faq%20rejuvenation%202010
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Liburdi Turbine Services Inc March 2010 Frequently Asked Questions –
FSRTM Full Solution RejuvenationTM for Turbine Blades 1. Why do I need to apply the FSR
TMheat treatments to a blade set?
Over time the operating temperatures and stress loads cause the creep strength of the blade alloy todeplete. The alloy can also accumulate internal stresses due to cyclic operation (high cycle fatigue andlow cycle fatigue damage) which can lead to dislocations within the alloy micro-structure. When the bladeset reaches this point, the material properties need to be restored through FSR
TMRejuvenation heat
treatments in order to ensure continued reliability. 2. When do I need to have a blade set processed with FSR
TMFull Solution Rejuvenation
TM.
Typically it is at the point where the manufacturer states that the parts are “time limited” due to highservice hours and the FSR
TMRejuvenation is an alternative to retiring the blades from service. In fact
there is no set time or number of hours of operation for all blade models, or for all operating plants sinceeach operator may run the engines differently or under different conditions – For example desert or arctic
environment, max load, part load, daily start/stops etc. So in some cases Stage 1 and Stage 2 bladesets need to be rejuvenated every 24,000 hours in other cases every 48,000 hours, and Power Turbine(Stage 3, Stage 4 ) blade sets may not need to be rejuvenated until 100,000 hours. The alloy condition can be determined by performing a metallurgical remaining life assessment. Thisrequires that one blade from the set be destroyed to determine the creep strength and micro-structurecondition which is representative of the rest of the set. For many operators with good operating practices,the metallurgical assessment will also be representative of the other engines in the fleet. 3. How does the process work? Depending on the alloy, the blades may be processed through a series of high pressure (HIP) heattreatment followed by vacuum heat treatment cycles. For precipitation hardened alloys such as IN738,GTD111, Rene80 used in GE engines the strengthening element, called gamma prime phase, is first
dissolved or by taking the alloy to the “full solution” temperature for the alloy. While in this condition, thehigh pressure HIP treatment compresses or heals any creep voids or original casting porosity which maybe present. The subsequent vacuum heat treatments are then used to precipitate the gamma primephase back into the structure to restore the original micro-structure and alloy properties. 4. Some people claim that the HIP portion of the heat treatment is not beneficial.
Is this true? Sometimes there is some confusion as to why HIP is included in the process. It is true that HIP does notheal cracks that are present at the surface of the blade. It is not intended to do so; it is intended and isvery effective in healing internal voids and HIP has been used effectively for many years by the engineOEM’s to heal casting porosity as part of new blade manufacture. Cracks that are at the surface of theblade can be identified with conventional NDT methods and dealt with.
5. If HIP is used to correct internal voids and casting porosity, why use it for forged alloys? In some forged alloys creep voids may have formed in the alloy and the HIP process will close thesevoids and restore the integrity of the material. Also Liburdi, in developing its family of Full SolutionRejuvenation
TMheat treatment cycles, has found that certain alloys respond better after they have been
first processed with the high pressure HIP heat treatment to Liburdi Specs. When this is done thesubsequent vacuum heat treatments produce superior properties and alloy strength. 6. What is Liburdi’s experience with FSR
TMFull Solution Rejuvenation
TMof blade sets?
Liburdi was the pioneer in this practice and introduced the process some 30 years ago. Liburdi hasdeveloped Full Solution Rejuvenation
TMheat treat cycles for virtually all of the common blade alloys (eg.
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IN738, IN939, U500, U520, MarM002, MarM247, N115, N105, N108, A286, GTD111+DS, Rene80+DS),including the new DS directionally solidified cast blades. During this 25 year history, Liburdi hassuccessfully rejuvenated over 100,000 blades and has a track record of consistently reliable operation ofthese blades. 7. Do the engine OEM’s and other component repair shops authorize FSR
TMFull Solution
RejuvenationTM
heat treatments? Yes, for the past several years OEM’s such as Rolls-Royce , Westinghouse, and Dresser-Rand haveoffered the Full Solution Rejuvenation
TMprocess for their blades and in doing so have been able to
provide their operators reliable blade life extensions. All three of these OEMs have their bladesprocessed by Liburdi using our proven FSR
TMprocesses.
8. How are you assured that each blade set has responded to the heat treatments?Since we are restoring the original micro-structure of the alloy, we make it a practice to re-certify blade setin the same way that new parts are certified. To do this we include sample material of the same alloy(usually a scrap blade from the same set) in all heat treatments that the set receives. The samplematerial is then metallurgically re-certified by examining the micro-structure and performing creepstrength testing (stress rupture bars) which must meet or exceed the engine manufacturer’s specificationsfor new parts.
9. How long does the effect of the Full Solution RejuvenationTM last? Because the original alloy structure has been restored, typically the blades are operated for a similar timeperiod as when new (assuming similar operating conditions). For example if the new blades have beenoperated reliably for 60,000 hours, the rejuvenated blades would operate for a further 60,000 hours. Aftera suitable time period, the blades may be re-tested or rejuvenated again to ensure continued reliability. 10. Do you have actual service experience with blade sets operating for this period of time? Yes, because we have used the process for many years we have first hand experience with each alloytype. Early FSR
TMRejuvenation of Westinghouse and GE blades in pipeline service have achieved over
200,000 hours and have achieved a “3rd
life” after two FSRTM
Rejuvenation applications. Similarly, werejuvenate the newer, high efficiency power generation engines more than once. Due to the high firingtemperatures of these engines the Full Solution Rejuvenation
TMtakes place regularly each 24,000 hours
or 48,000 hours depending on the engine..
11. Specifically for the GE engines, what is your FSR
TMexperience?
For the aero-derivative – LM2500, LM1600 engines - Liburdi has rejuvenated over 100 blade sets since1997. These sets have been high hour and in most cases “time expired” by the OEM standards (withoutrejuvenation). All blade sets have been successfully returned to service after Full SolutionRejuvenation
TM.
For the industrial frame GE engines – Frame 3,5,6,7 - Liburdi has extensive experience for all modelsgoing back to 1990. Over this time, sets have been successfully operated for additional service intervalsand have achieved two times the previous GER3620 OEM life expectancy. Over this time period morethan 100 blade sets have been rejuvenated.
12. Specifically for the Rolls-Royce engines, what is your FSR
TM
experience? Rolls-Royce RB211 and Avon blade sets have successfully achieved 100,000+ hours of reliable service.For the RR Avon engine we have successfully rejuvenated over 400 sets of blades over the period from1994 to present. For the RB211 HPT and IPT blades we introduced the Full Solution Rejuvenation
TM
process in 1995. Since that time over 250 blade sets have been successfully rejuvenated and areachieving an additional two service intervals beyond the previous “time limited” standard for these blades.
Liburdi Turbine Services Inc
www.liburditurbine.com
tel 905-689-0734 fax 905-689-0739