ML20084P909

Forwards Formal Rept Re Corrosion Found on Vessel Closure Studs,Stud Nuts,Washer & Holes & on Head & Vessel Flange Surfaces.Caused by Accumulation of Borated Water During Venting Operations

ML20084P909
Person / Time
Site:	Palisades, 05000000
Issue date:	12/20/1971
From:	Bacon J CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Jensch S, Nyer W, Williams C BROOKHAVEN NATIONAL LABORATORY, IDAHO NUCLEAR CORP., Atomic Safety and Licensing Board Panel
Shared Package
ML20084P711	List: ML20084P909
References
NUDOCS 8306130069
Download: ML20084P909 (2)

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December 20, 1971 sur..o. att e rs ,

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A. D. Dass C . D . On-son R . , . G od tro ut I ,' : ",',l", AFC DOCKET NO. 50-255 - PALISADES PUdC A . D. McCallunt W. R . MsHs 1 J . K. Restrick D. R. Hood J . M . S en.t h 4- t r, A. T. Udays

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Mr. Samuel W. Jensch, Chairman Dr. Clarke Williams Atomic Safety and Licensing Board Brookhaven National Laboratory U. 3. Atomic Energy Co.miusion Upton, L.I., New York 11973 Washington, D. C. 20545 Mr. Warren E. Nyer Idaho Nuclear Corporation P.O. Box 1845 Idaho Falls, Idaho 83401 Gentlemen:

In view of the AEC Regulatory Staff's December 10, 1971

/ letter to the Board, in which corrosion of the Palisades reactor vessel closure studs was mentioned, I an enclosing a copy of our formal report (required under the reportin6 requirements of Opera-ting License No. DPR-20) of the problem.

As the report states, corrosion was found on many of the studs, stud nuts, vashers and holes, and on the head and vessel flange surfaces. The corrosion was caused by an accumulation of borated water during venting operations conducted after filling the primary system. Venting equipmer', is being modified to pre-vent recurrence.

During nondestructive magnaglo testing, 20 of the 54 studs ~ ,

exhibited " linear indications." Staff counsel has mistakenly re-ferred to these indications as " cracking. " Metallurgical examination by Co:::bustion Engineering, Inc. in Chattanooga, Tennessee has verified that the indications were not defect indications, but rather indi-cations resulting from magnetic permeability variations probably C'

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Mr. Samuel W. Jensch, Chairran P.r. Warren E. Nyer Dr. Clarke Williams Decc=ber 20, 1971 caused by slight variations in surface cold work induced by machining and possibly intensified by heating incurred in phos-phate coating and in service. The metallurgical examination confirmed that the studs are fit for service.

Yours very truly,

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., e JLB:bbm [ Jupd L. Eacon CC: Myron M. Cherry, Esq.

Lewis D. Drain, Esq.

Parvin F. Metge, Esq.

Joseph S. Scinto, Esq.

George F. Trowbridge, Esq.

Mr. Stanley T. Robinson, Jr.

Curtis G. Beck, Esq.

Algic A. Wells, Esq.

Nathaniel H. Goodrich, Esq.

Eric V. Brown, Sr., Esq.

[  % Consumers Power (s.OyCompany

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\ . IQW d ff c.n.,a ome.s. 2i2 w u u.chsgan Avenue Jackson. Mich. gen 49201. Area Code 517 788-OSSO December 17, 1971 Dr. P. A. Morris, Director Re: Docket 50-255 Division Reactor Licensing License No DPR-20 United States Atomic Energy Commission Washington, DC 20545

Dear Dr. Morris:

The purpose of this letter is to formnlly report the difficulty experienced in removing the nuts from the reactor vessel studs at our Palisades Plant.

During the investigations of and repairs to the control rod drive mechanisms (reference our Special Report No 1 dated December 3, 1971), it was decided to remove the reactor vessel head in order to inspect the hanger sections of the control blades.

However, there were difficulties experienced in removing the nuts from the reactor vessel studs.

These difficulties were reported to the Division of Com-pliance representatives who subsequently reviewed and witnessed the inspection and rework program on these reactor vessel studs.

The cause of this problem, the results of subsequent in-vestigations and the nature of the rework of these studs follow.

