ML19316A832
| ML19316A832 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 05/16/1980 |
| From: | Ippolito T Office of Nuclear Reactor Regulation |
| To: | Parris H TENNESSEE VALLEY AUTHORITY |
| References | |
| IEIN-79-37, NUDOCS 8005270607 | |
| Download: ML19316A832 (3) | |
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- .. 6 n otou UNITED STATES 8Y #
NUCLEAR REGULATORY COMMISSION
.E WASHINGTON, D. C. 20555 May 16,1980
.,y Docket Hos. 50-259 50-260 and 50-296 Mr. Hugh G. Parris Manager of Power Tennessee Valley Authority 500A Chestnut Street, Tower II Chattanooga, Tennessee 37401
Dear Mr. Parris:
On December 28, 1979 the NRC Office of Inspection and Enforcement (IE) issued Information Notice No. 79-37 that discussed the discovery of Ordcks 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 on January 9,1980 to discuss the-probability of disc cracking in these turbines. A sumary 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.
Some indications in the keyway region have been reported in discs at three of these plants. General Electric personnel l
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 these indications and their effects on turbine disc integrity.
For this purpose we request that you provide the information sought in 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 turbine discs. We i
also recomend that if you have not already done so, that you develop a i
schedule for performing a full UT inspection of at least one of your low-pressure turbines during the next major outage of your plant.
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! r. Hugh G. Parris May 16,1980 This request for generic information was approved by GA0 under clearance number B-180225 (S79014); this clearance expires June 30, 1980.
Sincerely.
_ A Thomas A. Ippolito, Chief Operating Reactors Branch #2 Division of Licensing
Enclosures:
1.
Information Bulletin 79-37 2.
Meeting Summary 3.
Information Requests cc w/o enclosures:
See next page I
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i Mr. Hugh G. Parris May 16,1980 cc:
H. S. Sanger, Jr., Esquire General Counsel Tennessee Valley Authority 400 Commerce Avenue E 11B 33 C Knoxville, Tennessee 37902 Mr. Ron Rogers Tennessee Valley Authority 400 Chestnut Street, Tower II Chattanooga, Tennessee 37401 Mr. H. N. Culver 249A HBD 400 Commerce Avenue Tennessee Valley Authority
. Knoxville, Tennessee 37902 Robert F. Sullivan U. S. Nuclear Regulatory Commission i
P. O. Box 1863 Decatur, Alabama 35602 Athens Public Library South and Forrest Athens, Alabama 35611 i
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UNITED STATES ISINS NO.:
6870 NUCLEAR REGULATORY COMMISSION Accession No.:
OFFICE OF INSPECTION AND ENFORCEMENT 7910250525 VASHINGTON, D.C.
20555 December 28, 1979 IE Information Notice No. 79-37 CRACKING IN LOW PRESSURE TURBINE DISCS Description of Circumstances:
An anonymous letter was received by the Director of the Office of Inspection and Enforcement, on November 17, 1979 which alleged 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 rpm 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 examination) for crack detection have been developed and are being imple-mented in the field. The Office of Inspection and Enforcement was also notified on November 20, 1979 that during the current overhaul of Commonwealth Edison's Zion 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
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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 turbine 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 months of turbine operation.
The NRC staff is evaluating I
the turbine inspection results and analysis by Westinghouse.
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IE Information Notice No. 79-37 December 28, 1979 Page 2 of 2 Westinghouse also notified the staff that extrapolation of information obtained from Indian Point Unit 3 inspection and analysis indicates that disc cracking i
could be significant at Indian Point Unit 2 and the turbines should be inspected sooner than the spring outage of 1980.
The NRC staff is currently reviewing l
Consolidated Edison's plans for prompt evaluation of this poten".ial problem
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at this unit. lists the PWR plants having Westinghouse 1500/1300 rpm turbines.
The AA category represents those turbines which appear to have the earliest 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 de
'n.
Westinghouse has recommended the l
remaining machines of the Category sants be inspected as their service periods approach five years or in the event significant corrosion problems become evident during this time. The NRC staff is currently reviewing the need for inspection of those PWR plants having 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 account. Also, Westinghouse is currently re-evaluating their previously estimated 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 Notice is provided as an early notification of a possibly significant matter, the allegations and the generic safety implications of which are currently undergoing review by the NRC staff.
It is expected that recipients will review the information applicable to their facilities.
If NRC evaluations so indicate, further licensee actions may be requested or required.
Embedded
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cracking in keyways ~ nd disc bore areas have been observed only in Westinghouse a
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 the Director of the appropriate NRC Regicnal Office.
Enclosures:
As stated
CATEGORY AA UTILITY STATION UNIT Florida, P&L Turkey Point 3
Consolidated ED.
Indian Point 2
Pt NY 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
Consumers Pwr.
Palisades 1
Commonwealth Ed.
Zion 1 1
i Commonwealth Ed.
Zion 2 2
Florida P&L Turkey Point 4
Nebraska PPD Cooper 1
Wisc. Mich. Pwr.
" int Beach 2
Maine Yankee Bailey Point 1
Rochester G&E Ginna 1
Northern States Prairie Island 1
Wisc. P.S.
Kewaunee 1
1 4.
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p (Continued)
Page 2 of 3 CATEGORY A r
IJTILITY STATION UNIT Alabama Fower Farley 1
Alabama Power Farley 2
Baltimore G&L Calvert Cliffs 2
Carolina P&L Harris 1
Carolina P&L Harris 2
Carolina P&L Harris 3
4 Carolina P&L Harris 4
Cincinnati G&E Zimmer 1
l Comonwealth Ed.
Byron 1
Comonwealth Ed.
Byron 2
Comonwealth Ed.
Braidwood 1
Comonwealth Ed.
Braidwood 2
Connecticut Yankee Haddam Neck 1
Duke Power McGuire 1
Ouke Power McGuire 2
Duquesne Lt.
Shippingport 1
Ouquesne Lt.
Beaver Valley 1
Duquesne Lt.
Beaver Valley 2
Flordia Power Corp.
Crystal River 3
Flordia Power & Lt.
St. Lucie 1
Flordia Power & Lt.
St. Lucie 2
j Houston L&P So. Texas 1
Houston L&P So. Texas 2
Louisiana P&L Waterford 3
Metropolitan Ed.
Three Mile Island 2
i Northern States Pwr.
Prairie Island 2
Pub. Service E&G Salem 1
Pub. Service E&G Sales 2
Pacific G&E Diablo Canyon 1
Pacific G&E Diablo Canyon 2
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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 S
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o UTILITY STATION UNIT Duke Power Co.
