ML20246G974
| ML20246G974 | |
| Person / Time | |
|---|---|
| Issue date: | 07/12/1989 |
| From: | Rouse L NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Didyk J CANADA ATOMIC ENERGY CONTROL BOARD |
| References | |
| NUDOCS 8907140291 | |
| Download: ML20246G974 (12) | |
Text
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July 12,'1989 f Atomic Energy Control Board ATTN: ~ Mr. J. P. Didyk P.O. Box-1046' Ottawa, Canada K1P 559
Dear Mr. Didyk:
On July 5,1988, Mr. Abe Ghosh of your staff requested information from Scott' Pennington of my staff'on the actions being taken by Superior Valve Company and the U. S. Nuclear Regulatory Commission (NRC) to resolve a cracking problem with packing nuts in Superior 1-inch UF cylinder valves. Mr. Ghosh enclosed a 6
letter dated June 16, 1988,'from CAMECO (formerly Eldorado Resources Limited) informing Superior Yalve Company that a total of six in-service Superior cylinder valves had been discovered with cracked packing nuts. CAMECO also requested Superior to disclose the extent that the cracking problem had been identified by other users of the 1-inch valve and any efforts initiated by Superior to have the American National Standards Institute (ANSI) N14.1 specifications revised. Mr. Ghosh also enclosed a letter dated June 21, 1988, trom CAMECO informing the Atomic Energy Control Board (AECB) of the cracking problem and stated that they were attempting to determine the scope of the problem and if widespread, would seek corrective action through revision of ANSI N14.1. Subsequent to these communications, discussions on the packing nut issue have been held with you and members of your staff by my staff. As you are aware, this issue has been brought to the attention of the ANSI Subcommittee N14-1 but no actions have been taken.
We would like to apprise you of.a recent problem identified with Descote 1-inch cylinder valves. Allied-Signal has found three unused Descote valves with cracked packing nuts. One of the identified valves has been tested by the U. S. Department of Energy's (DOE) contractor, Martin Marietta Energy Systems
-(see enclosed report). A second valve has also been tested at Descote's manufacturing facility in Lyon, France.
Enclosed is a copy of Descote's preliminary report dated June 14, 1989,.to Allied-Signal describing their findings.
Although the NRC has not viewed the cracked packing nut to be a major safety issue, we have kept UF, cylinder users (NRC and State licensees) informed of the problem and stressVd the need to have operators check for cracked nuts I
oefore and after valve use and to review their torquing procedures. We will keep you apprised of further information that we may receive on this matter and of any actions taken by the NRC.
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8907140291 890712 PDR MISC 8907140291 PDC
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i Atomic Enehgy Control Board 2
July 12, 1989 If the AECB or CAMECO has received any additional information from Superior,
- Descote,lor ANSI.related to cracked packing nuts, we would appreciate your
. keeping us informed.
4 Sincerely, Original Signed By-Leland C. Rouse, Chief Fuel Cycle Safety Branch Division of Industrial and-
. Medical Nuclear.' Safety, NMSS
Enclosures:
As stated
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}lY EXAMINATION OF DESCOTE PACKING NUTS The Technical Services Division, Paducah Gaseous Diffusien Plant (PGDP),
has examined a cracked packing nut from a one-inch Desecte cylinder valve,
$crial Number 1675. The failure mode or the nut wat interararular cracking.
The meta 11cgraphic structure of the cra:ud qut (uterial heat R 91) was different from other product heats of Oncote nuts e.,d r.uts, from $uperior Valves. The hardness profile of the nut indicates that significar,t residual stresses could have been present after t,s process'.ng of the original bar stock.
A residual stress analysis was perf>rmed on enet o! the side faces of the cracked nut using the procedure and ecmntations der.:ribed in ASTM E 837.
The maximum and minimum principal stress!:s were -11.0 ksi n.nd -16.7 kst.
These are significantly higher residual ~ stresses thto are leasured in nuts that have been stress relieved at 700'F.