The reactor vessel head removal process revealed that 41

! of the 54 reactor vessel stud nuts were frozen to the studs to the extent that they could not be removed using the stud tensioner. The stud tensioner has a very low mechanical advantage for turning the nuts. The studs and nuts were removed with the use of bolt heaters and a special slugging wrench under the supervision of Combustion Engineering, Inc personnel. The difficulty experienced in unbolting theheadwasattributedtocorrosionand/orcorrosionproductson the stud shank and threads. Corrosion products were also observed on the head flange stud holes, head flange surface, reactor flange surface, exterior of nuts and inner circle of the stud washer.

All studs were sent to the stud manufacturer for assessment of corrosion and rework. Two nuts acecmpanied the studs. These nuts u were selected as visual examples of the most corrosion. The corrosion on the studs was centered on the shank area and the first few threadsp nw ==s M&c" + e+A

O O 2 Dr. P. A. Morris December 17, 1971 adjoining the shank on each end of the chank. Approximately three (3) threads on the bottom (vessel end) of the shank showed heavy corrosion while approximately six (6) threads were affected on the top end of the stud. From visual appearance of the corroded threads, it was ob-vious that not more than one (1) to two (2) corroded threads were en-Saged in the nut or the vessel flange. The balance of the threads was unattacked. They exhibited a coating of lubricant with some heavy lubricant buildup in the th*ead roots. The lower end of the stud shank showed a corrosion band on all studs that was approximately 1-1/2" wide.

When lower end thread corrosion was added to shank corrosion, a band of approximately 1-3/4" was noted. This corrosion was fairly uniform over all studs. This band width corresponds to a countersunk area on the vessel flange.

Corrosion products were either a low-temperature aqueous red oxide believed to be aFe00H or a high-temperature hard gray deposit believed to be aFe203 . The stud chanks had general corrosion. In many cases, there was a streaming pattern indicating corrosion fres a vapor phase since the streaming patterns were from the bottom of the stud to the top. The two nuts that were sent were Ihr:bers 51 and 52.

They had a heavy deposit of salt (believed to be boric acid salt) on the exterior flats. Only minor corrosion was evident on the nut thread leads. There was corrosion on the inner circle of the washers, the vessel flange and the head flange. Stud holes in the head flange were

, corroded and showed evidence of streaming like that found on the stud

! shank. The threads in the vessel flange were only slightly affected l by the corrosion. Tbere was only minor corrosion to the thread lead and the bottom of the stud holes showed some slight evidence of cor-rosion products.

Rework procedures were d?veloped to refurbish the studs as follows:

I. Removal of Corrosion Products A. Machine heavily corroded areas on shank next to threads on both ends. Permission was received from CE, Chattanooga, to reduce the shank diameter by a maximum of 0.020" below present drawing limits. The stud manufacturer planned to remove 0.015" maximum.

B. Grind the corroded threads to clean them. Permission was re-ceived from CE, Chattanooga, to reduce the minor diameter by a maximum of 0.010".

C. Re=aining corrosion spots were to be hand polished.

D. Corrosion product cleanup and the stripping of the Parkerizing were to be completed by blasting with steel shot.

Dr. P. A. Morris 3 December 17, 1771 II. Nondestructive Testing The studs were to be magnetic-particle tested by the "magnaglo" method after shipping. Testing is done to ASTME-138-63 and CE Specifications.

III. Parkerizing A magnesium phosphate Parkerized coating is to be applied to the studs.

IV. Uut and Washer Work The only work required on the nuts and washers was removal of the corrosion products.

The rework has been completed and the studs returned to the Palisades Plant for reinstallation. During the nondestructive testing phase of the rework of the studs, 20 of the 54 studs exhibited several linear indications. All indications were in the shank portion of the studs and were in a circumferential orientation. Two of the studs showing these indications were shipped to Chattanooga, Tennessee, for metallurgical investigations to detemine the cause of these linear indications. A description of the metallurgical investigations con-ducted and their results are contained in Attachment I.

From the metallurgical investigations perfomed, it was verified conclusively that the circu=ferential "magnaglo" indica-tions on these studs were not defect indications. The sensitive "magnaglo" test revealed indications resulting frcm magnetic permeability variations probably caused by slight variations in surface cold work induced by machining and possibly intensified by heating incurred in phosphate coating and in service. .

It has been concluded that the corrosion in all cases re-sulted either directly or indirectly from borated water finding its way to the vessel flange (outside the sealing rings). All signs in-dicate that the aqueous solution had lain on the flange and countersunk areas around the stud holes. The solution vaporized upon vessel heatup and/orevaporatedupthroughtheheadflangetocorrodetheareaatthe top of the studs and the washer. There is no evidence to indicate that the solution attacked the studs by getting underneath the washer or nut.

