ML19323G131

Forwards Request for Addl Info Re Cracks in Keyway & Bore Sections of Discs in Westinghouse Low Pressure Turbines. Summary of Related 800109 Meeting,Ie Info Notice 79-37 & Errata Encl

ML19323G131
Person / Time
Site:	Calvert Cliffs
Issue date:	05/15/1980
From:	Clark R Office of Nuclear Reactor Regulation
To:	Lundvall A BALTIMORE GAS & ELECTRIC CO.
References
NUDOCS 8005300428
Download: ML19323G131 (3)

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t WASHINGTO N, D. C. 2C555 h([ May 15, 1980 Do[leYNo. 50-317 Mr. A. E. Lundvall, Jr. Vice President - Supply Baltimore Gas & Electric Conany P. O. Box 1475 Baltimore, Maryland 21203

Dear Mr. Lundvall:

On December 28, 1979 the NRC Office of Inspection and Enforcement (IE) issued Information Notice No. 79-37 that discussed the discovery of cracks in the keyway and bore sections of discs in Westinghouse low-pressure turbines. A copy of this Information Notice with an errata sheet is enclosed. Subsequently, all licensee / users of low-pressure turbines manufactured by General Electric were invited to meet with the NRC staff and representatives of the vendor en January 9,1980 to discuss the probability of disc cracking in these turbines. A summary of this meeting and the General Electric Cogany's presentation are also enclosed with this letter. At the time of the January 9 meeting General Electric did not have any recent results of ultrasonic inspections of its low-pressure turbines. Since that date full UT inspections have been performed on six rotors at five nuclear power plants. y Scae indications in the keyway region have been reported in discs at three of these plants. General Electric personnel believe that these indications were caused by water erosion rather than by stress corrosion. The staff desires to learn more about the underlying reasons for the indications found and the probable rate of growth of thase indications and their effects on turbine disc integrity. For this purpose we request that you provide the information scught in Enclosure 3 to this letter and address its safety significance. Under the provisions of 10 CFR 50.54(f) your response is requested within 30 days of the receipt of this letter. A copy of this letter is being telecopied to you, along with Enclosure 3. It is my understanding that additional UT inspections are to be performed by General Electric in the near future. We encourage this action as being the only certain means of determining the integrity of turoine discs. We also recoranend that if you have not already done so, you develop a schedule for performing a full UT inspection of at least one of your low-pressure turbines during the nex. major outage of your plant. THIS DOCUMENT CONTAINS P00R QUAUTY PAGES 8005000 N

A = 1 This request for generic information was approved by GA0 under clearance number ~ B-180225 (S79014); this clearance expires June 30, 1980. Sincerely, Robert A. Clark, Chief Operatin. Reactors Branch #3 Divi sio-Licensing

Enclosures:

1. Information Bulletin 79-37 2. Meeting Summary 3. Information Requests cc: See next page O e =w e e v. a m r,, w --- -r,,-e-- -p- --n,

G I, F3 B'altimore Gas and Electric Company I '=-= 1 I

==_r T cc w/ enclosure (s): g Jarles A. Biddison, Jr. Mr. Bernard Fowler 55 General Counsel President, Board of County-

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G and E Building Commissioners Charles Center Prince Frederick, Maryland 20768 E5 ?.6_ Baltimore, Maryland 21203 Director, Technical Assessment iff George F. Trowbridge, Esquire 'Jivision M Shaw, Pi ttman, Potts and Office of Radiation Progratas 55 5 Trewbridge (AW-459) 55 I 1800 M Street, N.W. U. S. Environmental Protection Agency fff Washington, D. C. 20035 Crystal Mall #2 55 @I= Arling cn, Virginia 20460 Mr. R. C. L. Olson Baltimore Gas and Electric Company U. S. Enviromental Protection Agency EM .i Room 922 - G ano E sp uing Region III Office E Post Office Box 1475 ATTN: EIS COORDINATOR E Baltimore, Marylano 21203 Curtis Building (Sixth Floor) H Sixth and Walnut Streets M Mr. Leon B. Russell, Chief Engineer Philadelphia, Pennsylvania 19106 g !"5 Calvert Cliffs Nuclear ?ower Plant Baltimore Gas and Elect-ic Company Ralph E. Architzel 5 Lusby, tiaryland 20657 Resident Reactor Inspector M NRC Inspection and Enforcement EE Bechtel Power Corcoration P. O. Box 437 is. $[4 5 ATTH: Mr. J. C. Jude Lusby, Maryland 20657 Chief Nuclear Er.gineer 15740 Shady Grove P. cad Gaithe rsburg,11arylan d 20760 E i= Comeustion Engineering, Inc. Administrator, Power Plant Siting Program EE ATTN: Mr. P. W. Kruse, l'.anager

nergy and Coastal Zone Administration fi Engineering Services Department of Natural Resoarces E

Post Of fice Box 500 Tawes State Office Building E Windsor, Connecticut (60!'S Annapolis, Maryland 21204 5 F5 Calvert County Library Prince Frederick, l'.aryland 20678 [, ?: Director, Department of State Planning j J. 201 West Presten Stree: P. Baltiture, Maryland 21201 k= i ir Mr. R. M. Douglass, ".arager E: Quality Assurance Depar. ment i E Rocc 923 Gas 1 Electri: Building 5 P. O. Box 1 75 E; Baltircre, Maryland 21203 E 4 -. __ _.....r~ T:: .. r.- i

s 4 UNITED STATES ISINS NO.: 6870 NUCLEAR REGULATORY COMMISSION Accession No.: OFFICE OF INSPECTION AND ENFORCEMENT 7910250525. --- WASHINGTON, D.C. 20555 December 28, 1979 o IE Information Notice No. 79-37 CRACKING IN LOW PRESSURE TURBINE DISCS Description of Circumstances: An anonymous lettar was received by the Director of the Office of Inspection and Enforcement, on November 17, 1979 which allegeJ possible violation of Part 10 CFR 50.55e and/or 10 CFR 21 Regulations concerning reportability of recently discovered stress corrosion cracking in Westinghouse 1800 rps low pressure turbine discs. Westinghouse had made a presentation on the turbine disc cracking to electric utility executives on October 30, 1979. Telephone discussions between the NRC staff and Westinghouse's Turbine Division on November 20, 1979 established that cracking, attributed to stress corrosion phenomena, had been found in the keyway areas of several LP turbine discs at operating plants and that inservice inspection techniques (i.e., in situ ultra-sonic examinationJ for crack detection have been developed and are being imple-mented in the field. The Office of.'nspection and Enforcement was also notified on November 20, 1979 that during the carrent overhaul of Commonwealth Edison's Z!an Unit 1 LP turbine, ultrasonic examination revealed embedded cracks located on the inlet side on the disc bore area where no cracks had been previously observed. Ultrasonic measurements indicate this disc bore cracking is of greater depth than the keyway cracks found to date. According to Westinghouse, these bore cracks have been metallurgically examihed and preliminary findings show them not to be typical of classical stress corrosion cracking observed in the keyways. The probable cracking mechanism and impact on disc integrity is being further evaluated by Westinghouse. A meeting was held on December 17, 1979 between the NRC staff, Westinghouse ~ and utility representatives to discuss the disc cracking problem, repair alter-natives, turbine missile evaluation, inspection techniques and plant inspection priorities. In response to the staffs' request, Westinghouse provided the staff an updated report on December 21, 1979 regarding the current field inspection program that included a list of nuclear power plants already inspected, recom-mended inspection schedules and pertinent information related to LP turbines where cracks have been observed. Inspections to date have identified tut oine disc cracks at Surry Unit 2, Point Beach Unit 2, Palisades, Indian Point Unit 3 and Zion Unit 1. All units except Point Beach Unit 2 will make repairs before the plants return to power. Point Beach returned to power on December 23, 1979 with a small crack in the No. 2 disc of LP Turbine No. 2. An analysis by Westinghouse indicated that the observed crack will not attain critical dimensions during 28 additional conths of turbine operation. The NRC staff is evaluating the turbine inspection results and analysis by Westinghouse. l ~7 ' / c 2 70 5 4 5 e c

P l L l IE Information Notice No. 79-37 December 28, 1979 Page 2 of 2 I Westinghouse also notified the staff that extrapolation of information obtained from Indian Point Unit 3 inspection and analysis indicates that disc cracking could be significant at Indian Point Unit 2 and the turbines should be inspected sooner than the spring outap of 1980. The NRC staff is currently reviewing Consolidated Edison's plans for prompt evaluation of this potential problem at this unit. lists the PWR plants having Westinghouse 1500/1800 rpm turbines. The AA category represents those turbines which appear to have the earif est l need for inspection. With the exception of Yankee Rowe, Westinghouse has recommended to utilities that inspection of these machines be completed by the Spring 1980 outage period. The Rowe unit is uninspectable by the present ultrasonic techniques due to its design. Westinghouse has recommended the remaining machines of the Category A plants be inspected as their service periods approach five years or in the event significant corrosion problems become l evident during this time. The NRC staff is currently reviewing the need for inspection of those PWR plants havirq other interfacing turbine designs shown in Enclosure 2. Changes to the forementioned inspection schedules proposed by Westinghouse may be necessary as new technical information becomes available. From the information available to the NRC staff at this time it appears that cracking may be more generically widespread in turbine discs (e.g., keyways and bore areas) than previously observed. It is important to note that the UT inspections performed by Westinghouse thus far were essentially limited to the keyways (disc outlet) of selected discs whereas the Zion Unit 1 inspection results indicate that examination of the disc bore section must be taken into Also, Westinghouse is currently re-evaluating their previously estimated account. turbine missile energies based on recent missile test results from model symmetric and non-symmetric missile impact tests. Their preliminary findings, although subject to change, now indicate possible higher missile exit energies in some cases than previously expected. This Information Notico is provided as an early notification of a possibly significant matter, the allegations and the generic safety impffcations of which are currently undergoing review by the NRC staff. It is expected th M recipients will review the information applicable to their facilities. If NRC evaluations so indicate, further licensee actions may be requested or required. Embedded cracking in keyways 'and disc bore areas have been observed only in Westinghouse LP turbines thus far. However, the NRC staff believes that turbines of other manufacturers should be included in consideration of this problem.. No written response to this Information Notice is required. If you have any questions regarding this matter, please contact .:e Director of the appropriate NRC Regional Office.