Since the uterior surface stresses are compressive, it is expected that the tatorial at the base of the root of the interior thread would contain high ruidual tensile stresses.
The physical appearance of the surface suggests that the faces of the nut were ground.
It is suspected that surface f111shing cperations had induced the high residual compressive stresses.
Failures of nuts with similar serial numbers and the findings of the investigation sugges.ts tha's nuts produced from naterial designated R 91 and/or sur'tce gretcnd are susceptible to stress corrosion cracking.
TOTAL P.02
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Mark S. Fucich Vee Pres @entGeneralManager,
12010 Lakeland Park Blvd.
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Allied Signal Mr. Jerry Bishop, P1 ant Manager P.
O.
Box 430 Metropolis, IL 62960 RE:
Preliminar y Repor t on Descote Packing Nut Failure on 1" UFG, Serial Nos. 1675, 1689, 1694, Heat R91
Dear Mr. Bishop:
Attached please find the above referenced Report produced by the mother company Descote S.A.,
Feyzin, France.
We are working very hard to find out every detail.
Descote is committed to working with Allied Signal and other users of this product to produce the highest quality product under the most stringent quality control.
We are also committed to working with the ANSI Standards Committee as a partner to work towards improving current design.
Should you or your staff have any questions, please do not hesitate to contact our of fice at 1-800-666-3140.
The following is a list of all valves delivered in North America from Heat P91:
Heat No. of Valves Serial No.
Westinghouse R91 60 1539-1578 Allied Signal R91 200 1629-le2e i
El Dorado Canada R91 1
2079
- 1 n. zu.. rw rp P91 50 N T A - o.1 7 5 Shipments made 1986 - 1987 25646 Y
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We have this informat' ion and will users appearing on this list..
submit'our. report-to other Respectfully. submitted,
['
Mark S.
Fucich' Vice President / General Manager Descote USA, Inc.
MSF:Ide:
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-Jack' Honey, Allied Signal
. Matt Kosmidar, Allied Signal Mr. Rouse, NRC Scott Pennington,'.NRC Randy. Reynol ds, Martin Marietta Steve Blue, Martin Marietta Enclosure i
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SUBJECT:
REPORT ON PACKING NUTS FAILURE - ALLIED CHEMICAL 1" UF6 VALVES - SERIAL NO. 1675-1689-1694 1.
HISTORY November 86:
Order placed by ALLIED CHEMICAL for 200
- valves, 1" UF6 (P.O 054/95250).
Nov.20th BG:
Shipment from FRANCE, Valves S.N.
1639-1838.
Packing nut Heat Number R91.
January 87:
Valves received by ALLIED CHEMICAL.
July 28 87:
MR. KOSMIDAR. informed us about the failure on the Valve packing nut, S.N.
1690.
Sept.2nd 87:
Phone conversation between MR. KOSMIDAR and HERVE CHATANAY; the conditions are clearly mentioned:
April 87 :
Installation of the valve on a-container after filling and cooling.
July 87 When the container is ready for shipment, the packing nut is failed on'all the circumference.
The NRC is informed.
The valve has not been heated and the packing nut torque has been checked:
140 ft. Ibs.
The container has been stored j
outside from April to July, J
1987.
I i
Sept.14 87:
DESCOTE answer to ALLIED CHEMICAL (attached).
Af ter return of the Valve, S.N.
- 1690, j
a metallurgical examination has been made:
4 The material is in conformity with the speci fication but it shows a large but acceptable INTERGRANULAR PRECIPATION (photographs to b= mailed separately).
Since that time, DESCOTE and its main french customer have conducted an in I
depth study.
I 1
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March 89:
Report X-423 has been mailed to MR.
J.
HONEY of ALLIED CHEMICAL.
l Apr. 18th 89:
DUSA is informed by ALLIED that packing nuts of Valves, S.N.
1675-1689 and 1694 are cracked..
The valves have never been used.