All evidence indicates the corrosion to be due to attack by boric acid solution. The Parkerized coating offers no special corrosion protection in this case.

The source of the borated water was primary coolant which accumulated on the vessel flange during venting operations conducted after filling the pricary system. Venting equipment at the Palisades Plant is being modified such that there is no possibility of getting

Dr. P. A. Morris 1+

December 17, 1971 borated water on the reactor vessel flanges during venting operations in the future.

The effects of the reduction in the cross section of the studs (resulting from refurbishing) were considered during the de-velopmental stages of the rework procedures. This analysis indicated an acceptable change. The final Stress Report will be supplemented to include the changes due to refurbishing. The two studs that under-vent further metallurgical investigations will be documented separately in the final Stress Report.

The stud tensioning procedure has 'ceen reevaluated in li6ht of the slightly reduced stud cross sections. No revisions to this procedure are necessary since the differences in shaft extension during tensioning is negligible.

During discussions with Division of Compliance personnel, Consumers Power Ccmpany agreed to perfom additional inspections of the vessel studs and nuts during the first scheduled refueling outage.

This inspection will be performed in accordance with Item 1.8 of Table 1.3 1 of the Technical Specifications for the Palisades Plant. At 4

least ten (10) studs will be inspected. The surface examinations re-quired will be performed by the magnetic particle method. The first refueling outage is currently scheduled for September 1973 In addition, CE has agreed to establish a laboratory test program to further evaluate the compatibility of CE normal phosphate coatings and super moly-lubricant in the design environment of the studs. The details of this laboratory test program are currently being developed.

The cause of the corrosion to the reactor vessel studs has been eliminated. The thorough metallagraphic examinations conducted -

revealed that the studs are in good condition. All studs have been refurbished to eliminate similar future difficulties in removal.

Yours very truly, Robert L. Haueter (Signed)

RBS/dmb Robert L. Haueter Electric Production CC: Boyce H. Grier, Superintendent - Nuclear USAEC

o o ATTACREliT 1 REPORT OF II;VESTIGATION OF CLOSURE LEAD STUDS COI; SUERS PC' DER CO.vPANY PALISADES PLAITf C-E CO M ACT P.966A December U2, 1971

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O O December 12, 1971 CO:7 TRACT 2966A CONSUMERS POWER CO.

PALISADES PLMir CIOSURE HEAD STUDS INTRODUCTION It had become necescary to remove the vecsel head. Upon starting to remove the studs it was noted that a ructing condition was pre.sent, which was apparently caused by spillage of borated water and possibly a dichromate solution. Ee-cauce of the rusted condition, C-E concidered it desirable to closely examine the studs to determine whether or not there was any damage even though it was considered unlikely. C-E arranged for the removed studo to be sont to the stud manufacturer for clean up and careful examination by ".nagnaglo", and to have C-E personnel present.

In refurbishing the studs the manufacturer reground the threads, and machined the chank using a carbide tool removing 0.010 to 0.015 inches from the stud

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shank diameter. Upon "engnaglo" testing, 20 of the total of 54 studs exhibited several linear indications. All indications were in the chank portion of the studs and were in a circumferential orientation. Liquid penetrant testing was also per-formed at the canufacturer and no indications were found in this orientation.

No indications were present in the threaded portion of the studs. The indications varied in length up to a taxitum of 1-3/h inch. These studs are 7 inches diameter and 56 inches long. They are made to requirements of C-E Specifications as follows:

Material and Ultrasonic Testing C-E Purchase Spec. No. P0H16(c)

A540 Grade B24 Class 3 "Magnaglo" Testing (both before and after threading)

C-E IGP Spec. No. 2.4.2.5(a) and ASTM E138-63 Phosphate Coating C-E 162 Spec. No, h 4.4.l(a)

On Friday, December 10, 1971, two of the refurbiched studs were received for metallurgical investigation. One of the two was representative of the most pronounced "magnaglo" indications (ykk), and the other stud was representative of the average "magnaglo" indication appearance (#43). The stud ph4 exhibited 13 indications, mostly in the central section of the shank. These varied in circumferential length from 1/8 inch to 1-3/4 inch.

4 O O CONCLUSIONS

1. Indications were disclosed by "nagnaglo" testing. These were cir-cumferentially oriented.

2. Examination of the indication areas by metallography (both etched and un-etched), at the original surface and to depths at which the "tagnaglo" indication disappeared, revealed that no " defect" was present at any stage.