Enclosures:

As stated - _ _ =.--

I e t ~~ CATEGORY AA UTILITY STATION UNIT Florida, P&L Turkey Point 3 consolidated ED. Indian Point 2 PASNY Indian Point 3 Arkansas P&L Russellville 1 VEPCO Surry 1 Carolina P&L Robinson 2 So Calif. Ed. San Onofre 1 Yankee A.P. Rowe 1 Wisc. Mich. Pwr. Point Beach 1 1 Consumers Pwr. Palisades 1 Commonwealth Ed. Zion 1 1 Commonwealth Ed. Zion 2 2 Florida P&L Turkey Point 4 Nebraska PPD Cooper 1 Wisc. Mich. Pwr. Point Beach 2 Maine Yankee Bailey Point 1 Rochester G&E Ginna 1 Northern States Prairie Island 1 Wisc. P.S. Kewaunee 1 l I 1 .winsi-,= y c,.,-,,-

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O .- (Continued) Page 2 of 3 CATEGORY A UTILITY STATION UNIT Alabama Power Farley 1 Alabama Power Farley E 5altimoreG&L Calvert Cliffs 2 Carolina P&L Harris 1 Carolina P&L Harris 2 Carolina P&L Harris 3 Carolina P&L Harris 4 Cincinnati G&E Zimmer 1 Commonwealth Ed. Byron 1 Commonwealth Ed. Byron 2 Commonwealth Ed. Braidwood 1 Connonwealth Ed. Bra.idwood 2 Connecticut Yankee Haddam Neck 1 Ouke Power McGuire 1 Ouke Power McGuire 2 Ouquesne Lt. Shippingport 1 Ouquesne Lt. Beaver Valley 1 Ouquesne 1.t. Beaver Valley 2 Flordi. 'ower Corp. Crystal River 3 Flordia Power & Lt. St. Lucie 1 Flordia Power & Lt. St. Lucie 2 Houston L&P So Texas 1 Houston L&P So. Texas 2 Louisiana P&L Vaterford 3 Metropolitan Ed. Three Mile Island 2 Northern States Pwr. Prairie Island 2 Pub. Service E&G Salem 1 Puo. Service E&G Sales 2 Pacific G&E Oiablo Canyon 1 Pacific G&E Diablo Canyon 2

i i , (continued) Page 3 of 3 CATEGORY A UTILITY STATION UNIT P.S. Indiana Marble Hill 1 P.S. Indiana Marble Hill 2 Puget Sound P&L Skagit 1 SMUD. Rancho Seco 1 TVA Sequoyah 1 TVA Sequoyah 2 TVA Watts Bar 1 TVA Watts Bar 2 VEPCO North Anna 1 VEPCO North Anna 2 VEPCO North Anna 3 VEPCO North Anna 4 VEPCO North Anna 2 WPPSS Hanford 2 WPPSS WNPS 1 WPPSS WNPS 3 WPPSS WNPS 4 WPPSS WNPS 5

UTILITY STATION UNIT Duke Power Co. Oconee 1 Ouke power Co. Oconee 2 Duke Power Co. Oconee 3 OPPD Ft. Calhoun 1 Baltimore Electric & Gas Calvert Cliffs 1 Metropolitan Edison Three Mile Island 1 Indiana & Michigan Electric D.C. Cook 1 Indiana & Michigan Electric D.C. Cook 2 Northeast Utilities Millstone 2 Portland General Electric Trojan 1 Toledo Edison Davis Besse 1 Arkansas Power & Light Arkansas Nuclear One 2

WPPSS, Hanford 1

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Errata Sheet For IE Information Notice No. 79-37 Page 1, paragraph 2, line 9: Change " inlet" to " outlet" Page 1, paragraph 3, lines 9 and 10: Change " Point Beach Unit 2" to

• Point Beach Unit 1" Page 1, paragraph 3, line 10: After Point Beach Unit I add an asterisk

("*") footnote and place a note at the bottom of the page as follows: " Wisconsin Electric Power Company orally notified the NRC project manager on November 5 that turbine disc cracking had been observed at Point Beach Unit 1.", line 4: Change "Russellville" to "ANO", line 8: Change to read: " Yankee Atomic Electric, Yankee Rowe", lines 9 and 15: Change '" disc Mich Pwr" to "Wisc Elec Pwr", line 16: Change to read " Maine Yankee Atomic Pwr, Maine Yankee", page 3, line 13: Delete as redundant reference to North Anna 2 l l l I l l l t %.px 5\\ 6CQ?>V/05foC e C

k---- bdb ng g 6 f'f. s-S, UNITED STATES . i *; T& CLEAR REGULATORY COMMISSION J..' 8 WASHINGTON. D. C. 20SSS a s, % / TE3RUA2Y : 1 2 5 ME:10RANDUM FOR: A. Schwencer, Chief Operating Reactors Branch #1, 00R FROM: W. J. Ross, Project Manager Operating Reactors Branch #1, 00R SUEUECT: MEETING WITH GENERAL ELECTRIC RELATED TO TURBINE DISC CRACKS At the staff's request, representatives of General Electric met with the staff and licensee / user of G.E. turbines on January 9,1980 to discuss the design of and operational experience of low pressure turbines. A list of attendees at the non-proprietary and proprietary sessions is attached. In the non-proprietary session General Electric's personnel discussed the follcwing topics: (a) turbine wheel (disc) integrity; (b) minimizing wheel (discs) bursts. Copies of the slides used in this presentation are attached in Enclosure 3. Turbine Wheel Integrity There has been no indication of cracks in the bore regions of G.E. Icw premtre turbine wheels. This experience includes the coeration of 35 turbines at nuclear generating plans (22 BWRs-of which only three have actually been inspected) and 4000 wheels at 235 fossil u'its (percent of wheels inspected was not established at the meeting). A G.E. turbine has the following design characteristics: (1) 14 wheels or discs per rotor with 38" or 43" active length buckets or blades. (2) Rectangular axial keyway and circumferential locking ring minimize rotation of wheels on the turbine shaft (i.e. minimize stress). (3) Feedwater systems on nuclear plants are provided with full-flow domineralizer, (experience with fossil plants nas Nen good even with poor water chemistry). General Electric referenced a 1973 memorandum that postulated the arcoa-bilities of turbine missiles as follcws: L _ k, e t,' ) S C O 5 l 0??O - d -

o l l 2-2.6x10j~ P (<127% normal turbine speed) = 1.5x10 P (runaway) 4.1x10~7 = P (lifetime total) 1.4x10~8 = ~ P (annual average) = General Electric continues to recospend that its users perform UT inspections of wheel bores at 6-year intervals. A satisfactory UT test has ben developed for this purpose. To date the three UT tes.s that have been performed were on nuclear turbines that had averaged about 3 years of operating experience. Minimizing Wheel Bursts A brief review of actions taken by G.E. to eliminate the formation of cracks in turbine wheels was presented and included the following:

1) Forging process designed to eliminate internal cracks.

2) New wheels are inspected by visual UT and magnetic particle techniques.

3) New wheels are tested at 1201 operating speed.

4) Tolerance o< defects caused by stress and corrosion maximized through chai ce of material.

5) Provisich for UT testing of wheels after installation and use.

General Electric's personnel provided the following responses to questions from the audience. Retention of a 6-year interval for inspection of turbines was 1. justified by operating experience and crack growth rate studies. 2. Three G.E. turbines at nuclear plants (1 ShR and 2 PWR) have been inspected by UT and no indications observed. These turbines had seen about 3 years of service. 3. All wheels of turbines at nuclear sites are inspectable in sites (without removal from the turbine). Approximately 5 days are required to inspect one 14-wheel rotor. Four adaitianal days would be needed to conq lete the inspection of a second rotor at the same site. 4. The length of a crack is postulated by G.E. to be 4 to 5 times the depth detemined by UT. 5. Overspeed devices on G.E. turbines are testable uncer load and retain their protective capability during the test. ..r.-,._,--- ,y .__.,,,,m.

3 6. The G.E. representatives were not aware of any custceer' ~ excerience where overspeed emergency systems have ever been used. J I 7. Minimum defect size observable by UT as practiced by G.E. is as small as 30 mils in new wheels. 8. G.E. has little data related to chemical analysis of deposits in cracks because few have been observed. Chloride has been observed in pin cracks. 9. Cosparisons of stress corrosion cracking between turbine discs (3.51 Mi Ci Mo V) and in 304 ss pipe are not appropriate because they have different fluids (water and steam) and different materials. 10. G.E.'s wheel keyways are not shielded from steam flow chemicals (Westinghouse is considering such protection)

11. Thermal and vibrational stresses on turbine wheels are censidered to be very small in comparision to design capability.