Oconee 1
Duke 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 0.C. Cook 1
Indiana & Michigan Electric 0.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, part Paph 2, line 9: Change " inlet" to " outlet" Page 1, part - aph 3, lines 9 and 10: Change " Point Beach Unit 2" to
" Point Bea Ur.i t 1 "
Page 1, paragraph 3, line 10: After Point Beach Unit 1 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 "AN0" reclosure 1, line 8: Change to read:
" Yankee Atomic Electric, Yankee Rowe", lines 9 and 15: Change " Wise 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 4
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UNITED sTATL1 NLCLEAR REGULATORY COMMISSION
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FE3RUARY 2 1 2 5 MEMORAriDUM FOR:
A. Schwencer, Chief Operating Reactors Branch #1, 00R FROM:
W. J. Ross, Project Manager Operating Reactors Branch #1, 00R
SUBJECT:
MEETING WITH GENERAL ELECTRIC RELATED TO TURBINE DISC CRACKS At the staff's reqeast, 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-prmprietary and proprietary sessions is attached.
In the non-proprietary session General Electric's personnel discussed the following 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 pressure turbine wheels. This experience includes the operation of 35 turbines at nuclear generating plans (22 BWRs-of which only three have actually b.een inspected) and 4000 wheels at 235 fossil units (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 demineralizer, (experience with fossil plants has been good even with poor water chemistry).
General E'lectMc referenced a 1973 memorandum that postulated the proba-bilities of turbine missiles as folicws:
2.6x10j P (<127% normal turbine speed)
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1.5x10" P (runaway) 4.1x10~7
=
P (lifetime total)
=
P (annual average) 1.4x10-8
=
General Electric continues to reconinend 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 tests 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 120% operating speed.
- 4) Tolerance of defects caused by stress and corrosion maximized through choice of material.
- 5) Provision for UT testing of wheels after installation and use.
General Electric's personnel provided the following responses to questions from the audience.
1.
Retention of a 6-year interval for inspection of turbines was justified by operating experience and crack growth rate studies.
2.
Three G.E. turbines at nuclear plants (1 BWR 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 additional days l
would be needed to coglete the inspection of a recond rotor at the same site.
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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 under load and retain their protective capability during the test.
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Th.e G.E. representatives were not aware of any custceer
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experience where overspeed emergency systems have ever been used.
7.
Mininum 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.
Conparisons of stress corrosion cracking between turbine discs (3.5% M1 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 ficw chemicals (Westinghouse is considering such protection)
- 11. Thermal and vibrational stresses on turbine wheels are considered to be very small in comparision to design capability.
12.
G.E. does not presently have specific teams of inspectors mobilized for inspecting turbines.
- 7 William J. Ross, Project Manager Operating Reactors Branch #1 Division Of Operating Reactors Attachnents:
Attendees Slides used in G.E. presentation
ATTENDEES
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NRC R. 5. Coucnman W. JUcss D. P. Timo R. E. Johnson J. J. Hinchey M. L. Boyle W. J. Kaehler A. Taboada H. T. Watanase J. J. Zudans R. D. Brugge W. P. Gamill K. G. Hoge T. Ippolito W. J. Collins E. G. Arndt I. A. Peltier K. M. Cange F. Clemenson C. D. Seller M. Wohl R. W. Klecker K. R. Wichman W. S. Hazeiton V. Noonan
av g g;ge e -vin NAME UTILITY Paul Nastick Sechtel Power Corporation o
C. W. Hultman
- 'JP P S J. E. McEwen Portland General Electric John Coombe Stone and Webster Richard G. Kriftner American Electric Power Paul H. Barton Duke Power Corpany Craig F. Nierode Northern States Power Corpany Otakar Jonas Westinghouse James B. Lewis Consumers Power Company Robert L. Smith Yankee Atomic Electric Corgany Jim Knuber Jersey Central Power and Light Ccepany Larry A. Johnson Tennessee Valley Authority Norman H. Gaffin Philadelphia Electric Company Martin J. McCormich, Jr.
Philadelphia Electric Company L. Erik Titland Baltimore Gas and Electric Corpany Ronald O'Hara Baltimore Gas and Electric Corpany R. Niall M. Hunt Baltimore Gas and Electric Corpany R. G. Clisham Baltimore Gas and Electric Company S. F. f, nderup Omaha Public Power District C. C. Seitz Metropolitan Edison Company P. i. Colvert Commonwealth Edision Corpany R. J. Tamsii nga Commonwealth Edision Company W. G. Clark. J r.
Westinghouse R. E. Wa rner Westinghouse V. S. Anderson Westinghouse B. B. Seth Westinghouse J. F. Etzweiler American Electric Power i
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e NUCLEAR STEAM TURBINE WHEEL RELIABILITY e
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INTRODUCTION This paper deals with shrunk-on bucket wheels used in steam turbines
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manufactured by the Large Steam Turbine-Generator Department 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 recomendations, the use of optimum design, material ' selection and acceptance practices, and the introduction of a computerized in-service wheel bore ultrasonic test.
In February,1978.
TIL-857 was issued outlining recomended in-service inspection practices for nuclear steam turbine rotors manufactured by General Electric.
Recomendations include a conplete ultrasonic examination of the shrunk-on wheel bores at about 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 growing 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 possibility of producing an internal crack-like defect in the plane normal to the maximum stress (the axial-radial plane). Fi rthermore, 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 stringent 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 whee".s withou buckets attached), which further minimizes the probability of having an IJndetectec crack or crack-like flaw with a &itical size which woiild lead to spontaneous propagation at. normal rotating speeds.
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 materials, the possibility of initiation 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 corrosion 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 went detected on the periphery of two modern GE shnJnk-on wheels, operating in a fossil plant, which had been exposed to heavy caustic deposits.
In addition, machines.of both domestic and foreign design (not GE) have suffered j
cracks in the bore region of shrunk-on wheels, leading to wheel bursts in several cases.
A considerable number of steps have been taken to reduce the probability of a wheel burst due to stress corrosion cracking. Laboratory tests and service experience have indicated that consistent high levels of steam purity provides the best protection against stress corrosion cracking. Steam purity recomendations have been published in GEK-72281, attached. Modern wheels man' tctured for nuclear
. i and fossil turbines are made from the highest quality vacuum poured NiCrMoV forgings which are heat treated to obtain an optimum combination of strength, ductility and toughness. Each forging must pass a stringent material acceptance procedure before being considered for use as a wheel. The procedure includes the non-destructive inspections previously discussed, along with laboratory tests to verify that material properties fall within specifications. Wheel geonetries have been chosen to maintain the lowest level of operating stress.
Although a considerable 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 corrosion cracking cannot be discounted. For modern GE design nuclear shrunk-on wheels, the material crack size in the rim region which would lead to a wheel burst is very larga, approaching the axial thickness of the wheels.
