ML20085B805

Rept of Investigatin of Closure Head Studs

ML20085B805
Person / Time
Site:	Palisades
Issue date:	12/12/1971
From:	CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:
Shared Package
ML20085B789	List: ML20085B800 ML20085B805
References
NUDOCS 8307080422
Download: ML20085B805 (6)

Text

,

i .

O O Decniber 12, 1971 CONTRACT 2966A CONSUMERS POWER CO.

PALISADES PLANf CIOSURE HEAD STUDS INTRODUCTION It had become necessary to remove the vessel head. Upon starting to remove the studs it was noted that a rusting condition was pre,sent, which was apparently caused by spillage of borated water and possibly a dichromate solution. Be-cause of the rusted condition, C-E considered 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 studs to be sent to the stud manufacturer for clean up and careful examination by "magnaglo", and to have C-E personnel present.

In refurbishing the studs the manufacturer reground the threads, and machined the shank using a carbide tool removing 0.010 to 0.015 inches from the stud shank diameter. Upon "magnaglo" testing, 20 of the total of 54 studs exhibited several linear indications. All indications were in the shank portion of the studs and were in a circumferential orientation. Liquid penetrant testing was also per-formed at the manufacturer and no indications were found in this orientation.

No indications were present in the threaded portion of the studs. The indications variedinlengthuptoamaximumof1-3/4 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 M&P Spec. No. 2.4.2.5(a) and AS M E138-63 Phosphate Coating C-E M&P Spec. No. 4.4.4.l(a)

On Friday, December 10, 1971, two of the refurbished studs were received for metallurgical investigation. One of the two was representative of the most pronounced "magnaglo" indications (#44), and the other stud was representative of the average "magnaglo" indication appearance (#43). The stud #44 exhibited 13 indications, mostly in the central section of the shank. These varied in circumferentiallengthfrom1/8inchto1-3/4 inch.

8307080422 711126 PDR ADOCK 05000255 G PDR r a

e.

i -

O O CONCLUSIONS

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

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

1 4 3. The "magnaglo" indications are present in a right hand thread pitch orientation of somewhat steeper helix angle than that of the present surface finish. The indications result from slight differences in material magnetic permeability

properties probably caused by slight variations in surface cold work induced

in earlier machining steps and possibly intensified by heating incurred in phosphate coating and in service.

.i

) 4 "Magnaglo" indications of virtually identical appearance were present in a stud of the same size from another contract manufactured with the same procedure, and subjected to a hydrostatic test use but not service. The j "magnaglo" test was also performed after removal of the phosphate coating.

i'

5. The extensive examination confirms that, without any doubt, the subject j

stude are satisfactory for use, 1

i Stud Manufacture t

' C-E purchased the material for these studs as 7-1/2 inch diameter round bars on C-E Purchase Order No. 46-60144. 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 machining on C-E Purchase Order No. 46 62329 Machining and "magnaglo" testing were per-i formed and the studs returned to Chattanooga where they were phosphate coated 4

on C-E Purchase Order No. 47 47464 After phosphate coating no further "magnaglo" testing was performed.

1 The stud manufacturer ground the threads, and machined the shank using a carbide tool. The rough cut on the shank 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 tcol with 1/32" nose radius at 200 feet per minute with 0.009,'to 0.010" feed to j 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 temperature 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 disuphide with mineral oil base.

A

l E (3 O t*

. G Q)

Other Studs

( .

Two studs of identical design available in Chattanooga from another contract were

! examined simultaneously with the subject studs. These studs were of identical l manufactire except the phosphate coating was performed by a different vendor.

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

METALLURGICAL INVESTIGATION Immediately upon "magnaglo" examination by experienced personnel at C-E, it was recognized that the indications disclosed were some form of non-relevant indication and did not constitute a " defect". Examinat. ion procedure by "magnaglo" was performed with equipment and technique duplicating that used by the stud manufacturer and with identical results, as confirmed by an employee of Chattanooga Nuclear Quality Control Department 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 confirm this conclusion are given below.

~

After +he "magnaglo" testing results obtained at the stud manufacturer were duplicated on equipment at Metallurgical Research and Development Laboratory in Chattanooga, a series of metallographic examinations were made directly on the stud surfaces at the location of "magnaglo" indications. Examination was performed after a minimum amount of metal was removed from the surface (0.001" to 0.003")

and after probe grinding to various depths up to 0.050" which partly or completely removed the "magnaglo" indications. Probe grinding was controlled to expose completely the entire subsurface zone associated with "magnaglo" indications to direct metallographic viewing. Quality of the metallographic finish and metallographic etch were fully comparable to conventional laboratory preparation of small specimens. Viewing was with a binocular laboratory microscope of superior optical performance (Leitz ND) at nagnification of 50X to 1000X. The visual examination through the microscope was fully comparable to laboratory bench metallography in all respects and no compromise was necessary regarding thoroughness of examination. 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 4 , Palisades Probe grinding 0.013" deep was performed on stud #W by the stud manufacturer in an attempt to establish the depth of the condition causing the "magnaglo" indications. As the rough surface appeared to obscure the "magnaglo" results, this spot was carefully polished with 600 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 same test conditions used at the stud manufacturer and at higher and lower field strength.

t .

J

i Ui O

!ETAILURGICAL IINESTIGATION (Cont'd.)

O "Magnaglo" indications were not present down in the 0.013" deep excavation but could be seen at the edge of the excavation. This excavation was 31-5/8" below top end. l An area showing indications, 32" from the top end of stud #44, was polished metallographically to a depth of 0.003" below the original machined surface.

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

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

No indications of defects were found.

One circumferential indication about 32 inches from the top end of stud #44 was examined metallographically by grinding two dimples, about 0.020" deep, at the two ends of the indication until the "magnaglo" indications were no longer present, leaving the center portion unground. The dimples and the unground portion were then polished metallographically, after marking the unground portion of the in-dication with a center punch. After polishing, the unground portion and the slope

of the dimple were examined at magnifications up to 1000X, simulating the j examination of a cross section through the indication. No defects or other abnormalities were detected, either in the as-polished or etched condition.

j Stud Number 43, Palisades 4

Areas showing circumferential indications in stud #43 were examined in a similar manner. 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 j

portion was punch marked to identify the indication line, then polished lightl,y (about 0.001"). Microscopic examination revealed no defects. The slope of the dimples was also examined microscopically after metallographic polishing into

'j the area showing no "magnaglo" 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, i

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

i l 4-J

f 1

?i ' ;.

. 1 poliching to a depth of 0.003", and no defacts or abnormalitiss vsre visible.

Upon re-examination by "magnaglo", however, the indication was 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 circumferentisl indications by "magnaglo" techniques. No further metallographic examination was performed on this stud.

Simwnary Close examination revealed that all of the circumferentially oriented "magnaglo" indications are at a slight pitch angle at a slightly 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 "magnaglo" indications are also at a right hand pitch angle. The sensitive "n:agnaglo" test is undoubtedly revealing indications resulting from magnetic premeability 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. Such cold work may have been introduced by another fabrication operation not presently identified.

Results of the examination described above have conclusively verified the judgment that circumferential "magnaglo" indications on these studs are "non-relevant" 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 shank cf the studs. The analyais indicated an acceptable change. The final Stress Report will be supplemented to include this change.

l I

i l

1 J