12. G.E. does not presently have specific teams of inspectors mobilized for inspecting turbines. v& dwL William J. Ross. Project Manager Operating Reactors Branch #1 Division Of Operating Reactors Attachents: Attendees Slides used in G.E. presentatien

t ATTENDEES ~.. GENERAL 5LECTRIC ~ flRC R. 5. Coucnman W. J~" Toss D. P. Timo R. E. Johnson J. J. Hinchey

• M. L. Boyle W. J. Kathier A. Taboada H. T. Watanase J. J. Zudans R. D. Brugge W. P. Gamill K. G. ura T. Ippolito W. J. Collins E. G. Arndt I. A. Peltier K. M. Cage F. Clemenson C. D. Seller M. Wohl R. W. Klecker K. R. Wichnen W. S. Hazelton V. Noonan

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e n vve_.. :r. e e r.n ~ ~ ~ UTILITY NAME Becntel Pcwer Corporation Eaul Nastick ~ . '.'P P S C. W. Hultman Portland General Electric J. E. McEwen Stone and Webster John Coombe American Electric Power Richard G. Kriftner Duke Power Comcany Paul H. Barton Northern States Pcwer Corgany Craig F. Nierade Otakar Jonas Westinghouse Consumers Power Company James B. Lewis Yankee Atomic Electric Coccany Robert L. Smith Jersey Central Power and Light Company Jfm Knuber Tennessee Valley Authority Larry A. Johnson Philadelphia Electric Company Norman H. Gaffin Martin J. McCornd ch, Jr. Philadelphia Electric Coapany Baltimore Gas and Electric Corpany L. Erik Titland Baltimore Gas and Electric Coepany Ronald O'Hara Baltimore Gas and Electric Coreany R. Niall M. Hunt Baltimore Gas and Electric Corgany R. G. C11 sham Omaha Public Power District S. F. Sinderup Metropolitan Edisen Company C. C. Seitz Commonwealth Edision Corgany P. K. Colvert Commonwealth Edision Company R. J. Tammi nga W. G. Cl a rt. J r. Westinghouse Westinghouse R. E. Warner Westinghouse V. S. Anderson Westinghou se

8. 8. Seth American Electric Power J. F. Etzweiler 1

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4 9 f 4 e e 9 e 9 Deme mon NUCLEAR STEAM TURSINE WHEEL REllABILITY

INTRCCUCTICN This paper deals with shrunk-on bucket wheels used in steam tu,roines - ~ ~ manufactured by the Large Steam Turbine-Generator Cepartment of General Electric for use with nuclear reactor cycles. In particular, General Electric's efforts aimed at avoiding a wheel burst as the result of stress corrosion cracking are described. These efforts include steam purity reconnendations, the use of optimum design, material selection and acceptance practices, and the. introduction of a computerized in-service wheel bore ultrasonic test. In Februa ry,1978, TIL-857 was issued outlining recommended in-service inspecticn practices for nuclear steam turbine rotors manufactured by General Electric. Recommendatiens include a ecmplete ultrasonic examination of the shrunk-on wheel bores at abcut 6-year intervals. OVERVIEW There are two possible mechanisms for initiating and/or growing cracks in nuclear wheels in service: 1. Stress Cycling 2. Stress Corrosion Cracking The likelihood of initiating and/or grcwing a crack due to stress cycling associated with starts, stops, or load changes is small. Variations in stress amplitude resulting from operating transients are too low to produce significant crack growth, in the unlikely event that a defect exists in the wheel when it is placed in-service. The manner in which wheels are forged essentially precludes the rassibility of producing an internal crack-like defect in the plane normal to thw.3ximum stress (the axial-radial plane). Furthennore, in addition to a complete visual and magnetic particle inspection of all bore and external surfaces, all modern nuclear wheel forgings are subjected to a s'.ringent 100% volumetric ultrasonic inspection at the time of manufacture. All nuclear wheels are soin tested during manufacture at 20% overspeed(although on some.early units a few whesis withou buckets attached), wnich further minimizes the probability of having'an undetected crack or crack-like flaw with a fritical size which would lead to spontaneous propagation at norwal rotating speeds. Thus, the major source of concern with respect to the in-service initiation and grcwth of cracks is that associated with stress corrosion. Al though we have i not observed stress corrosion.(or other) cracking in the bores of any of our fossil or nuclear wheels made of modern materials, the possibility of initiation i and propagation of a stress corrosion crack at the bore of a shrunk-on wheel cannot be entirely discounted. We and other turbine manufacturers have experienced stress corrcsion cracks in the wheel dovetail region of integral rotors made of essentially the same material as that used in nuclear LP wheels.

Recently, stress corrosion cracks were detected on the periphery of two modern GE shrunk-on wneels, operating in a fossil plant, wnich had been exposed to heavy caustic deposits.

In addition, machines of both domestic and foreign design (not GE) have suffered cracks in the bore region of shrunk-on wneels, leading to wneel bursts in several cas es. A considerable numcer of steps have been taken to reduce the probability of a wneel burst cue to stress corrosion cracking. Lacoratory tests and service experience have indicated that censistent hign levels of steam purity crovides the best protection against stress corrosion cracking. Steam purity recorrencations nave been published in GEX-72281, attacned. Modern wnaels manufactured for nuclear

2-f and fossil turtines are made from the highest quality vacuum poured NiCrd! forgings i which am heat treated to obtain an optimum combination of strength, ductility I and toughness. Each forging must pass a stringent material acceptance pmcedum before being considered for use as a wheel. The procedure includes the non-destructive inspections previously discussed, along with laboratory tests to ver'ify ) that material properties fall within specifications. Wheel geometries have been I chosen to maintain the lowest level of operating stress. Althougn a consid2rable effort has been made to maintain superior fracture toughness properties, and to minimize the likelihood for stress corrosion cracking, laboratory and field experiences indicate that the possibility for a wheel burst due to stress correston cracking cannot be discounted. For modern GE design nuclear shrunk-on wheels, the material crack size in the rim region whien would lead to a wheel burst is very large, approaching the axial thickness of the wheels. Thus, such cracks, should they exist, would have a high p*obability of detection by surface inspections. This is not the case in the bore region where, because of higher stress levels, a crack could grew to a dangerous size prior to breaking througn to an accessible surface. For this reason, G.E. has developed an ultra-sonic test which searches for cracks at the wheel bore and keyway surfaces, along with material in the vicinity of the bore. TIL-857, which was issued in February,1978, outlines our recomendations for periodic inspection of General Electric steam turbine rotors operating in nuclear power plants. As described in TIL-857, we recomend that a conclete magnetic particle inspection of the shrunk-on wheels should be performed during any outage when the turbine section is open. In addition, we reconnend a more extensive test at about 6 year intervals, which should include an ultrasonic inspection of the shrunk-on wheels usi'ng the wheel bore ultrasonic test mentioned above. A great amount of development work on stress corrosion cracking has been conducted, and our understanding of this phenorrenon is much improved, although still inadequate to predict the precise time required for crack initiation and the rate of crack growth in a cormsive environment. It is therefore imoossible to specify absolute " safe" inspection intervals to preclude tne possibility of initiating and growing a' crack to critical size between inspections. Recogni:ing this, w nevertheless believe that periodic inspections, as described in TIL-857, will greatly reduce the probability of a wheel burst. The remainder of this report describes in greater detail the service exoerience of G.E. wheek in nuclear and fossil plants, along with the steos whien nave Deen taken to unde:.cand and reduce the chances for a wneel burst. Also included is a description of the wheel bore ultrasonic test, and the experimental program which helped to develop and verify the test capabilities. SERVICE EXPERIENCE At the present time, 42 (35 domestic) large steam tureine-cenerator uni.ts manufacture by G.E. are coerating in nuclJar power plants. The 1579 shrunk-on wneels in these units nave accumulated over 9,000 wneel years of service without having experiencM & f ailum. To date 46 of these wneels have received an in-service wneel bore ultrasonic inspection with the result that no crack like indications ~ have been found.