2.
ANALYSIS OF VALVES, S.N.
1675-1609-1694 2.1) 1 of the 3 valves has been examined by MARTIN-MARIETTA. (see their report and DESCOTE's anuwer).
2.2)
The Valve, S.N.
1689 has bEen returned to DESCOTE.
2.2.1)
After visual examination, no other apparent failure except the packing nut.
i 2.2.2)
PARTS EXAMINATION Stem (2) - Body (1)
-OK.
A dye penetrant control of the packing box does not show any cracks or swelling.
Packing Ring (7)
-there is a burr on the inside.
Either it was at the drilling or it has been caused by an over tightening of the stem in back seat (full opening).
Packing Gland (5)
-there is a bending of 0.10 mm at the upper part.
Possible Causes:
1) too high torque 2) thrust due to PTFE dilatation (expansion).
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1 0.2.3)
PACKING EXAMINATION
-Packing rings are flattened out and the volume between packing ring, packing gland, stem and body is completely filled.
It also shows the PTFE cold flow along the stem and packing gland.
It is comparable to photo # 20 of Report X 423.
2.2.4)
PACKING NUT EXAMINATION
-There is a large fracture on 5 faces of the hexagon.
l
-Except for the fracture itsel f, the dye penetrant control does'not'show any other sur f ace defects.
-The sur f ace finish of the hexagon faces is not normal.
The metal has been grinded or linen f aced on tne faces and angles.
It has not been shipped as it is.
-The machining marks on the hexagon have disappeared.
It is proof that some-thing happened af ter the shipment because:
DESCOTE buys round bars.
DESCOTE machines the hexagon from the round bars to guarantee:
-per fect stress distribution on the round bar.
-perfect dimensional control and sur f ace finish on the hexagon.
We have particularly checked this point since it is mentioned in MARTIN MARIETTA report, conclusion of which are questionable.
Test with Mercurous nitrate on bars and finished parts have shown no residual stress.
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A metallurgical' analysis has been L
ordered.. We are waiting for the l'
results but do not expect new L
information since investigations were.
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already made earlier on it concerning I
a packing nut cracked by a french user.
The metallurgy is totally in conformity
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with the speci fications.
3.
INTERPRETATION AND CONCLUSION 3.1)
Awaiting the. metallurgical report, the-fundamental element is the complete and total compression of the PTFE packing.
The report X 423 confirmed that with a torque of 150.ft/lbs, the packing fills up the volume between the stem, body, packing ring and packing
. gland only after retightening cycling operations at temperature.
The Valve, S.N.
1689 has certainly oeen subject to several retightening of the packing nut, even if the valve has never been installed.
~
It has been possible that:
1.)
Either by-DESCOTE before shipment; at that time we were analyzing the effect of tightening and these valves could have been retightened 3 - 10 times.
2.)
Either by the customer as a preventive action.
3.)
Or by both, 1 a r.L z Facts are evident:
The chamber is full and the PTFE cold flow is the result of a too important stress.
This is the phenomenon described in'the Report X 423.
3.2)
We are interested to know some additional points:
-Is there a systematic retighteneing
.nrocedure of the Packing nut aool i c abl e bv ALLIED?
If YES, at which torque?
How I
often?
-Did ALLIED modi fy its procedures or operations further to the incident on the
- Valve, S.N.
1690.
-Although the grinding on the sur f ace of the hexagon is not directly at the origin of the failure, we would like to know what could have generated this operation.
l
-Are the valves with packing ring heat R91 installed?
If YES, How many packing nuts cracked?
3.3)
TEMPORARY CONCLUSION An excessive tightening f the packing nut has caused the f ul fi l l ment ano the implementing of high ef forts due to thermic dilatation of the PTFE.
We think that the metallurgical analysis will shou a certain density of intergranuler precipitation in the material.
The combination:
Strength + Intergranular precipitation is the cause of the rupture.