Thus, such cracks, should they exist, would have a high probability of detection by surface inspections. 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. 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 reconnendations for periodic inspection of General Electric steEn turbine rotors operating in nuclear power plants. As described in TIL-857, we recommend that a complete ragnetic particle inspection of the shrunk-on wheels should be performed during any outage when the turbine section is open. In addition, we recommend a more extensive test at about 6 year intervals, which should include an ultrasonic inspection of the shrunk-on wheels using 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 phenomenon is much improved, although still inadequate to predict the precise time required for crack initiation and the rate of crack growth in a corrosive environment. It is therefore impossible to specify absolute " safe" inspection intervals to preclude the possibility of initiating and growing a' crack to critical size between inspections. Recognizing this, we 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 experience of G.E. wheels in nuclear and fossil plants, along with the steps which have been taken to understand and reduce the chances for a wheel 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 turbine-cenerator uni.ts manufacture by G.E. are operating in nuclear power plants. The 1579 shrunk-on wheels in these units have accumulated over 9,000 wheel years of service without having experienced a failure. To date, 46 of these wheels have received an in-service wheel bore ultrasonic inspection with the result that no crack like indications have been found.
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Of the large steam turbine generators operatirig in fossil plants, 235 G.E. units have shrunk-on wheels. This accounts for ever 4000 wheels which I
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 low tegerature 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 unit:, not manufactured from a modern NiCrMoV material, experienced stress corrosion cracking early in the 1950's.
The cracks, which initiated in pin bushing (Nuclear wheels do not have pin-b 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 formation 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 which were disassembled from the shafts while 94 have been inspected with the wheel bore ultrasonic test.
Wheel disassembly was largely performed in conjunction with TIL-647, which called for unstacking particular built-up rotors to improve shaft and wheel geometry.
While unstacked, the wheels were given a complete magnetic particle inspection of bore and peripheral surfaces. No cracks were found in these wheels. The wheel bore ultrasonic inspections performed to date on fossil wheels, resulted either from customer requests or from G.E. recommendations as the result of known 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 two 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. racks were found on the wheels and at other locations in the high pressure and low pressure sections. Cracks on the wheel peripheries were found to be shallow.
The ultrasonic inspection of the wheel bores and keyways revealed no indications, l
implying that if cracks existed, they were shallow.
Experience of other manufacturers with wheel stress corrosion cracking in nuclear units has received considerable attention in recent years. Pe rhaps the best documented is the British experience at the Hinkley Point A nuclear i
power station. In Septenter,1969, turbine generator No. 5 suffered a 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 number of wheels having semi-circular keyways. The 3 CrMoV material used in many of these wheels was found to be temper embrittled and highly susceptible to stress corrosion cracking.
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 underway to better quantify the resistance of wheel materials to stress corrosion cracking. The program has concentrated on relating mechanical, material and electrochemical parameters to the processes of crack initiation and growth. Most of the work to date has focused on caustic cracking, although other environments have been studied, including high purity water. Caustic appears to represent the greatest threat to G.E.
wheels operating in nuclear and fossil power plants.
3 A considerable number of testing procedures have been utilized to investigate the resistance of NiCrMoV steels to stress corrosion cracking. Figure 1 shows results from dead weight load tests perfonned in caustic solutions under various conditions. Figure 2 illustrates the tess 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 propagation rate in wheel alloys have been made using fracture mechanics type specimens (Figure 4).
Generally, stress 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 (K%), the plateau or second stage, and the third stage of crack growth. The threshdTd stress intensity is the limit below which stress cormsion cracks will not propagate. The plateau or second stage is the region of relatively stable crack growth, over a range of stress intensity. Crack growth in region 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 low, and in fact may be virtually non-existent.
Figum 6 shows the typical range of stage 2 crack propagation rates versus temperature measured on wheel materials in 40% NaOH and maintained near the optimum corrosion potential to accelerate crack growth.
Corrosion potential has been found to be one of the most important parameters influencing the resistance of NiCrMoV wheel materials to caustic stress corrosion cracking.
In the laboratory, corrosion potential can be controlled, 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 freie corrosion potential in caustic generally lies outside the range of maximum severity, except under transient conditions. Additional electrochemical studies have shown however that trace quantities of certain conpounds, such as pbO, Cu0 and NANO,, can influence the corrosion potential. It is possible that a critical quantity of trace compounds, if pmsent in caustic deposits, will thift the potential towards an undesirable
l 1 2 region. Thus, this is a pc3sible mechanism for explaining why. fossil _ steam turbines, with caustic deposits,have not in all cases experienced stress corrosion cracking.
Tests have been perfonned to evaluate the potential for stress corrosion crack propagation in high purity water. Such an environment is reasonably 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 propagate 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 corrosion cracking in shrunk-on wheels.
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 j
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.
I 4.
Modern large steam turbines require materials which cannot be made completely immune to stress corrosion cracking. proper control of water chemistry remains the best way to guard against i
5.
Some stress corrosion cracking has been observed in NiCrMcV laboratory specimens exposed to pure water and wet steam environments. Maximum crack growth rates measured in these environments,however,are significantly less l
than those measured in more corrosive anvironments such as caustic.
To date, G.E. service experience on steam turbine components manufactured 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 concentrated caustic deposits. We believe however,that at higher tensile strengths and/or at stress levels beyond those currently found in G.E. wheels, a significantly greater ootential for stress corrosion cracking in relatively non-aggressive environments does exist.
~
6.
Locally aggressive environments may develop in surface pits or in regions of the turbine where steam flow is restricted. Wheel keyways are regions where this can potentially occur.
l 7.
In a contaminated steam environment cracks can grow by a stress corrosion mechanism, to critical size.
O
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 oper6tive 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 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 ceposits which can form by deposition from superheated steam.
Deposits of this type formupstream of the Wilson line.
2.
Acid Concentration at the Wilson Line Turbine steam may also be contaminated with organic or inorganic acids. Unlike the situation for caustic and chloride described above, acids are very soluble in superheated steam and do not exceed their solubili ty. At the Wilson line, however, these acids becore 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 Drying Another concentrating mechanism which occurs in steam turbines is j
the fonnation of concentrating solutions by the evaporation of water j
from dilute solutions. For example, during a cold start-up ste'am i
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 mechanism is not a significant problem for parts with exposed surfaces i
because the impurities wil1 be redissolved by the large volume of steam flow during operation.
In stagnant areas, however, like the spaces between buckets and wheels br in the crevices between wheels a'nd 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 from the turbine or associated corponents.
3.
Contaminated exhaust hood sprays used to control temperature in the icw-pressure hoods during low load operation.