3 Of the large steam turbine generators operating in fossil plants, 235 G.E. units nave shrunk-on wheels. This accounts for over 4000 wheels which have accumulated over 130,000 wheel years of service. To date, only one wheel failure has been experienced, and this ogcurred on a multiple stage Curtis design wheel which was made from an 1850 F austentized CrMoV material. The wheel had been in-service for roughly 30 years and was scheduled for replacement *. Metallurgical analysis of the fracture showed that cracks, probably caused by creep-rupture, initiated in pin bushing holes which extend radially from the bore surface. Unlike nuclear shrunk-on wheels which are used strictly in icw temgerature applications, this wheel operated at temperatures on the order of 900 F. The wheel fragments did not penetrate the turbine casing. Fourteen shrunk-on wheels from two GE units, not manufactured fmm a modern i NiCrMcV material, experienced stress corrosion cracking early in the 1950's. The cracks, which initiated in pin bushing (Nuclear wheels do not have pin holes, were detected within several years after the units went into service. holes.) An investigation revealed that a heavy build-up of deposits had formed on the turbine as a result of a large percentage of make-up water. To remove these deposits, the customer washed the turbine with a mild caustic solution. Caustic leaked into the pin holes, and concentrated during continued operation-resulting in the fornation of stress corrosion cracks. The wheels were replaced and the units placed back into service. Since this time, a total of 260 fossil wheels from 19 G.E. large steam turbines have received a full inspection. 166 of sich were disassemoled frem the shafts while 94 have been inspected with the wheel bore ultrasonic test. Wheel disassembly was largely perfonned in conjunction with TIL-647, which called for unstacking particular built-up rotors to improve shaft and wheel gecmetry. While unstacked, the wheels were given a complete magnetic particle inspection of bore and peripheral surfaces. No cracks were found in these wheel:. The wheel bore ultrasonic inspections performed to date on fossil wheels, resulted either from custcmer requests or from G.E. recommendations as the result of kncwn steam chemistry upsets. No crack-like indications have been detected in bore or keyway regions. Recently, a magnetic particle examination revealed stress corrosion cracks on the periphery of twe wheels operating in a fossil unit. This unit was found to have heavy deposits throughout., the chemical analysis of which revealed that they were largely formed by caustic deposition. Stress corrosion cracks were l found on the wheels and at other locations in the high pressure and Icw pressure I sections. Cracks on the wheel peripheries were found to be shallow. The ultrasonic inspection of the wheel bores and keyways revealed no indications, inelying that if cracks existed, they were shallow. l Experience of other manufacturers with wheel stress corrosion cracking in nuclear units has received considerable attention in recent years. Pe rtiaos the best documented is the British exoerience at the Hinkley Point A nuclear I power station. In Septemeer,1969, tureine generator No. 5 suffered a I catastrophic wheel burst, which studies found to be the result of stress corrosion cracks reaching a critical size in the wheel keywayd. A detailed follow-up study by the CEGB revealed stress corrosion cracks in a considerable numcer of wheels having semi-circular keyways. The 3 CrMov material used in many of these wheels was found to be temper embrittled and hignly susceptible to striss corrosion cracking.

4~ Bursts of large steam turbine wheels manufactured by other suppliers and operating in the United States are known to have occurred in fossil plants. Recent investigations have also revealed stress corrosion cracking in some nuclear steam turbine wheels. LABORATORY PROGRAM An extensive laboratory program has been undemay to better quantify the resistance of wheel materials to stress corrosion cracking. The program has concentrated on relating mechanical, material and electrechemical parameters to the pmcasses of crack initiation and growth. Most of the work to date has focused on caustic cracking, although other environments have been studied, including hign purity water. Caustic appears to represent the greatest threat to G.E. wheels operating in nuclear and fossil power plants. A considerable number of testing procedures have been utilized to investigate the rusistance of NiCrMcV steels to stress corrosion cracking. Figure I shcws results from dead weight load tests performed in caustic solutions under various conditions. Figure 2 illustrates the test apparatus with the environmental container removed so the smooth tensile type specimens can be observed. Scanning electron micrographs of a wheel material tested to failure in caustic are shown in Figure 3. Quantative measurements of the stress corrosion crack prcpagation rate in wneel alloys have been made using fracture mechanics type specimens (Figure 4). Generally, striss corrosion crack growth rates are depicted by plots of the type shown in Figure 5. The crack propagation rate is plotted versus the crack tip stress intensity factor, which is a function of the applied stress, the crack size and the geometry. A family of such curves are necessary to describe the variation of crack propagation rate with corrosion potential, temperature and caustic concentration. Of particular interest are the threshold stress intensity (Q), the plateau The threshdTd stress intensity or second stage, and the third stage of crack growth. is the limit below which stress corrosion cracks will not propagate. The plateau or second stage is the region of mlatively stable crack growth, over a range of stress intensity. Crack growth in regicn 3 is sharply accelerated as the crack tip stress intensity increases. Testing in the laboratory under controlled conditions has indicated that the threshold stress intensity in caustic is Icw, and in fact may be virtually non-existent. Figure 6 shows the typical range of stage 2 crack propagation rates versus tamperature measured on wneel materials in 40% NaOH and maintained near the optimum cormsion potential to accelerate crack growth. Corrosion potential has been found to be one of the most imocrtant parameters influencing the resistance of NiCrMcV wheel materials to caustic stress corrosion cracking. In the laboratory, corrosion potential can be e.ontrolled, thus providing a convenient means to run accelerated stress corrosion tests. Varying the potential from optimum, however, signficiantly reduces stress corrosion susceptibility. When uncontrolled, the fre'e corrosion potential in caustic generally lies outside the range of maximum severi ty, except under transient conditions. Addi*ional electrochemical studies have shown newever that trace quantities of certain concounds, sucn as PbO, Cc0 and NANO,, can influence the corrosion potential. It is possible tnat a critical Quantit'J of trace c:rrcouncs, if present in caustic deposits, will shift the potential towa cs an uncesirable

regioc. Thus, this is a possible mechanism for explaining why fos,sil_ steam - turbines, with caustic deposits,have not in all cases experienced stress corrosion cracking. Tests have been performed to evaluate the potential for stress corrosion crack propagation in high purity water. Such an environment is reasonably' j typical of condensate in the wet stages of steam turbines operating in plants with BWR reactors. The tests have shown that although stress corrosion cracks can i l pecpagate in this environment, maximum rates of propagation have generally been lower, by a factor of 100 to 1000, then the maximum rates in 40% caustic. Similar results have been published by the British, who tested NiCrMcV materials both in water and"high quality" power plant steam. GENERAL CONCLUSIONS Based on laboratory test results and service experience, some general conclusions have been reached with regard to the potential for stress corrusion cracking in shrunk-on v. heels. 1. Concentrated deposits, such as caustic, represent a significant threat to steam turbine components because of the possibility of developing stress corrosion cracks. The likelihood of cracks caused by caustic deposition is dependent on the corrosion potential, the temperature, the caustic concentration, the operating stress level, and the materials, and physical characteristics. Corrosion potential can be influenced by the presence of trace inpurity compounds. 2. Stress corrosion resistance generally decreases as the material tensile strength increases. 3. There is considerable heat to heat scatter in resistance to stress corrosion cracking within a given material specification. 4 Modern large steam turbines require materials which cannot be made complStely ininune to stress corrosion cracking. proper control Of water chemistry remains the best way to guard against stress corrosion cracking. 5. Some stress corrosion cracking has been observed in NiCrMoV laborator/ specimens exposed to pure water and wet steam environments. Maximum crack I growth rates measured in these environments however,are significantly less than those measured in more corrosive environments such as caustic, To date, G.E. ser41ce experience on steam turbine components manufactured t l from materials typical of modern wheel alloys has never linked stress corrosion cracking to pure steam or pure steam condensate. In all cases, stress corrosion cracks in these materials have been associated with l concentrated U"stic deposits. We believe.however,that at higher tensile strengths ard., at stress levels beyond those currently found in G.E. wneels. a significantly greater potential for stress corrosion cracking in relatively non-aggressive environments coes exist. 6. Locally aggressive environments may develop in surf ace pits or in regions of the tureine where steam flow is restricted. Wheel keyways are regions wnere this can potentially occur. i 7. In a contaminated steam environment cracks can grow by a stress corrosion mecnanism, to critical size. l.

l STEAM PURITY The need for good control of water chemistry in nuclear, as well as fossil ~ fired steam turbine power plants, is generally recognized and the concentration of impurities in such systens is generally held to very low levels. Due to effective concentrating mechanisms operative in steam turbines. low levels of impurities can be transformed into concentrated solutions, however. There are three major concentrating mechanisms operative in a turbine, and they are briefly described below. Some of these mechanisms may be operative to a greater extent in PWR plants than in BWR plants. 1. Deposition from Superheated Steam As steam expands through the turbine, the solubility of impurities i l in the steam decreases. Deposits form in the turbine when the concentration of impurities exceeds their solubility limit. The impurity concentration in a deposit can be far greater than its concentration in the steam. Concentrated caustic and chloride solutions are typical of deposits which can fann by deposition from superheated steam. Deposits of this type formupstream of the Wilson line. l 2. Acid Concentration at the Wilson Line Turbine steam may also be contaminated with organic or inorganic aci ds. Unlike the situation for caustic and chloride described above, acids are very soluble in superheated steam and do not exceed their l solubility. At the Wilson line, however, these acids become enriched in the first drops of water that are formed. This results in a situation in which low levels of acid in the steam can result in a concentrated acid solution at the early moisture region. 3. Evaporation and Orying Another concentrating mechanism which occurs in steam turbines is the formation of concentrating solutions by the evaporation of water from dilute solutions. Fer example, during a cold start-uo ste'am will condense on metallic surfaces which are at a lower temperature than the steam temperature. As the metallic part heats up, the moisture evaporates and practically all of the impurities are left. This concentrating I mechanism is not a significant problem for parts with exposed surfaces because ths imourities wil1 be redissolved by the large volume of steam I flow during operation. In stagnant areas, however, like the spaces between buckets and wheels br in the crevices between wheels and a shaft-) the solutions can concentrate and remain for long periods during operation. Some of the incidents that can result in contamination of nuclear turbines are: 1. Use of cleaning fluids with unacceptable levels of caustic, chloride and sulfur for removing protective materials used during shipment. 2. Cleaning solutions used to remove deposits frem the euroine or associated l components. l 3. Contaminated exhaust nood sprays used to control temperature in ene icw-pressure hocds during low lead operation.

