine blade tip rubs on coast down, on the test cell during break inprocedures. This is expected and indeed desirable, as it qualifies that the turbine blade tip

clearances are tight, and are making their respective running tracks optimum. To havethe minimum coast down times that are specified for the Avon product line, there is slimchance that these tip clearances are as low as they can reliably be.

Turbine blade flexural frequencies and their excitation in first/multiple orders is a wellbeaten path. I am not proposing to use unmodified, out of the box Avon turbine blades,rather the logical modification of their respective tip fences to allow tip rubs intoabradeable honeycomb type tip shrouds during test cell break in. This is not anything new,and has been in practice for several years without any failures due to tip rub excitationvibration.

Robin Sipe.


[Taylor, David H] The revised root fixings and turbine blade design have been carefully

designed using the latest techniques to eliminate HCF failures. Thus the through life

costing of the A200 is cheaper by eliminating these costly failures. Interesting

comments on pricing. If the writer had contacted Rolls-Royce for comparative costs he

would have found the A200 parts are very similar to pre A200 parts.[Taylor, David H] All burners are flow tested during overhaul and the flows must meet

recise criteria. Burner flows cannot be checked by boroscope, only by checking on a

calibrated flow bench.

Posted: Wed Sep 09, 2009 7:12 pm



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All times are UTC - 7 hoursPage 1 of2

My point exactly. By addressing the root cause of the HCF failures, there is no incidence ofsuch failures happening, therefore, no requirement to replace expensive turbine disksneedlessly. I am not comparing Rolls pricing between traditional Avon turbine disks to theA200 disks. The whole underlining point of my critique of the A200 program is thatoperators of Avon gas generators may be better served by not having their enginesoverhauled and upgraded by shops that strictly use Rolls Royce as their sole source ofparts. There are less expensive alternatives.

I can only hope that this word gets out to the OEM affiliated shops that I have toured.None that I have seen have the flow testing equipment required for correct fuel flowbalancing. When Ive brought this to their attention, the usual answer is, It is notrequired. On the other hand, there are independent Avon shops who do have the correctequipment, and have identified on their own that the root cause of the majority of HCFfailures stems from uneven combustor loading. This is not limited of course to the Avonproduct line, rather effects all gas turbines with can type combustion liners, thus is appliedto these engines as well with success. The Marine/Industrial Spey product line come tomind as being especially critical in this area, with rather dramatic failures occurring due touneven combustor loading.

Robin Sipe.


[Taylor, David H] The coatings chosen are Sermaly J. This offer the best corrosion

resistance/price/reparability of any coating. There are more expensive coatings like

Platinum Aluminide but these are not required at the turbine temperatures experienced

in the Avon turbine.

[Taylor, David H] The coatings used on the Avon 200 are the same as those on pre Avon200 turbines. Ref the comment regarding TBC, see earlier comment about reverse

engineering.

I believe the correct name for the coating is Sermalloy J To state that Sermalloy J is thebest all-round turbine blade coating, at the turbine component temperatures seen withinthe Avon product line, is again a bit presumptuous. All other turbine manufacturers withproduct lines that operate with turbine component temperatures in a similar range to theAvon have it wrong? Seriously now, there have been really great advances made in theworld of turbine component coatings since Sermalloy J was introduced in the early 1960s,

and yes cost competitive too. Operators of Avon units only need to go to a fewindependent coating shops and obtain quotes to directly compare costs. Modern coatingsapplied to traditional Avon turbine components results in improved thermal efficiency, andcomponent life over old school coatings.

Regarding your comments on TBC; You dont really think that Mk-1533 Avon HPT bladesoperate at the same temperature as the gas inlet temperature do you? This is basicturbine thermodynamics. Reduce the heat flux rate into the blade, more heat is keptwithin the gas path, and disk(s) run cooler. Sir Frank Whittle had a full understanding ofthis in the 1930s.

Robin Sipe.

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