} 4 Igroper operation and/or regeneration of feedwater demineralizers.
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 DESIGN AND MATERIAL SELECTION Modem wheels manufactured by G.E. are made from vacuum poured NiCrMoV forgings which am 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 materials having superior toughness properties and thus superior resistance to brittle fracture.
In the bore region of shrunk-on wheels, induced stresses principally result from interference between the wheel and shaft, and the centrifugal forces of the buckets and wheel. Figure 7 shows the variation of tangential bore stress with rotational speed. The total stress, which is the sum of the shrink and centrifugal stresses is reasonably constant up to the speed at which shrink is lost.
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 stmsses lowrs the magnitude of shaft-to-wheel interference necessary to maintain shrink at nomal. operating speed. Themal stresses induced by steady state and transient steam conditions are generally small in cogarison with shrink 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 during transient operation, the wheels will not rotate relative l
to the shaft. Since keyways act as stress concentrators, local stresses in a wheel keyway are higher than nominal bore surface stresses. The magnitude of stress concentration is dependent on the size and shape of the keyway, which differs from manufacturer to manufacturer.
L'LTR' SONIC TEST DESCRIPTION A
The wheel bore ultrasonic test searches for radial-axial cracks in the vicinity of the wheel.bomand 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 shown in Figure 9,10, and 11. Twin pitch-caten probes are used from the wheel webs and faces and a single probe technique is used from the wheel hubs. Various beam angles are used to project the ultrasonic beam
t to the bore from the test surface in a way designed to detect radial axial defects.
By varying the transducer positions in the manner 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 direction.
On each scan, proper operation is monitored and sensitivity checks are made by measumment 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 joint, position the transducers at precise locations and angles which have been pre-selected to pmvide the best assessment of each portion of the bore.
If they are available, the test can also be perfomed with the rotor set.up on power rolls.
U1trasonic data is processed by the computer and graphically displayed for operator review. Final msults are stored on a magnetic disk for pemanent retention.
While developing this procedure, it was found that score marks which are sometimes produced on wheel boresduring the rotor assembly may pmduce disproportionately large ultrasonic indication anplitudes. A means of discriminating these signals from crack signals was obviously required.
It was found that different test frequencies produced a more proportionate response to flaw size.
Consequently, a dual frequency technique was adopted as shewn in Figure 14.
DETECTION 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 corrosion products and usually exhibit poor reflectivity for ultra-sound. Although machined discontinuities were used in the early development of the test method, it was recognized that there was a need to establish the detectability on actual stress corrosion cracks of the size being sought.
An extensive program of producing stress corrosion cracks in full size wheels (Figure 15)and large ring specimens (Figure 16) was undertaken to verify the test method. 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% Na0H 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 large 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 ang11tudes 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 inch (32 nin). Numerous smaller cracks with appmximately 1/4" (6.4 nun) depth wem also present near the axial end of the keyway and were detected from the wheel hub.
Anotha' wheel was exposed with the objective of prouucing smaller cracks nearer to the detection limit of the ultrasonic test. After eight months of
t
.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 ultrasonic techniques detected these cracks which ranged in depth to a maximum 0.18 inches (4.6 nn) with an average depth of 0.040 inches (1 mm).
Figure 23 is a metallographic section showing some of the cracks.
DISCUSSION AND
SUMMARY
Shrunk-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 propagate and, if left undetected, could result in a wheel burst.
It therefore is prudent to inspect shrunk-on wheels periodically.
General Electric has developed an ultrasonic test, which can be performed with the wheels in place, and can inspect the critical bore and keyway regions.
In February,1978, TIL-857 was issued recommending 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 recommended in GEK-72281, will significantly reduca the probability of a wheel burst.
I
Reference l
1.
D. Kalderen, Steam Turbine Failure 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-Generator at Hinkley Point "A" Power Station, Proc. Instn. Mech.
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-2883, 1975.
4.
F. Annirato, 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 Chemistry on the Reliability of Modern Large Steam Turbines 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, September,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 were not published and reprints are no longer available).
/
4
SCC DATA LOAD VERSUS TIME TO FAILURE 40%, 212*F 960 mV (Vs. LAZARAN ELECTRODE) 28%,150*F 960 mV (Vs. LAZARAN ELECTRODE) 28%.150*F UNCONTROLLED POTENTIAL 1 W!EK 1 MONTH 1 YEAR 2 YEARS I
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l
GEK-46527A, PERIODIC OPERATIONAL TEST
SUMMARY
SUMMARY
OF TESTS TO BE PERFORMED DAILY
SUMMARY
OF ACTION FOLLOWING
SUMMARY
OF TEST UNSUCCESSFUL TEST Fully close the main stop valves and combined Shut down immediately by unloading and then valves by sequence testir.g at the EHC Test tripping from the EHC panel. DO NOT OEN Panel.
the generator breaker until ZERO or sligatly NEGATIVE load has been reached. The cause of For details see " Flow Control" in Volume HI.
the problem should he corrected before restart-Ing. In all cases of malfunction, the operator must make his decisions with a thorough knoval-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 problem if an open steam path exists to the turbine).
Test for movement of the extraction check Isolate the extraction line immediately. For de-valves provided with positive assist devices.
tails, see " Extraction Check Valves", and in-vestigate also per " Extraction Check Valves" in For details, see " Extraction Check Valves" Volume 1.
In Volume 1.
Check the EHC fluid pump motor current.
Follow procedure in section IV-D of " Hydraulic Power Unit for Electro-Hydraulic Ccatrol Sys-For dotatis, see "Hydraulle Power Unit for tems" in Volume 1. Take pump out of' service Electro-Hydraulle Control Systems" in and investigate if required.
Volume 1.
Check the mechanical filter condition indicators Change illter elements if any indicators or on the EHC hydraulic pump suction strainers gauges show a change is required per section (and aux 111ary pump strainer when applicable)
IV-C and IV-G of " Hydraulic Power Unit for and the pressure drop across the Fullers-Electro-Hydraulic Control Systems", in Vo!-
i Earth filters in the EHC hydraulle system to ume 1.
ensure that all filters are clean and function-ing normally.
For details, see " Hydraulic Power Unit for t
Electro-HydranI!c Contral Systems" in Vol-t i
umel.
l
)
l 1
2 1
PERIODIC OPERATIONAL TEST SUM 3,tARY,GEK-46527A
SUMMARY
OF ?.STS TO DE PERFORMED WEEKLY
SUMMARY
OF ACTION TO BE TAKEN
SUMMARY
OF TEST 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 panel. 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 high radiation level.
cases of malfunction, the operator must make Nevertheless, each valve should be observed his decisions with a thorough knowledge of the from a safei distance once a week, durirg valve system and act in the best interests of safe op-testing, to check for changes in noise, vibra-eration and minimizing potential dam:ge to the tion and other behavior, turbine.