~l' 4 Igroper operation and/or regeneration of feedwater demine'ralizers. 5. Contamination from condenser cooling water source because of condenser tube failures. Stress corrosion cracking has been found in fossil steam turbine components from each of these causes but not generally have shrunk on wheels been effected. GEX-72281 outlines General Electric steam purity recommendations as applicable to the turbine-generator unit. Other requirements may be applicable to maintenance of auxiliary components such as reactor components, steam piping, etc. WHEEL. OESIGN AND MATERI AL SELECTION Modern wheels manufactured by G.E. are made from vacutsn poured NiCrMov forgings which are heat treated to obtain the desired strength, ductility and toughness. The chemical composition and strength level of wheel forgings are chosen to best meet the service requirements of the wheel. To optimize stress corrosion resistance, tensile strengths are maintained at the lowest levels sufficient to adequately withstand operating stresses. Optimized material chemistry and processing results in wheel mateHals having superior toughness properties and thus superior resistance to brittle fracture. In the bore region of shrunk-on wheels, induced stresses pHncipally result from interference between the wheel and shaft, and the centMfugal forces of the buckets and wheel. Figure 7 shows the vaMation of tangential bore stress with rotational speed. The total stress, which is the sum of tM shrink and centrifugal stresses is reasonably constant up to the speed at which snrink is los:. Centrifugal stresses have been minimized in General Electric wheels by optimizing the wheel shapes and mounting only one row of buckets on each wheel. Reducing centrifugal stresses lowers the magnitude of shaft-to-wheel interference necessary to maintain shrink at nonnal operating speed. Thermal stresses induced by steady state and transient steam conditions are generally small in conparison with snrink and centrifugal stresses. In built-up rotors manufactured by G.E. and other manufacturers, shrunk-on wheels are keyed to the turbine shaft. This assures that even if shrink happens to be lost duMng transient operation, the wheels will not rotate relative to the shaft. Since keyways act as stress concentrators, local stresses in a wheel keyway are higher than nominal bort surface stresses. Tne magnitude of stress concentration is dependent on the size and shape of the keyway, which differs from manufacturer to manufacturer. ULTdASONIC TEST CESCRIPTICN j The wheel bore ultrasonic test searches for radial-axial cracks in the vicinity of the wheel. bore and keyway of shrunk-on wheels (Figure 8). Due to the conclex wheel geometry, every suitable wheel surface is used to ensure maximum inspection of the wheel bore and keyway. Tests are made from the wheel webs, hubs, and hub faces when accessible as snown in Figure 9,10, and 11. Twin pitch-catch 1 probes are used from tr.e wheel webs and faces and a single prebe technique is used i from the wneel hubs. Various beam angles are used to project the ultrasonic ::eam ) l l i

.g to the bort from the test surface in a way designed to detect racial exial defects. By varying the transducer positions in the manne of Figure 12 the axial length of the bore is tested. To obtain maximum coverage, each wheel may receive as many as forty individual scans with twenty in each opposing circumferential directio~n. On each scan, proper operation is monitored and sensitivity checks are made by measurement of the keyway signal amplitude. Figure 13 shows a block diagram of the standard test setup. The rotor is rotated slowly within the casing using either the turning gear or an auxiliary turning device. Automated manipulator ams, which are mounted on the horizontal l joint, position the transducers at precise locations and angles which have been pre-selected to provide the best assessment of each portion of the bore. If they j are available, the test can also be performed with the rotor set.up on power rolls. U1trasonic data is processed by the computer and graphically displayed for l operator review. Final results are stored on a magnetic disk for permanent retention. While developing this procedure, it was found that score marks which are sometimes pmduced on wheel bonesduring the rotor assembly may pmduce disproportionately large ultrasonic indication aaplitudes. A means of discriminating these signals from crack signals was obviously required. It was found that different test frtquencies produced a more proportionate response to flaw size. Consequently, a dual frequency technique was adopted as shown in Figure 14 O!TECTICN OF STRESS CORROSION CRACKS Stress corrosion cracks have historically proved difficult to detect with ultrasonic means. The tightly closed, intergranular cracks are filled with corrodent and corrmston products and usually exhibit poor reflectivity for ultra-sound. Although machined discontinuities were used in the early deveicoment of the test method, it was recognized that the was a need to establish the detectability on actual stress corrosion cracks cf the size being sought. An extensive program of producing stress corrosion cracks in full size wneels (Figure 15)and large ring specimens (Figure 16) was undertaken to verify the test :nethod. Stresses near yield were generated by shrinking the wheels on to a stub shaft which was heated to further create an additional source of stregs. The rings were stressed with a hydraulic jack. A 40% NaOH solution at 100 C was circulated through the wheel and ring keyways to produce stress corrosion cracks. The potential of the solution was controlled to accelerate corrosive attack. To date, a total of three wheels and two largs rings have been artifically cracked. The first wheel was exposed to 40% caustic for approximately one year and later broken open (Figure 17 and 18). Ultrasonic indication aplitudes equal to that of the keyway itself were observed from these cracks as shown in Figure 19 and 20. The deepest crack in this wheel was 1 1/4 inen (32 m). Numerous smaller cracks with accreximately 1/4" (6.4 m) deotn wert also present near tne axial end of the keyway and wrt detected from the wneel hub. Another wneel was exoosed with the objective of producing smaller cracks nearer to the detection limit of the ultrasonic test. After eight months of _ _ _ ~.. _. _ _ - - _.. _ _ _,

.g. exposure, ultrasonic tests of the wheel revealed significant cracking (Figure 21). A section containing the keyway was removed and magnetic particle tested (Figure 22) revealing an extensive network of cracks. Smaller cracks were successfully induced in two ring shaped specimens. Again, the uit 'tscnic techniques detected these cracks which ranged in depth to a maximum 0.18 inches (4.6 mm) with an average depth of 0.040 inches (1 mm). Figure 23 is a metallographic section showing some of the cracks. DISC'JESICN AND

SUMMARY

inrunk-on wheels manufactured by General Electric have established an excellent record of trouble free service. Efforts to minimize operating stresses and optimized material properties undoubtedly contribute to this record. However, laboratory tests and field experience have demonstrated that wheel materials, operating at stress levels found in shrunk-on wheels, could develop stress corrosion cracks in-service. Cracks which might initiate in the bore region could prcpagate and, if left undetected, could result in a wheel burst. It therefore 's prudent to inspect shrunk-on wheels periodically. General Electric has developed an ultrasonic test, which can be parformed with the wheels in place, and can inspect the critical bore and keyway regions. In February,1978, TIL-857 was issued reconunanding inspection practices for 1500 and 1800 RPM nuclear turbine rotors. It was, and still is recommended, that a wheel sonic inspection of nuclear shrunk-on wheels should be performed at about six year intervals. This, in conjunction with maintaining steam purity levels, as reccmmended in GEK-72281, will significantly reduc 3 the probability of a wheel burst. -,-------e- ,--,,e- - - ----,, ~ ~a -w

Reference 1. D. Kalderon, Steam Turbine Failme at Hinkley Point "A", Proc. Instn.- Mech. Engrs., Vol. 186 31/72, 1972. 2. J.L. Gray, Investigation Into the Consequences of the Failure of a Turbine-Ge.1erator at Hinkley Point "A" Power Station, Proc. Instn. Mecn. Engrs., Vol. 186 32/72, 1972. 3. T.G. McCord, B.W. Bussert, R.M. Curran, G.C.Gould, Stress Corrosion Cracking of Steam Turbine Materials, General Electric Report GER-2Ba3. I 1975. l 4. F. Aemirato, G.C. Wheeler, Ultrasonic Inspection of In-Service Shrunk-On Turbine Wheels, General Electric Report 79MPL405,1979. 5. B.W. Bussert, R.M. Curran, and G.C. Gould The Effect of Water Chemis ry on the Reliability of Modern Large Steam Turtines, General Electric Report GER-3086,1978 6. T. Cowgill and K.E. Robbins, Understanding the Observed Effects of. Erosion and Corrosion in Steam Turbines, Power Septemoer,1976. 7. R.M. Curran, B.R. Seguin, J.F. Quinlan, S. Toney, Stress Corrosion Cracking of Steam Turbine Materials, Southeastern Electric Exchange, Florida, April 21-22, 1969. (Proceedings wem not published and reprints are no longer available). i --r, ..---w--

SCC DATA LOAD VERSUS TIME TO FAILURE -~ 40% 212'F-960 mV (Vs. LAZARAN ELECTRODE) 28% 1504-960 mV (Vs. LAZARAN ELECTRODE) 28% 1804 UNCONTROLLED POTENTIAL 1 W!EK 1 MONTH 1 YEAR

2. YEARS I

I I \\ k o @O 00 o O 110 - \\ \\ 100 4 eG# GSG e o oo o o 00 Coco o - \\ \\ e G 900 l \\ v \\ \\ O = \\ o\\ 80 GSS 4889 GWee 80 - = e \\ \\ i E m \\ \\ S = .0 \\ \\ \\ \\ \\ .S. \\ 1 1 I 11 I I I I IIII I I I i 1111 1 100 1000 10.000 TIME TO FAILURE IN HOURS FIGURE 1: TIME TO FAILURE VERSUS APPUED STRESS FOR WHEEL MATERIALS IN CAUSTIC. THE SCUD UNE is THE LEAST SQUARES FIT TO THE 212*F,40% CAUSTIC DATA. THE DCTTED UNES ARE DRAWN PARALLEL TO THE SCUD UNE AND ROUGHLY THROUGH THE MEAN FOR THE OTHER TWO CONDmONS TO ILLUSTRATE THE EFFECT OF CHANGING CONDfTIONS ON TIME TO FAILURE.