3. The "tagnaglo" indications are present in a right hand thread pitch orientation of soneuhat steeper helix angle than that of the present surface finish. The indications result fron slight differences in taterial magnetic permeability properties probably caused by slight variations in surface cold work induced in earlier tachining steps and possibly intensified by heating incurred in phosphate coating and in service.

4 "Magnaglo" indications of virtually identical appocrance were present in a stud of the same size frca another contract manufactured with the same procedure, and subjected to a hydrostatic test use but not service. The "tagnaglo" test was also perforned after removal of the phosphate coating.

5. The extensive examination confirms that, without any doubt, the subject studo are satisfactory for use.

Stud Manufacture C-E purchased the raterial for these studs es 7-1/2 inch diameter round bars on C-E Purchase Order No. h6 60lb4 The vendor is believed to have straightened the bar stock on a " bulldozer" (press) and not to have used a rotary straightener.

The bars were assigned C-E Code No. D-3816. C-E subcontracted the nachining on C-E Purchase Order No. 46 62329 Machining and "magnaglo" testing vere per-forted and the studs returned to Chattanooga where they were phosp' ate coated on C-E Purchase Order No. 47 47464 After phosphate coating no further "magnaglo" testing was performed.

The stud manufacturer ground the threads, and machined the shank using a carbide tool. The rough cut on the chank was to a depth of 0.040" to 0.050" per side using a 0.015" to 0.018" feed. The finish cut on the shank was with a carbide tool with 1/32" nose radius at 200 feet per minute with 0.009'to 0.010" feed to a depth of 0.010" to 0.015" per side. The cut was in a right hand thread direction with the stud chucked at the top end and a steady rest near the bottom end threads.

Stud Use The studs have "seen" a total of four prestressing cycles - one at C-E on hydro-static test, and three at the job site. The studs had reached a tetperature in service of approximately 500 F. On each of these cycles a lubricant was used.

This lubricant is " Super-Moly". It contains an " inhibitor". It is molybdenum dicuphide with mineral oil base.

O O Other Studs Two studs of identical design available in Chattancoga from another contract were exanined simultaneously with the subject studo. These studs were of identical manufactire except the phosphate coating was perforted by a different vendor.

Each of these studs had been used on a shop hydrostatic test. One was "tagnaglo" tested with the phosphate coating left on and one after removal of the phosphate conting.

METALLURGICAL IUVESTIGATIOy Ittediately upon "tagnaglo" exatinatica by experienced personnel at C-E, it was recognized that the indications disclosed were note form of non-relevant indication and did not constitute a " defect". Evnninat. ion procedure by "tagnaglo" vas performed with equipment and technique duplicating that used by the stud manufacturer and with identical results, as confirced by an employee of Chattanooga Nuclear Quality Control Departtent who was present at the testing at the stud manufacturer and at the testing of the returned pieces at C-E laboratory.

Procedures and examinations to confirn this conclusion are given below.

After the "tagnaglo" testing results obtained at the stud manufacturer were duplicated on equiptent at Metallurgical Research and Development Laboratory in Chattanooga, a series of tetallographic exeninations were tade directly on the

- stud surfaces at the location of "tagnaglo" indications. Exanination was performed after a minitum enount of total vaa renoved from the surface (0.001" to 0.003")

and after probe grinding to various depths up to 0.030" which partly or completely removed the "tagncE l o" indications. Probe grindins was controlled to expose completely the entire subsurface zone associated with "magnaglo" indications to direct metallogrcphic viewing. Quality of the metallographic finish and metallographic ctch vere fully ec= parable to conventional laboratory preparation of stall specimens. Viewing was with a binocular laboratory microscope of superior optical performance (Leitz ND) at tagnification of 50X to 1000X. The visual exanination through the microscope was fully comparable to laboratory bench metallegraphy in all respects and no compromise was necessary regarding thorou6h ness of exanination. For these reasons, it was not necessary to destructively section any of the studs to obtain unequivocal results and no further information is to be gained by destructive sectioning.

Stud Number h4, palisades Probe grinding 0.013" deep was perforced on stud #h4 by the stud manufacturer in an attempt to establish the depth of the condition causing the "tagnaglo" indications. As the rough surface appeared to obscure the "tcanaglo" results, this spot was carefully polished with COO grit to avoid more than 0.001 additional metal removal and to obtain a better surface for testing. Afterwards this spot was examined repeatedly at the sane test conditions used at the stud manufacturer and at higher and lover field strength.