(e.g., water induction may be a prob-lem !! an open steam path exists to the turbine).
For details, see " Flow Control" in Volume HI.
i l
Perform the Mechanical Overspeed trip test at Uniond the machine from the EHC panel. 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.
load has beea reached then perform the checks outlined in " Trip and Monitoring" in Volume III For details, see " Trip and Monitoring" in before shutting down to correct the problem.
Volume HI.
Perform the. Mechanical Trip Piston Test at Unload the machine immediately (within one week the EHC panel to test for electrical activation if test on electrical trip is successful) from the
. of the trip mechanism.
EHC panel. Open the generator breaker when ZERO cr slightly NEGATIVE load has been For details, see " Trip and Monitoring" in reached then perform the checks outlined in Volume III.
" Trip and Monitoring" in Volume III before shut-ting down to correct the problem.
j l
1 Perform the Electrical Trip Test at the EHC Unload the machine immediately (within one week
)
panel to test for operation of the Electrical if test on mechanical trip piston is successful)
Trip Valve.
from the EHC panel. Open the generator breaker when ZERO or slightly NEGATIVE load has been i
For details, see " Trip and Monitoring" in reached then perform the checks outlined in
)
Volume III.
" Trip and Monitoring" In Volume III before shut-
)
ting down to correct the problem.
l l
Perform the " BACKUP OVERSPEED TRIP Go through the trouble shooting scheme in " Trip j
TEST" at the EHC panel to,teet the 2 out of 3 and Monitoring" in Volume III. Shut down should logic circuits.
only be accomplished after unloading 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 III.
Continued on page 4 3
GEK-46527A. PERIODIC OPERATIONAL TEST
SUMMARY
SUMMARY
OF TESTS TO BE PERFORMED WEEKLY (CONTINUED)
I
SUMMARY
OF TEST
SUMMARY
OF ACTION TO BE TAKEN l
CN AN tlNSUCCESSFUL TZST Perform the Power load unbalance test at the Reduce load to under 40% maximum unit load or EHC panel to check for correct operation.
go into the standby mode before replacing the power-load unbalance board with the factory spare For details, see " Rate Sensitive Power load per " Rate Sensitive pcwer load unbalance analog unbalance analog and logic circuits" in Vol-and logic circuits" in Volume UI. When in ume IH.
Standby, load should be limited to 50% of maxi-mum unit load on units with trip anticipators and 8
80% of maximum load on units without trip antici-pators. Individual units may have a higher per-missible load. Consult with your General Electric Representative for this load point.
Test the Thrust Bearing Wear Detector for Investigate immediately and reset or repair satisfactory trip points and operation, within one week. While the device is out of ser-vice, avoid maximum load and switching in or For details. see " Thrust Bearing Wear Detec-cut of feedwater heaters, tor Testing" and " Thrust Bearing Wear Detec-For details, see " Thrust Bearing Wear Detector" tor" in Volume 1.
l in Volume 1.
Test automatic starting of ALL motor driven l
Investigate and correct immediately malfunctions pumps by actuation of their pressure switches.
of all DC motor driven pumps. Investigate and and exercise each standby pump.
correct within one week malfunctions of all AC For details, see " Automatic Pump Starting m tor driven pumps. For details, see " Auto-Weekly'* in Volume 1.
matic Pump Starting Weekly'.
i Test for alarm annunciation on the oil tank Investigate immediately and repair within one level gauge, week. Check oil level once per shift. Replenish For details, see "O11 Level Gauge Testing" to normal Imis as nmssary. FoWaus see gy
.,011 Level Gauge Testing'.
Check the air gap on the silver brushes in the Replace the silver brushes and/or operate per front standard for wear and wear rate.
" Removable shaft grounding device" in Volume 1.
For details see " Removable shaft grounding device" in Volume 1.
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 M.
For details, see "Early Valve Actuation Analog and logic circuits" in Volume M.
Check that the air dryer on the hydranlic power Reactivate or change the desiccant immediately.
unit has active desiccant.
For details, see " Hydraulic Power Unit for Electrohydraulle Control Systems" in Volume 1.
4
IN-SERVICE INSPECTION OF 1500 & 1800 RPM NUCLEAR TURBINE ROTORS TIL-857 dated 2/17/78 PURPOSE The purpose of this technical information letter is to give recom-mendations for inspecting all 1500 and 1800 RPM nuclear turbine re-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.
INTRODUCTION 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 (shaft with shrunk-on wheels and couplings).
In most nuclear turbines the HP rotor is of integral construction and the low 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 recom-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-on 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 complete magnetic particle test of all external sur-faces, including rotor, buckets, packings, journals, and couplings.
Normal visual inspections should also be conducted at this time.
We recommend a more ccmplete inspection of the rotor at apprpximately 10-year intervals.
This should include magnetic particle and ultra-sonic inspections from the rotor periphery and from the bore.
A son-ic test of the wheel dovetails on each stage should also be perform-ed at this time.
i BUILT-UP ROTOR INSPECTION During any outage when a turbine section is open, the built-up rotor l
should also be given a thorough inspection.
This inspection should I
include a complete magnetic particle test of all external surfaces, in-
In-Service Inspection of 1500 & 1300 RPM Nuclear Turbine Rotors (TIL 857) - continued BUILT-UP ROTOR INSPECTION - Continued cluding shaft, 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 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 ultrasonic transducers positioned on the hub and the web of the wheel are used to tranutit 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 acccmplished 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 reccamendations 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 i
other maintenance can be accomplished concurrently.
The I&SE Service l
Engineer can provide the functional description of such rolls.
l The expected elapsed time for the wheel bora 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 surface.
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-l 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 subjected to a stringent 100% volumetric ultrasonic inspection at the time of manu-
- )
.~
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 therefere 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.
The likelihood of initiating and/or growing a crack due to the stress cycling associated with starts, stops, or load changes is small.
The variation in stress 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 bserved 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 which would lead to wheel bursting is very large, approaching the axial thickness of the wheels.
Thus, such cracks, should. they exist, would have a high probability of detection by surface inspections.
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 l
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 conducted, 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 corrosion crack initiation and growth is a complex process, in-fluenced by many factors such as material pro perties, stress levels, en-vironment,etc. and there is still considerabla uncertainty about their interaction.