_m r l g W' ' t. ar I 1 Y ?' w ~ ' I {..., ~ ' \\ i p g .m R i l ~~ t u. .) _ ~ =__ l ~~ i .3 d FIGURE 2 APPARATUS USED.FOR UNIAXIAL DEAD WEIGHT LOAD TESTING

l l i STRESS CORROSION FAILURE ,,.Ny .,.:,. v. 4, . Q,. ?~ .g r H T'g M 4. (a) 200X ,y,: ~ s. 4 s. ,Q # s (b) 500X k+V '? .. -.f- .p;s. ' \\ fg Figure 3: Scanning electron micrographs of fliCrt'oV sample. Micrograph (a) shows intergranul ar SCC near edge. Micrograph (b) shows transgranular tear at center of micrograph (a). j i

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t t CAACK GROWTH RATE IN CAUSTIC 10 1 2= Y I ENVIRONMENT: 40% NaOH j w V =.900 mV (Vs { K = 25-48 KSI u l g g g .01 150 175 200 225 250 i TEMPERATURE (*F) ) FIGURE 6: MEASURED STRESS CORACSION CRACX GROWTH RATE (Rf FOR NICrMoV WHEEL MATEMALS. CORROSION POTENTIAL MAANTAJ t

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GEK-46527A, PERIODIC OPERATIONAL TEST SU3!'.!ARY 1 l SUbG4ARY OF TESTS TO BE PERFORMED DAILY

SUMMARY

CF TEST MARY OF GON FONEG UNSUCCESSFUL TEST Fully close the main stop valves and comkned Shut down immediately by unloading and then valves by segaence teettag at the EHC Test tripping from the EHC panel. DO NOT OPEN Panet. the generator breaker unul ZERO or slightly NEGATIVE load has been reached. The cause of For details see " Flow Control" in Volume III. the problem should be corrected before restart-ing. !s all cases of malfunction, the operator must make his decisions with a thorough knowl. edge of the system and act in the best interests of safe operation and minimizing potential dam-age to the turbine (e.g. Water Induction may be a problein if an ope steam path exists to the arbine). Test for taovement of the extractica check Isolate the extraction line immediately. For de-valves provided with positive assist devices. tails, see " Extraction Check Valves", and in-restigste also per " Extraction Check Valves" in For details, see " Extraction Check Valves" Volume 1. In Vohame 1. Check the EHC fluid pump motor current. Follow procedure in section IV-D of " Hydraulic Power Unit for Electro-Hydraulic Control Sys-For details, see "Hydraelle Power Unit for tems" in Volume 1. Take pump out of " service Electro-Hydraulic Control Systems" la and investigate if required. Volume 1. Check the mechanical f111er condition indicators Change filter elements if any indicators or on the EHC hydraulic pump section strainers gauges show a change is required per section (and auxillary pump strainer when applicable) IV-C and IV-G of " Hydraulic Power Unit for and the pressare drop across the Fullers-Electro-Hydraulie Control Systems' in Vot-Earth filters in the EHC bydraalle system to u n e 1. ensure that all fliters are clean and insection-ing normally. For details, see " Hydraulic Power Unit for Electro Rydraulic Control Systems" la Vol-ume 1. 2

PER!CDIC OPERATIONAL TEST

SUMMARY

.CEK-46527A

SUMMARY

OF TESTS TO DE PERFORMED WEEKLY

SUMMARY

OF ACTION TO DE TAKEN

SUMMARY

OF 'I'ES'I. l ON AN UNSUCCESSFUL TEST Tully test ALL Main Turbine steam valves and Shut down immediately by unloading and tripping OBSERVE tne travel of the valve stems and from the EHC panet. DO NOT OPEN the gen-linkages locally. It is recognized on nuclear erator breaker until ZERO or slightly NEGATIVE fueled plants that it may not be practical to ap-load has been reached. The cause of the problem proach the valve during valve testing on a should be corrected before restarting. In all weekly basis due to the hlgh radiation level. cases of malhinction. the operator must make Nevertheless each valve should be observed his decisions with a thorough 'ctowledge of the from a safe distance o' ice a week, during valve system and act in the best interests of safe op-testing. to check for cha'iges la noise, vibra-eration and minimizing potential damrge to the tion and other behavior. turbine. (e.g.. water induction may be a prob-tem if an open steam path edsts to the turbine). For details see " Flow Control" in Volume m. Perform the Mechanical Overspeed trip test at Unicad the machine from the EHC par.el. Open the EHC Panel to test for operation of the Over-the generator breaker when ZERO or NEGATIVE speed trip device and Mechanical Trip Valve. toad has been reached then perform the checks outilned in " Trip and Monitoring" in Volume m For details, see " Trip and Monitoring" in before shutting down to correct the problem. Volume M. Perform the. Mechanical Trip Piston Test at Unioad the machine immediately (within one week the EHC panel to test for electrical activation if test en electrical trip is successfull from the , of the trip mechanism. EHC panel. Open the generator breaker when ZERO or slightly NEGATIVE Icad has been For details, see " Trip and Monitoring't in reached then perform the checks outlined in Volume M. " Trip and Monitoring" in Volume IU before shut-ting down to correct the problem. Perform the Electrical Trip Test at the EHC Unicad the machine immediately (*vithin one week panel to test for operation of the Electrical if test on mechanical trip piston is successful) l j a rtp Valve. from the EHC panel. Open the generator breaker when ZERO or slightly NEGATIVE load has been i l For details, see " Trip and Monitoring" in reached then perform the checks outlined in Volume 10. " Trip and Monitoring" in Voli.me !!! before shut-ting down to correct the pecbiem. Perform the " BACKUP OVERSPEED TRIP Co through the trouble shooting scheme in " Trip TEST" at the EHC panel to test the 2 out of 3 and Monitoring" in Volume m. Shut down should i logic ctreutts. only be accomplished after unicading at the EHC panel. The generator breaker should not be For details, see " Trip and Monitoring" in opened with any load on the machine ~ Volume IU. Cantinued on page 4 3

GEK 46527A. PERICDIC OPERATIONAL TEST SUMMArtY ~'

SUMMARY

OF TESTS TO BE PERFORMED WEEKLY (CONTINUED) I

SUMMARY

OF TEST

SUMMARY

CF ACTION TO BE TAKFN i ON AN UNSUCCESSFUL TEST t Perform the Power load unbalance test at the Reduce Icad to under 405 maximum unit load or EHC panel to check for correct operation, go into the standby mode before rentacing the power load unbalance board with the factory spare For details, see " Rate Sensitive lower load per " Rate Sonsttive power load unbalance analog unbalance analog and logic circuits ** La Vo!- and logic circuits" in Volume III. When in ume UI. Standby, load should be limited to 50% of maxi-mum unit load on units with trip anticipators and 80% of maximum load on units withcut trtp antict-pators. Individual units may have a higher per-missible load. Consult with your General Electric Representa!!ve for this load point. Test the Thrust Bearing Wear Detector for Investigate immediately and reset or repair sa!!sfactory trip points and operatirn, within one week. While the dettes is out of ser-Vice, avoid maximum load and switching in or For details, see " Thrust Bearing Wear Detec-out of feedwater heaters, tor Teeting" and " Thrust Bearing Wev Detec-For details, see " Thrust Bearing Wear Detector" tar" in Volume 1. l In Volume 1. I Test autsmatle starting of ALL motor driven Investigate and correct immediately malfunctions i pumps b) actuation of their pressure switches, of all DC motor drteen pumps. Investigate and l and excretse each standby pump. correct within one week malfunctions of all AC For details see " Automatic Pump Starting m e r Wu pumps. For p. m " Auto-Weekly" in ' Volume 1. matic Pump Starting Weekly'. Test for ala m annunciation on the oil tang Investigate immediately and repair within one level gauge, week. Check oillevel once per shift. Replenish m m al s as nmsean. FoNMs see .'. Oil Level Gauge Testing *. For details, see "Ot1 Level Gauge Testing" , yng,3, I I Check the air gap on the silver brushes in the Replace the stiver brushes and/or operate per l front standard for wear and west ral " Removable shaft grounding devtce" in Volume 1. l For details see " Removable shaft grounding device" in Volume 1. l Perform the EVA test if early valving is Replace with the factory spare per "Early valve p rovided, actuation analog and logic circuits" in Volume UI. t For details, see "Early Valve Actuation Analog , and logic circuits" in Volume III. Check that the air dryer on the hydraalic power Resctivate or change the desiccant immediately, unit has active deetccant. For details, see "Hydraulle Power Unit for , Electrohydraulle Control Systems" in Volume 1. i 4