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IETAIJAT30I0AL IL"ESTIGATYOIl (Cont'd.) ,

"F.agnaglo" indications were not precent doun in the 0.013" deep excavation ~Nt could be seen at the edge of the excavation. Thisexcavationwas31-5/8"below top end.

An area showing indications, 32" from the top end of stud //44, was polished metallographically to a depth of 0.003" below the original cachined surface.

"!bgnaglo" indication was still present in this area after 0.003" metal removal.

This area was examined up to 1000X as polished and arter etching with nital.

Iio indications of defects were found.

One circumferential indication about 32 inches from the top end of stud //4h was l examined metallographically by grinding two dimples, about 0.020" deep, at the two ends of the indication until the "cacneglo" indications were no longer present, leaving the center portion unground. The dimples and the unground portion were then polished tetallographically, after markira the unground portion of the in-dication with a center punch. /d'ter poliching, the unground portion and the slope - , _

of the dimple were exnmined at magnifications up to 1000X, simulating the examination of a cross section throu6h the ind'. cation. Iio defects or other abnormalities were detected, either in the as-polished or etched condition.

Stud liumber 43, Palisades Areas showing circumferential indications in stud #43 were examined in a similar tanner. Two adjacent indications, about an inch long were ground and polished so as to leave an unground portion. After polishing to a depth of 0.013" and 0.029", the indications disappeared at the bottom of the dimples. The unground portion was punch marked to identify the indication line, then polished lightly (about 0.001"). Fleroscopic examination revealed no defects. The slope of the dinples was alco examined microscopically after metallographic polishing into the area shoving no "tagnaglo" indications. This slope area, which was in effect a cross section through the zone between indications and absence of indications, . . .

showed no evidence of defects.

Other Studs Two studs for another contract, which were in the shop and had not been in service, were also examined in a similar tanner. One stud, #52, showed "magnaglo" indications on the as-phosphated surface. Examination of the surface before polishing showed circumferential marking. On polishing, the visual evidence of the indication disappeared, although sone of the phosphate conversion coating was still present in spots. These spots disappeared after

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o 9 polishing to a depth of 0.003", and no defects or abnormalitics were visible.

Upon re-examination by "magnaglo", however, the indication una still present.

Another stud from the same contract, #53, was also examined after removing the coating by polishing in a lathe with emery paper. This stud also showed scattered circumferential indications by "mu6naglo" techniques. No further metallographic examination was performed on this stud.

Summary Close examination revealed that all of the circumferential1y oriented "magnaclo" indications are at a slight pitch angle at a slighth steeper helix angle than that of the present surface finish. This is probably the orientation of the pitch helix used in a cut previous to the final machining cut. The stud manufacturer reported use of a right hand pitch during their machining operation.

The "masnoglo" indications are also at a right hand pitch angle. The sensitive "magnaglo" test in undoubtedly revealing indications resulting frcm magnetic premeability variations probably caused by slight variations in surface cold work induced by tachining and possibly intensified by heating incurred in phosphate coating and in service. Such cold work may have been introduced by another fabrication operation not present 4 identified.

Results of the exncination described above have conclusively verified the judgment that circumferential "mcanaglo" indications on these studs are "non-relcvant" and are not defect indications.

Technical evaluation was performed prior to the removal, during refurbishing, of the 0.010" to 0.015" stock from the chank of the studs. The analysis indicated an acceptable change. The final Stress Report will be supplemented to include this change.

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E m m M3Mnhm MGCum S' L. Kornblith Jr CO , . Pa0LLUG AT PALICADES AND 'ww.u;i ICINT 3 Attached cro copica of the propo cd TZ3 plans for 9

4 'g;=e3 ,, g g,g;3ge gg'enj,g gg CO investiCatinc:

I n. T. Car 1 con # CO 1. Eclic: des Denetor Vesoel Stud.Corronion Problem.

" 2. Tu.:ty Ibint 3 nelief valve needer Isilure.

2. Jce Collins of the Tcchnical Oupport Branch 1 -

has been c:cicaca to tche the lead in these inven-ticstir as. 'C2e Inspection and Enforec=cnt Branches vill be hept inferr.ca of the at: cults of the inves-tication as it progresces.- A pro =pt referral of anY.e g infor:::stica to TC3 vhich would not normally cone to 1 our attenticn yould be apprcetated.

9, 'Ihe aboro investigntions and assignments have been 5 L' approved by Mr. L. D. Lov, Director, Division of 4: Ccsplicce.

cc: 11. D. I' armer, CO 9' , U. J. .C@ma, C0 l Willia:s D. Famer ,

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