Data generated to data show a great deal of scatter on
l l
i I
4 i
In-Service Inspection of 4
)j 1500 & 1800 RPM Nuclear Turbine Rotors (TIL 857) - Continued i,
I BUILT-UP ROTOR INSPECTION - Continued I
{
both crack initiaticn times and growth rates, so that it is impossible to specify absolutely " safe" inspection intervals to preclude the pos-i sibility of initiating and growing a crack to critical size between in-i spections.
f Recognizing that periodic inspections at reasonable intervals cannot provide absolute protection against a wheel burst, we nevertheless be-lieve that,such inspections will greatly reduce the probability of such occurrences.
After having considered this and other factors, we con-clude that inspection should be conducted at about 6-year intervals, as described above.
4 f
The inspections can be coordinated with reactor refueling schedules and/
or sectionalized maintenance plans, i
TURBINE STEAM PURITY
^
We believe the control of steam purity is the most positive way of pro-l tacting against stress corrosion cracking.
Numerous studies have been made over the years to determine realistically achievable steam chemi-stry, and atrempts have been made to relate impurity levels to the j
stress corrosion susceptibility of turbine materials.
While much work remains to be done in this area, the attached instruction, GEK-63430, l
describes our judgment on the approach which we currently feel is l
workable and prudent.
'l l
We are not at present recommending a general inspection program for fos-sil turbine shrunk-on wheels.
We may recommend occasionally that certain j
wheels be inspected, depending on specific circumstances.
Requests for i
inspecting fossil wheels will be honored to the extent of our inspection j
capacity, but priority will be given to nuclear wheels.
l 1
The information furnished in this technical information letter is offered l
by General Electric as a service to your organization.
In view of this i
and since operation of your plant involves many factors not within our l
knowledge, and since operation is within your control and responsibility, l
it should be understood that General Electric accepts no liability in negligence or otherwise as a result of your application of this inform-i ation.
' I" ~
11~IIJ INSTRUCTIONS czx.72281
'e i
.>;rd M I
h
.-(
i (New Information August 1979) l l
STEAM PURITY - STRESS CORROSION CRACKING I
c
\\J J
These instructione do not purport to cover all details or variations in equipment nor to provide for every postable contingency to be met in connection wrth installation, operation or meintenance. Should further informetion be densredor shouldparticularproblems anse which are not covered sufficientty for the purchaser's I
(
purposes, the matter should be referred to the Generet Electric Company.
d GEK.72281. STEAM PURITY - STRESS CORROSION CRACKING CONTENTS PAGE G EN E R A L D ES C RIPTIO N....................................................... 3 II. OPER ATIONAL RECOMMENDATIONS............................................ 3 A. Once.Through Steam Supply Systems............................................ 3 B. Drum Type Steam Supply Systems.........
.................... 3 C. S team Purity M onitoring...................................................... 4 111. M AINTENANCE RECOMMEND ATIONS........................................... 5 A. Turb ine Deposi ts............................................................ 5 9
O.
e
STEAM PURITY - STRESS CORROSION CRACKING. GEK 72251 1.
GENERAL OESCRIPTION remam dissolved in the steam and pass into the turbine. For these systems, the 1
Utilities have always controlled boiler water water purity input to the boiler is a good chemistry to prevent corroston and deposita measure of the output steam punty. We in the boder, which can result in tube failmes, conducted a water chemistry survey from and to prevent deposits in the turbine, which 1975 to 1977 in which quesucnnaires and decrease unit output and lower efficiency.
plant visits were used to assess current in-
)
Sporadic instances of stress corrosion cracking dustry practices related to feedwatertreat-(SCC) in turbines indicate that,in addition to ment. boder water chemistry and steam steps to prevent boiler corrosion and turbine punty measurements. The survey results deposits, the water chemistry must be con-from 50 once through steam generators
/
trolled to prevent the intruduction of corro.
indicated that about 80% of the units con-sive contaminants into the turbine which can tinuously monitoring sodium and cation cause SCC, conductivity of the final feedwater achieve typical values of 'l ppb or less sodium and The most serious corrosive contaminants are 0.2 umho/cm or less cation conductivity.
cauttic. chlorides, and sul5te (which decom-In those units reported to have been oper-poses into hydrogen. sul5de). Due to power.
ated within these limits, no major stress ful concentrating mechamams operative in corrosion cracking incidents have occurred turbines and the aggressive nature of corrosive and only a rninor amount of pitting cor-contaminants in high concentrations, it is rosion has been observed.
necessary to restrict these contammants to very low levels in the steam.The substitution In recognition that turbine operators need of hydrazine for sodium sulfite as an oxygen some margin on the feedwater chemistry scavenger has essentially eliminated problems limits to account for start ups, shutdowns, due to sulfite. The.*!imination of chlorides and system upsets, we have adopted the and caustic is not as cany. Chlorides are almost following practical steam punty recom-always present in the condenser cooling water mendations which should provide adequate and condenser leaks permit chlonde to enter protection from serious SCC incidents:
the condensate stream. Caustic may be pre-sent intentionally from chemical additions t It is recommended that: The steam purity the boder or unintentionall" from improper be maintained at the lowest practicallevel operation and/or regeneratio.s of condensate of contaminants nct to excend 3.0 ppb Na polishers or make up domineralisers, and cation conductivity of 0.2 umho/cm dunas a mdopmhons;dunngenomd The steam punty required to prevent corro-operation. for short periods not exceeding sive deposits in utility turbines is not pre-100 houn pe sneident cand acumulc Hng sently known. However, correlations between 500 houn w lue M ca 12 menth opmung Seld service experience and utility water Hme, O ppb.Vc and 0.5 umho/m should chemistry practices has enabled the General not be exmded: and dunns megency Electric Company to formulate steam punty
- "'I" ##"
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guidelines that, if followed, are Ilkely to avoid with auumulanon n t ermdsg 100 major SCC incidents. These guidelines are houn in a 12 month opmung Hme,10 0 described in detail below.
ppb and cation conductivity of 1.0 umhol cm should not be exceeded.
II. OPERATIONAL RECOMMENOATIONS
- 8. Orum Type Steam Supply Systems A. Once Through Stestp Supply Systerns A major difference between drum type Minimizing the level of feedwater con-units over once through designs is the drum taminants is extremely important for once-boiler's ability to separate dissolved solide through type boders since essentially all from the steam due to the strong affinity the linpurttles dissolved in the feedwater of the solids for the 11guld phes.o.
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GEK.72281. STEAM PURITY - STRESS CORROSION CRACKING There is a much lower incidence of SCC C. Steem Purity Monitoring on units operated with d3 type boilers.
Since these boilers generally are not well Most of the serious instances of tur.
instrumented, it is not possible to relate bine corrosion damage for both once-this better performance to steam purity, through and drum type boilers are asso-cisted with accidents or upset conditions.
For example, in once.through systems.