IN-SERVICE INSPCCTICN OF 1500 & 1800 RPM NUCLEAR TURSINE ROTORS TIL-857 ~ datsd 2/17/78 PURPCSE The purpose of this technical information letter is to give recem-mandations for inspecting all 1500 and 1800 RPM nuclear turbine ro-tors and, in particular, to announce the availability of a newly de-veloped test for sonically inspecting shrunk-on turbine wheels. The mechanisms for initiating and/or growing cracks in nuclear shrunk-on wheels are also described, with particular reference to stress cor-resion and reccmmendations for steam purity. INTRODUCTICN Nearly all of the turbine-generators produced to date by the Large Steam Turbine-Generator Department for use with nuclear reactor cy-cles are tandem-compound units with a rotation speed of 1500 or 1800 RPM. These units are constructed with integral rotors (rotor mach-ined from a single forging), and/or built-up rotors. (shaf t with shrunk-en wheels and couplings). In most nuclear turbines the HP rotor is of integral construction and the icw pressure rotors are of built-up de-sign, although there were a few early exceptions to this general con-figuration. The recommended inspections to be conducted on nuclear turbine rotors, the available inspection techniques, and the recem-mended intervals for such inspections are described below. The Large Steam Turbine-Generator Department made plans several years ago to develop a means of inspecting the critical regions of shrunk-en nuclear turbine wheels without removing them from the turbine shaf t. This development is now complete. We now have available the capabili-ty of ultrasonically inspecting for cracks in the vicinity of the key-way and the bore of nuclear wheels with the wheels in place. These critical regions have previously been impossible to inspect without removing wheels, using available nondestructive tests. INTEGRAL ROTOR INSPECTION We recommend that nuclear integral rotors be given a thorough external inspection at each outage when the rotor is exposed. This inspection should include a ccmplete magnetic particle test of all external sur-faces, including retor, buckets, packings, journals, and couplings. Normal visual inspections should also be conducted at this time. We reccmmend a more ccmplate inspection of the rotor at apprpximately 10-year intervals. This should include magnetic particle and ultra-sonic inspections from the rotor periphery and frem the bore. A son-ic test of the wheel dovetails en each stage should also be perform-ed at this time. BUILT-UP RCTOR P!SPECTICN Ouring any cutage when a turbine secticn is open, the built-up retor should also be given a thorough inspection. This inspection should include a ecmplete magnetic particle test of all external surfaces, in-

In-Service Inspection of 1500 & 1800 RPM Nuclear Turbine Rotors (TIL 857) - Continued BUILT-UP ROTOR INSPECTION - Continued cluding shaf t, wheels, buckets, packings, journals, couplings, and' gears. Last stage erosion shields should be given a red dye inspec-tion, and all finger dovetail pins should be sonically inspected. We recommend a more extensive test at about 6-year intervals, includ-ing the ultrasonic inspection of tangential entry dovetails, and an l ultrasonic inspection of the shrunk-on wheels. The inaccessible wheel bore and keyway surfaces, and the material in the vicinity of the bore, should be inspected using the recently developed ultrasonic test described in the following paragraphs. The ultrasonic test of the bore and keyway regions must be conducted with the rotor being turned slowly at a constant speed. Specially designed ultrascnic transducers positioned on the hub and the web of the wheel are used to transmit ultrasound toward the bore. If a crack is present, a portion of the ultrasonic energy is reflected, ei-ther back to a dual transmitting / receiving crystal assembly, or to a receiver located at the appropriate location of the wheel. An analy-sis of the reflected signal is made to determine whether a crack is present. The material within 2 or 3 inches of the bore, including the keyway, is inspected by continuously varying the location of the transmitting and receiving crystals. Rotor turning can be accomplished in some cases with the turning gear. In other cases it may be necessary to make special provisions or modi-fications to achieve the required speed. The exact speed requirement and related reccarendations for the specific machine to be tested will be furnished prior to the outage. The turbine owner may wish to pur-chase a set of powered rolls. These could afford the added advantage of permitting the rotor to be tested away, from the turbine, so that other maintenance can be accomplished concurrently. The I&SE Service Engineer can provide the functional description of such rolls. The expected elapsed time for the wheel bore ultrasonic test is about five days for the first rotor and four days for each additional rotor inspection performed sequentially at the same site. This time does not include that required to prepare the wheels for the testing - cleaning the wheels, removing grease, rust, loose scale, etc., to per-mit close coupling between the ultrasonic transducers and the surf ace. The I&SE Service Engineer can discuss the required cleaning, and how it may be best accomplished. The internal portion of the wheel away from the bore, which is not in-spected during this test, is of much less concern. This is because a flaw of unacceptable size and location in the wheel, as manufactured, is unlikely. The manner in which the wheels are forged essentially precludes the possibility of producing an internal crack-like defect in the plane normal to the maximum stress (the axial-radial plane). Furthermore, all modern nuclear wheel forgings are sub3ected to a stringent 100% volumetric ultrasonic inspection at the time of manu- ,,-e v--

e In-Service Inspection of,,,, 1500 & 1800 RPM Nuclear Turbine Rotors (TIL 857) - Continued BUILT-UP ROTOR INSPECTION - Continued facture. All nuclear wheels are spin tested during manufacture at 20% overspeed, which further minimizes the probability of having an unde-tected crack or crack-like flaw with a critical size which would lead to spontaneous propagation at normal rotation speeds. Thus, the likeli-hood of a modern nuclear wheel entering service with an unacceptable defect is low. It therefore becomes more important to concentrate on the potential for the initiation and growth of cracks in service. There are two possible mechanisms for initiating and/or growing cracks in nuclear wheels in service: 1. Stress Cycling. 2. Stress Corrosion Cracking. The likelihood of initiating and/or growing a crack due to the stress cycling associated with etarts, stops, or load changes is small. The variation in ctress amplitude resulting from operating transients is too low to produce significant crack growth, in the unlikely event that a defect exists in the wheel when it is placed in service. Thus, the major source of concern with respect to the in-service initiation and growth of cracks is that associated with stress corrosion. Although we have not observed stress corrosion (or other) cracking in the bores of any of our fossil or nuclear wheels made of modern material, the pos-sibility of initiation and propagation of a stress corrosica crack at the bore of a shrunk-on wheel cannot be entirely discounted. We and other turbine manufacturers have experienced stress corrosion cracks in the wheel dovetail region of integral rotors made of essentially the same material as that used in nuclear LP wheels. For modern GE design nuclear shrunk-on wheels, the material crack size in the rim region l which would lead to wheel bursting is very large, approaching the axial thickness of the wheels. Thus, such cracks, shoulc. they exist, would have a high probability of detection by surf ace ins pections. This is not the case in the bore region where, because of higher stress levels, a crack could grow to a dangerous size prior to breaking through to an accessible surface. The ultrasonic test permits the inspection of this region of the wheel. A great amount of development work on stress corrosion cracking has been coaducted, and our understanding of this phenomenon is much im-proved, although still inadequate to predict the precise time required for crack initiation and the rate of crack growth in a corrosive en-vironment. Stress corrosien crack initiation and growth is a ecmplex process, in-l fluenced by many f actors such as material pro :erties, stress levels, en-l vironment,etc. and there is still considerabia uncertainty about their [ interaction. Data generated to date show a great deal of scatter on i

sat =gs 5 In-Service Inspection of -~ 1500 & 1800 RPM Nuclear Turbine Rotors (TIL 857) - Continued BUILT-UP RCTOR INSPECTION - Continued both crack initiation times and growth rates, so that it is impossible to specify absolutely " safe" inspection intervals to preclude the pos-sibility of initiating and growing a crack to critical size between in-spections. f Recognizing that periodic inspections at reasonable intervals cannot we nevertheless be-provide absolute protection against a wheel burst, l lieve that,such inspections will greatly reduce the probability of such Af ter having considered this and other *ictors, we con-occurrences. clude that inspection should be conducted at about 6-year intervals, as described above. The inspections can be coordinated with reactor refueling schedules and/ or sectionalized maintenance plans. TURBINE STEAM PURITY ~ We believe the control of steam purity is the most positive way of pro-tacting against stress corrosion cracking. Numerous studier have been made over the years to determine realistically achievable steam chemi-stry, and attempts have been made to relate impurity levels to the stress corrosion susceptibility of turbine materials. While much work remains to be done in this area, the attached instruction, GEK-63430, describes our judgment on the approach which we currently feel is workable and prudent. at present recommending a general inspection program for fos-We are not l sil turbine shrunk-on wheels. We may recommend occasionally that certain l wheels be inspected, depending cn specific circumstances. Requests for inspecting fossil wheels will be honored to the extent of our inspection capacity, but priority will be given to nuclear wheels. The information furnished in this technical information letter is offered In view of this by General Electric as a service to your organization. involves many factors not within our cnd since operation of your plant and since operation is within your control and responsibility, knowladge, it should be understcod that General Electric accepts no liability in negligence or otherwise as a result of your application of this inform-ation. -,m,, - - ,n-

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INSTRUCTIONS azx.22281 d e (New Enformation Augu t i979) i \\ l l 9 STEAM PURITY - STRESS CORROSION CRACKING i l I l }/' /'\\ \\ u\\ nb i 60\\'G f o These instructrorie do not purport to cover all deteels of verletions on eQuromt not to Drovrde for everY possobie contongency to be met in connectron wrtn installation. coeration or mountenance. Should further onformetron be deeored or snouldoneticuter prooiems serse wnien ore not covered suifierentry for the purcneser's puroonne. the metter should be referred to :he Generet Electric Company.