1 l
L______..__._________
EP.Ps-DESCOTE FRANCE 33 78677885 1989-06-14 les24 G3-48 3
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i Mr Matt K0SMIDER ALLIED CHEMICAL HC/1ML
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NETROPOLIS, IL. 61960 UF6 valve nr'1690 USA t
packing nut erack September 14, 1987 b'
9 tar Mt KOSW195R, I
tt has been a pleasurt'to tak to you on the phont and to *Unu11 about the fattura of the necking nut of the 1 insk W6 etundet vatvu. annufactured by 9tSCOTE under serlat numbu ' 4600 dated CeXe6tA 1986.
r i
sa4ed on the information gathusd during out coaut44auan L.e.
.' 4
- the valve has ntytt seen hot Ed 1
.. the was fe *c!!ad in AptR 1987, when the. eyuiider
,. naa ed ier sMpuent aitu 40Udlfleation af W6 at-
" 'ambt h4
- tM 'patkl Inst sans ieund essektd (AUpped all aroundI in N'
'1 Jaff.1987 <
1-
'ths toteuk sees thecked during Autably on the packing nut
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at140ft.O We al4h to inform you about the folloising :
's) DESCOTE haa sold about ts 000 pleets l' inek W6 syundu '
valves that att stMetty manufactured according to the ANs1
- i 14.1-198t (new 1986) necording tAtusEt0ASpielfleatlens:
JSP-53t and E3 11t46, 4
b) Tht quau ty tentrata and tests carried out by CE.1 COTE on sach valve meet more tAan tat ANSI requirements
.thl4 44 Aoun on ti.L aUached comparative chart b.etaten ANS1/9 esc 0TE.
el PESCOTE acu ng a4 a manufacturer and not a4 a dialgner can enty taprove the pusuty of the fabricauen by laptenentim a
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j d) Komvu we have. numbered 12 easts of packing nut fallae among the 25 000 UF6 valves m1nufactured.
Tn all these cases \\lnetuding yours) the al. lot) 636 dt.tivered is perfeettuj confo.tm to the hS ERDAyfications and the
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dimensions d tJte parts ue in conformlbj with the. drawings.
Attacht.d are alt the matendal etrtlficates pertaining to the, valves of your 70 054/9525 Lt proves the accordance of oM suopb] with the spec 1 flea.tlons.
t) Pauulng our investigauons we have noted that a duple edeu.
Lation ' shows that the torque valut required by the. ANS1 (150 ft.lb) on the packing nut generates a tertdte stre.ngth which is vtry star af St yletdlng point.
At this flalt the Alloy 636 might be. subftet to either quick and bad aging provoking the grain dislocation on a stress covtoslon cAachin whleh lead sensequently to the dt.struction of the
(....)
metal. g f) Sued on the analysts ands
'n faltare we can be satt that the 12 cases of packing nut o
- there is no refestnee to the heat number anet thtAt are dlfferentheatnumbersinvolved
- thtAt is no referenet to the age of the valvt : 1 valves manufactured and put in service in 1985 have had a packing nut falta t Ln h nt 1987
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- there is no referenet to the sonditions of ast.
- s
- f. hest incidents happened to several customers who are not using de 4 ant ptocedures.
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'ih & W GC tklnk dat we can guarantet ut utAy exceptional natutt.ofthisnotsystemattephenomtnan.
O in conclusion we think that the risk of fsilme of the packing nut een onbj be de material change. finitively eliminated by a new design or by a DESCOTE ls dedded to axhe the ntetssary changes and has strendy worked on posslbt.t technicd.
Proposals a such ones nist first be dlmtssed and appove.d in thtdr pinc1ptt.ts) with u s end ustAs be the modlflention Ls subaltte.d to the US ERDAfortwfort ysis and appovat.
Should you agree with on appoath and wish to let us know about
~
you experience and technicalldtas pttase infora os according!g so that we can ensure coordination at our end.
Renalning at year dlsposal, YoMs SinccAtty,