We would expect that drum boilers oper.
improper regeneration of deep bed po-ated on the zero solids or all volatile treet-lishers operated on the ammonia cycle can ment system would readily meet our introduce caustic into the feedwater. In recommended limits on sodium and cation drum type systems, high drum levels, conductivity listed above for once-through foaming, or defective steam separator steam supply systems and these limits baffles can significantly increase the should be adhered to.
a:nount of curryover. Operation of any botler turbine system with severe conden-Some drum type boilers may be operated ser leaks can eventually introduce chlandes with a precision type control in which into the turbine. Avoiding such instances caustic is added to the boler water to requires constant attention to condenser achieve the desired pH. Any carryover leakage, demineralizer effluent pur ty, and would result m the introduction of steam punty.
caustic, a very corrosive contaminant, into the turbine. In order to minimize The measurement of steam punty in units corrosion damage to the turbine, drum operated with drum type boilers is not as boilers operated with precision control straightforward as for once-through types should deliver steam to the turbine that because of separation in the drum and the meets the sodium and cation conductivity need for steam sampling.
limits recommended above for once-through systems.
Steam sampling techniques andinstrumen-tation for drum boilers should be used to For drum type units operated with the provide assurance against the type of coordinated phosphate boiler water treat-chemical upsets described above, ment, it is not evident what levels of sodium and cation conductivity are achiev.
Saturated steam sampling at the drum may able in the steam. The lower incidence of be more readily accomplished than super-serious corrosion damage for such units heated steam sampling. Although the ab-suggests that steam purity levels are com-solute values of steam punty measure-parable to those found for once through ments can be inaccurate because of boilers or that deposita containing corro-nonrepreecntative steam sampling, such sive contaminants are buffered by phoe-steam punty monitoring is extremely phates. Sodium phosphates are not be-useful in detecting trends or step changes lieved to be corrosive to turbine matenals.
in the chemical carryover.
It is possible that the steam chemistry limitations on units using coordinated To prevent the introduction of corrosive l
phosphates do not need to be as stringent contaminants into the turbine we recom-as those recommended for once-through mend that sodium and cation conductivity systems and industry programs need to be be monitored. Conuolling the sodium to established to determine appropnate limits low levels insures that the corrosive com-for units using this type of treatment. For pounds sodium hydroxide and sodium these reasons we are not specifying steam chloride are controlled. Limiting the ca-purity limits for drufn units using coor.
tion conductivtty is intended to provide dinated phosphate but we do recommend a measure of protection against some of monitoring the steam purity, and careful the other potentially corroalve contami-attention to feedwater control, nants. In the event that a reliable low level l
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STEAM PURITY - STRESS CORROSION CR ACKING GEK 72281 chlonde analyzer suitable for power plant contaminants have been introduced into use becomes available, we would strongly the unit. These deposit analyses provide recommend its use for steam purity the information required forlogicairecom-monitonng.
rr.endations regarding the nondestructive examination of critical turbine compo-nents and for formulating corrective ac.
Ill. MAINTENANCE RECOMMENDATIONS tions to eliminate the source of con-taminants.
A. Turbine Deposits We would recommend that turbine de.
Dunng turbine inspections the unit posits be taken and analyzed dunnt every should be carefully inspected for de.
inspection. The ~"Its should be reviewed posits. Analyses of turbine deposits can with LSTG Engineenng through Product provide an early warning that corrosive Service.
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G GENER AL $ ELECTRIC e
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809 t1Mi
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s CINERAL ELECTRIC - DGtESTIC IfUCLEAR TUR31NE=CENERATOR UNITS WITE C.E. BOILING WATER REACTORS OPERATING 08 UNDrR CCNSTRUCTION TUR31NE STAGES SERVICE CUS1MER STATICW/ UNIT RATING TTFE REREAT SATE Commonwealth Edison Dresden 1 210 TC2F-38 4/15/60 Jereer Central Power 6 Light Oyster Creek 1 641 TC6F 38 2
9/23/69 Niagare Mohaut Power Kina Mile Pt 1 620 TC6F-38 2
11/9/69 Comooveelth Edison Dresdes 2 810 TC6F-38 4/13/70 Northeast Utilities M111 stone Ft 1 650 TC4F-43 11/29/70 Northern States Power Monticello 1 543 TC4F-38 J/5/71 Comonwealth Edison Dresden 3 810 TC6F-38 7/22/71 Comosewealth Edisco Quad Cities 1 810 TC6F-38 4/12/72 Commonvestth Edieos Quad Cities 2 810 TC6F-38 5/23/72 lostos Edison F118tia 1 653 TC4F-43 7/19/72 Vernest Yankee 7t.Nuc. Power 1 537 TC4F-34 9/20/72 Tennessee Valley Authority Browne Ferry 1 1094 TC6F-43 10/15/73 Philadelphia Electric Feachbettas 2 1094 TC6F-43 2/16/74 love Electric Lisht 4 Power Arnold 1 See TC4F-38 2
5/19/74 Tennessee valley Authority Browne Ferry 2 1099 TC6F-43 8/28/74 Philadelphia Electric Feechbottos 3 1094 TC6F-43 9/1/74 Georgis Power Batch I 809 TC4F-43 2
11/11/74 FASNT Fitzpatrick 1 850 TC4F-43 2
2/1/75 Carolina Power & Light 3runswick 2 849 TC4F-43 2
4/29/75 Tennessee Valley Authority Browne Ferry 3 1091 TC6F-43 9/12/76 Caro 11aa Power & Light Brunswick 1 849 TC4F-43 2
12/4/76 Georgia Power Batch 2 817 E4F-43 2
9/22/78 Comecowealth Edison LaSalle 1 1147 TC6F-38 2
Shipped Pennsylvania Power & Light Susquehanna 2 1045 TC6F-38 Shipped Feeney1venta Power & Light Suequehanna 1 1085 TC6F-38 Shipped Commouvealth Edison LaSalle 2 1147 TC6F-38 2