GEK.72281. STEAM PURITY - STRESS CORROSION CRACKING CONTENTS PAG 5 .3 G E N E R A L D ESCRIPTIO N................................................... .3 !!. O P ER ATION AL RECOMMEND ATIONS...................................... ............... 3 A. Once.Through Steam Supply Systems............................ .3 B. Drum Type Steam Supply Systems............... C. S team P un ty M o n ito nn s.................................................... 4 !!!. M AINTEN AN CE RECOMMEND ATIONS............................................ 5 ......5 A. Turb ine Deposi ts.................................................... 2 _, - - - _ _ _ _ _. _ _ _.. _. ~.. __

STEAM PURITY - STRESS CORROSION CRACKING. GEK 72281.... 1 l. GENER AL DESCRIPTION remam dissolved in the steam and pass into the turbme. For these systems, the Utilities have always controlled boder water water punty input to the boiler is a good chemistry to prevent corrosion and depoetta measure of the output steam punty. We m the boder, which can result tn tube fadures, conducted a water chemistry survey from and to prevent deposits in the turbine,which 1975 to 1977 in which quesconnaires and decrease unit output and lower ef5ciency, plant visits were used to assess current m. Sporadic instances of strees corroston cracking dustry practices related to feedwater treat-(SCC) in turbmes indicate that, m addition to ment, boder water chemistry and steam steps to prevent boder corrosion and turbme punty measurements. TI e survey results deposits, the water cheartstry must be con-

• rom 50 once through steam generators trolled to prevent the intruduction of corro-indicated that about 30% of the units con-save contaminants into the turbine which can tinuously menatoring sodium and cation cause SCC, conductivity of the final feedwater achieve typical values of :1 ppb or less sodium and The moet eenous correstve contaminants are 0.2 gmho/cm or less cation conductmty.

caustic, chlondes, and sulate (which decom-In those units reported to have been oper-posee into hydrogen, sulade). Due to power-ated withm these limits, no major stress ful concentrating mecharuams operative in correston cracking incidents have occurred turbines and the aggressive nature of corrosive and only a minor amount of pitting cor-contaminants in high concentrations, it is roston has been observed. necessary to restrict these contanunants to very low levels in the steam. The substitution In recognition that turbine operators need of hydrazine for sodium sulfite as an oxygen some margm on the feedwater chemistry scavenger has essentially elimmated problems limits to account for start ups, shutdowns, due to sulate. The elimination of chlondes and system upsets, we have adopted the and caustic is not as easy. Chlondes are almost following practical steam punty recom-always present in the condenser cooling water mandations which should provide adequate and condenser leaks permit chlonde to enter protection from senous SCC incide sts: the condensate stream. Caustic may be pre-sent intentionally

• rom chemical additions t It is recommended that: The steam punty the boder or unmtentionally from improper be mamtained at the lowest practicallevel operation and/or regeneration of condensate of contaminants not to exceed 3.0 pph Na pollehers or makea up domineralisers, and cotton conductivity of 0.2 umho/cm d"""# "#"# #E** U#"#' "" " " #

The steam punty required to prevent corro-ope n, /w snm pnds not umsng save deposats in utdity turbines is not pre-100 houn per inedent and mumukung sently known. However, correlanons between 500 houn u Iess M a 12 morith open:w Said service experience and utdity water nme. O pp6 M and 0.5 gmho/m should chemistry practices has enabled the General not be umded, sad duw mgency Electne Company to formulate steem punty e ndidons /w penode of 24 houn wiew guidelines that, if followed, are likely to avoid wM mumulation not ermdang 100 1 major SCC meidenta. These guidelines are houn in a f month pem W tm,200 desenbod in dotad below, ppb and catton conductivnty of 1.0 umhol em should not be exceeded. II. OPERATIONAL RECOMMENDATIONS

8. Drum Type Steem Supoly Systems A. Once Through Steerp Suppey Systems A major difference between drum type Minimia:ng the level of feedwater con-unita over once through desisne to the drum taminants is extremely important foswnce-boder's sodity to separate dissolved solida through type boders etnoe seaantially all from the steem due to the otrons affinity the impunties dissolved in the feedwater of the solids for the liquid phes.o.

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t GEK42281. STEAM PURITY - STRESS CORROSION CRACKING There is a much lower incidence of SCC C. Steam Purity Momtoring on units operated with drum type boilers. Since tbase boilera generally are not well Most of the senous instances of tur. matrumented, it is not poestble to niste bine corroelon damage for botn once. l this bett;r performance to steam purity. through and drum type boders are asso. cisted with accidents or upset condiuons. For example, in once-through systems. We would expect that drum boders oper. improper regenersuon of deep bed po. sted on the zero solids or all volatile tnac. lianers operated on the ammoma cycle can ment system would reeddy meet our mtroduce caustic mto the feedwater. In recommended limits on sodium and cation drum type systems, high drum levels, conducthnty listed abow for once.through foammg, or defecuve steam separator steam supply systems and these limsts baffles can significantly increase the should be adhered to. amount of carryover. Operation of any boder turbme system with severe conden-Some urum type boilers may be operated ser leaks can eventually introduce chlondes with a proctsion type control in which into the turbme. Avoiding such instances caustic is added to the boiler water to requires constant attention to condenser achieve the desired pH. Any carryowr leakage, demmeralizer effluent punty, and would result in the introduction of steam punty. caustic, a wry corroatve contaminant, mto the turbme. In order to minimize The measurement of steam punty in units corrosion damage to the turbme, drum operated with drum type boders is not as boders operated with precision control straightforward as for once-through types i should deliwr steam to the turbine that because of separation in the drum and the I meets the sodium and cation conductivity need for steam sampling. limits recommended above for once, through systems. Steam sampling techniques and instrumen. tation for drum boders should be user. to For drum type units operated with the provide assurance agamst the type of coordinated phosphate boder water treat. chemical upsets desenbed above. i ment, it is not evident what levels of sodium and cation conducuvtty are achiev. Saturated steam sampling at the drum may able m the steem. The lower incidence of be more readily accomplished than super. serious corrosion damage for such units heated steam sampitng. Although the sb. suggests that steam purity lewis are com. solute values of steam punty measure-parable to thoes found for once through ments can be inace.trate because of boders or that deposits containmg corro. nonnpresentative steam sampling, sucn i save contaminants are buffered by phoe. stea m punty momtormg is extremely phates. Si lum phosphates are not be. useful in detecung trends or step changes 11end to bs corroenn to turbme matenals. in the chemical carryover. It is posenble that the steam chemsstry limatations on units using coordinar=4 To prennt the meroduction of corrosive contammants into the turome we -ecom. phosphates do not need to be as strmgent as thoes recommended for once-through mend that sodium and cation conduct:vity systems and industry programs need to be be monitored. Controlling the sodium to established to determine appropriate limits low levels insures that the correstve com. for units unmg this type of treatment. For pounds sodium hydroxide and sodtum these reasons we are not spectfying steam chloride an controlled. I.4mitmg the ca. tion conductivtty le intended to provide purtty limits for drufn units uams coor. dinated phosphate but we do recommend a measure of protection agames some of momtering the steam purity, and careful the other potentially corrossve contams. nants. In the event that a reusole low level attention to feedwater control. 4

a o STEAM PURITY - STRESS CORRO810N CR ACKING, CEK.72281 chlonde analyzer suttable for power plant contammants have been introcueed mto use becomes available, we would strongly the unit. These deposit analyses provide recomrnend its use for steem punty the information required forlogicai recom. momtonng. mendations regarding the nondestructive exammation of entical turbme compo, nents and for formulating corrective ac. Ill. MAINTENANCE RECOMMENDATIONS tions to etuninate the source of con. taminants. A. Turtsne Deposits We would recommend ttiat turkme de. Dunng turbine inspections the unit posits be taken and analyzed dunng every should be careMiy inspected for de-inspection. The results should be reviewed poeta. Analyses of turbme deposits can with LSTG Engmeenng through Product provide an early warnmg that corrosive Service. e S

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s - - ~ ~ RE0 VEST FOR INFORMATION RELATED TO TURBINE DISCS SITE SPECIFIC GENERAL OUESTIONS - To Be Comoleted in 30 Days Provide the following information for each LP turbine: A. Turbine type B. Number of hours of operation for each LP turbine at time of last turbine inspection or if not inspected, postulated to turbine inspection C. Number of turbine trips an' overspeeds 0. For each disc: 1. type of material including material specifications 2. tensile properties data 3. toughness properties data including Fracture Appearance Transition Temperature and Charpy upper steel energy and temperature 4. keyway temperatures 5. critical crack size and basis for the calculation 6. calculated bore and keyway stress at operating design overspeed 7. calculated Kle data 8. minimum yield strength specified for each dise II. Provide details of the results of any completed inservice inspection of LP turbine rotors, including areas examined, since issuance of an operating license. For each indication detected, provide details of the location of the indication, its orientation, size, and postulated cause. Provide the nomina'l water chemistry conditions for each LP turbine and ~ III. describe any condenser inleakages or other significant changes in water chemistry to this point in its operating life. IV. If your plant has not been inspected, describe your proposed schedule and approach to ensure that turbine cracking does not exist in your turbins. V. If your plant has been inspected and plans to return or has returned to power with cracks or other defects, provide your proposed schedule for the next turbine insp2ction and the basis for this inspection schedule, including postulated defect growth rate. VI. Indicate whether an analysis and evaluation reqarillnq turbine missile. have been performed for your plant and provided to the sta f f. I f suc h.in analysis and evaluation has been performed and reported, please provide appropriate references to the available documentation. In the e vent that such studies have not been made, consideration should be given to scheduling such an action.

GI!;IF.IC OUESTIO:ts - To Be Comoleted in 30 Days Describe what quality control and inspection procedures are used for the disc bore and keyway areas. Provide details of the General Electric repair / replacement procedures II. for faulty discs. What immediate and icng term actions are being taken by General Electric III. What to minimize future " water cutting" problems with turbine discs? actions are being recommended to utilities to minimize " water cutting" Ofdi5457 Describe fabrication and heat treatment sequence for discs, including IV. thermal exposure during shrinking operations. / e}}