Shipped Long !aland Lighting Shorehm 1 847 TC4F-43 2
Shipped Cleveland Electric 111minating Ferry 1 1253 TC6F-43 2
Shipped Illinois Power Clinton Power 1 985 TC4F-43 1
Shipped Niagers Mohawk Power Nine Mile Ft 2 1164 TC6F-38 g
Shipped Gulf States Utilities River Seed 1 998 TC4F-43 1
3hiFF'd Cleveland Electric illuminating Ferry 2 1233 TC6F 43 2
To be shipped Philadelphia Electric Limerick 1 1092 TC6F-38 Shipped Northern Indiana Public Service Baily Nuclear 1 684 TC4F-38 2
To be shipped Public Service Electric & Cae Hope Creek 1 1118 TC6F-38 Shipped Fuhlic Service Co. of Oklahoma Black Fox 1 1180 TC6F-43 To be shipped bl Stat es Utilities saver Send 2 998 TC4F-43 1
To be shipped
- ublic Service !!actric & Ces depe Creek 2 1113 TC6F-38 Shipped Public Service Co. of Oklahees Black Fox 2 1180 TC6F-4 3 To be shipped Philadelphia Elsettic Limerick 2 1092 TC6F-38 Shipped 111& note Power Clintos Power 2 985 TC4F-43 1
To be shipped 1
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o GENERAL ELECTRIC - DOMESTIC WUCLEAR TUR31NF-GENERATCR UNITS WI!M PRESSURIZED WATER REACTC85 CFERATING OR UM0ER CCNSTRUCTION
- t'R31NE STAGES REACTCR SERV!CE C STUMUt STATION / UNIT RATTNG TTFE REHEAT MFC NTE Weeniagton Public Power Basford Sta 2 422 TC4F-43 CE 4/18/66 Wiskieston Public Power Easford Sta 1 422 TC4F-43 GE 6/12/66 Dea Power Oconee 1 887 TC6F-38 2
SW 5/6/73 Onehe Public Power Dietrict Ft. Calhoua 1 481 TC4F-38 CE 8/25/73 Duke Power Ocasee 2 887 TC6F-38 2
BW 12/5/73 saltimore ces 6 Electric Calvert 1 890 TC6F-38 2
CE 3/6/74 Metropolitan Edison 3 Mile Isle 1 837 TC6F-38 BW 6/19/74 Duha Power Oconee 3 893 TC67-38 2
SW 9/18/74
!adiana Michtsaa Electric Cook 1 1G89 TC6F-43 1
W 2/10/75 NoIthesit Utilities Milletone Ft 2 881 TC4F-43 2
CE 11/9/73 F rtlaat General Electric Trojaa 1 1178 TC6F-38 W
12/22/75 Talado EJiaos Davie-leese 1 925 TC4F-43 2
BW 8/29/77 Arkanese Power 6 Light Arksaaes Nuc 2 943 TC4F-43 2
CE 12/26/78 South Caroline Electric 6 Gas Smr1 954 TC4F-43 1
W Shipped Consumere Power Midland 2 852 TC4F-43 2
BW Shipped Duke Power Catombe 1 1205 TC6F-43 2
V Shipped Publis Servise Co. of W.R.
Seatroek 1 1197 TC6F-43 1
W Shipped comeumere Power Midland 1 505 TC2F-43 2
tw Shipped UIton Electric Callauer 1 1192 TC6F-38 2
g Shipped Artsona Fnblic Service Pelo Verde 1 1359 TC6F-43 2
CE Shipped Ease:S Cao 6 Electric Wolf Creek 1 1192 TC6F-38 2
W Shipped Duke Power Cateute 2 1205 TC6F-43 2
w To be shipped GeorgLa Power Vogtle 1 1137 TC6F-38 1
g To be shipped Public Service Co. of 5.5.
Seabrook 2 1197 TC6F-43 1
W Shipped Arizona Public Service Falo Verde 2 1359 TC6F-43 2
CE to be shioned socnetter Gee e Electric Sterling auc 1192 TC6F-38 2
W To be shipped 7tledi Edsson Davis Resee 2 914 IC4F-43 2
By To be shipped Northern Statee Power 1
119%
TC6F-38 2
V To be shipped arisou h,elic Service Verde 3 1357 TC6F-e) 2 CE To be shipped Duka Power Cherokee 1 1341 TC6F-43 2
CE To be shipped Tennessee talley Authority Yellow Creek 1 1339 TC6F-43 2
CE To be shipped northeaet 'Jtilittes Milletone 3 1209 TC6F41 1
W Shipped Tee:eesee Valler Authority Yellow Creek 2 1339 TC6F-4) 2 CE To be shipped Catos Electric Callower 2 1192 TC6F-38 2
W To be shipped Tstado Ediace Devie Seese 3 914 TC4F-43 2
SW To be shipped Duka Power Cherokee 2 1341 TC6F-43 2
CE To be shipped Long Island Lighting Jamesport 1 119C TC6F-43 1
W to be shipped j
Coorgia Power Vogtle 2 1137 TC6F-38 1
V To be shipped 1
Duke Power Cherokee 3 1341 TC6F-43 2
CE To be shipped Long Island Lighting Jamesport 2 1196
.TC6F-43 1
W To be shipped l
1
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GE TURBINE OWNERS Branch 4
Arkansas 2 2
Big Rock Point 3
Brunswick 1&2 3
Browns Ferry 1,2,3 4
Calvert Cliffs 1 4
Davis Besse 1 3
Duane Arnold 2,3 Dresden 1,2,3 4
Fort Calhoun Fort St. Vrain 3
Fitzpatrick 3
Hatch 1&2 2,4 Millstone 1,2 3
Monticello 3
Nine Mile Point 1&2 4
Oconee 1,2,3 2
Oyster Creek 3
Peach Bottom 1&2 3
Pilgrim 1&2 3
Quad Cities 1
Trojan 4
4 Three Mile Island 1 3
Vermont Yankee 1
Cook 1 s
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Enclostre 3
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REQUEST FOR INFOR!'ATION RELATED TO TURBINE DISCS SITE SPECIFIC GENERAL OUESTIONS - To Be Comoleted it. 30 Days I.
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 and overspeeds D.
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 sin and basis for the calculation 6.
calculated bore and keyway stress at operating design overspeed 7.
calculated Kic data 8.
minimum yield strength specified for each disc 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.
III. Prov4de the nominIl water chemistry conditions for each LP turbine and 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 turbine.
V.
If your plant has been inspected and plans to return c,r has returned to power with cracks or other defects, provide your proposed schedule for the next turbine inspection and the basis for this inspection schedule, including postulated defect growth rate.
VI.
Indicate whether an analysis and evaluation reqardinq turbine missile.
have been performed for your plant and provided to the sta f f.
If such an analysis and evaluation has been performed and reported, please provide appropriate references to the available documentation.
In the event that such studies have not been made, consideration should be given to scheduling such an action.
' e GEt:ERIC OUESTi0t/S - To Be Comoleted in 30 Days I.
Describe what quality control and inspection procedures are u;Ed for the disc bore and keyway areas.
II.
Provide details of the General Electric repair / replacement procedures for faulty discs.
III. What immediate and long term actions are being taken by General Electric to minimize future " water cutting" problems with turbine discs? What actions are being recommended to utilities to minimize " water cutting" of discs?
IV.
Describe fabrication and heat treatment sequence for discs, including thermal exposure'during shrinking operations.
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