ML20086Q709
| ML20086Q709 | |
| Person / Time | |
|---|---|
| Site: | 05000471 |
| Issue date: | 07/28/1982 |
| From: | Lyons B HAYWARD TYLER PUMP CO. |
| To: | Fortuna R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| Shared Package | |
| ML20086Q645 | List: |
| References | |
| FOIA-83-439 NUDOCS 8402280087 | |
| Download: ML20086Q709 (4) | |
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P. O. Bo 92 80 Industrial Parkway Burlington, Vt. 05402 (802) 863-2351 July 25', 1982 Mr. Roger Fortuna Acting Chief of Investigations Office of Inspection & Enforcement U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Re:
Havvard Tyler Pumo Company (HTPC)
Dear Mr. Fortuna:
During their visit to HTPC's Burlington plant the week of July 12, Messrs. Dromerick and Peranich of your staff asked for HTPC's analysis j
The subject matters involved certain N-3 pumps of certain matters.
manuf actured for use at the Pilgrim 2 nuclear generating facility and the anti-rotation pin in the casing wear ring in pumps produced under Shop orders 8105/06.
The requested analyses are enclosed.
HTPC calls your attention to the fact that these analyses consist HTPC incurred of proprietary engineering and design information.
l significant expenses in obtaining and (in some cases) creating this infor-mation, and it could be of significant value to HTPC'c competitors.
Accordingly,1:~PC expects that NRC will not release this information to Should NRC receive a request to the public under any circumstances.
release the enclosed analyses, HTPC expects that the agency will notify the Company immediately, and at least ten working days before the agency makes any decision with respect to such request.
Sincerely, B.P. Lyons Chief Execut ve BPL/ gem 5$ - M 'D 8402280087 831221 PDR FOIA LODGE 83-439 PDR
^,,,m,,,,,-........
..Rayward Tyler
~ ' ~ n o-vp a-SHOP ORDER 8105/06 - ANTI-ROTATION PIN AND IMPELLER WEAR RING Based upon HTPC documents related to Shop Orders 8105/06, a question has arisen concerning whether an anti-rotation pin in the casing wear ring in those pumps might protrude so as to make contact with the rotating impeller wear ring.
This analysis demonstrates that such contact is unlikely to occur and, furthermore, should it' occur it is without consequence to the safety or operability of the eight pumps involved.
Wear rings are employed in HTPC's Code pumps to reduce or eliminate wear to the pumps' impellers and casings.
Impellers and casings are comparatively expensive parts.
The impeller wear ring is fixed to the impeller and rotates inside the casing with the impeller.
The casing wear ring is fixed to the casing and is designed not to rotate.
Allowing the wear to occur on the less expensive, easily replaceable wear rings is a cost-effective practice and one which is essentially universal within the pump manufacturing industry.
In order to be certain that the casing wear ring will not rotate, even should it come in contact with the spinning impeller wear ring, an anti-rotation pin is used to fix the casing wear ring in place inside the casing.
During the manufacture of the casing wear ring, a hole is drilled and tapped (i.e., threaded) in it for insertion of the anti-rotation pin.
A counterpart hole, not tapped, is provided in the casing itself so that the pin secures the wear ring to the casing.
The anti-rotation pin is threaded only to a suffi-cient length to be installed in the casing wear ring.
The drawings for the casing wear ring for the eight pumps in Shop Orders 8105/06 show that the hole for the anti-rotation pin would have been drilled (and most likely tapped, as well) all the way through the wear ring.
- Thus, certain circumstances are conceivable in which the pin might protrude beyond the casing wear ring toward the impeller wear ring.
(See drawing 01-401-326, Rev. A.).
In any machining process, there are specified tolerances.
Parts machined
-to be within their design tolerances will provide adequate clearance as neces-sary for the finished product to operate efficiently.
The following analysis applied this principle to an examination of the clearance between the' anti-rotation pin and the impeller wear ring.
In only one extreme set of circum-stances (a case with a low probability of occurrence) can the anti-rotation pin make contact with the impeller wear ring.
The effect of such possible contact on the functioning of the pump would be negligible.
This analysis considers three possible sets of_ circumstances.
The first situation considered is'that in which all the pertinent parts are machined to their most probable respective dimensions.
To calculate the most probable dimensions of all related parts, one assumes all dimensions are " nominal,"
i.e., in the middle of the tolerance range. -(If, for the sake of argument, one were to assert that a part might have been machined out of tolerance, the response is that it could only be machined smaller, so that the clearances involved would become larger and make contact even less likely.) laua
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.L calculatien / using nominal figures makas it apparant that ample clocranca e
is retained between the i=peller wear ring and the anti-rotation pin in these circumstances.
In second case, the dimensions of all the relevant machined parts are assumed to be at the far edge of their respective tolerances to provide f otation pin and the impeller wear ring.
=aximum clearance between the anti t
The circumstances in this second case serve only to increase the clearance over the nominal case.
Accordingly, this case presents no opportunity for metal-to-metal contact.
In the final case, the dimensions of all the relevant machined-parts are assumed to be at the exact opposite side of tolerance from what is assumed in the second case; i.e., in the third case dimensions are assuned which would minimize the clearance between the wear ring and the anti-rotation pin.
(As with the second case, the actual appearance of this case i
in any pump is highly unlikely since it assumes that all the related dimen-sions are skewed the maximum in one direction.
Assuming a normal distribu-In this tion, some dimensions would be abcve nominal and others below it).
third case, which is a " worst case" scenario in the sense of postulating the maximum possible metal-to-metal contact, there would be a maximum inter-ference between the anti-rotation pin and the impeller wear ring of 0.016 j
This third case assumes, among other things, that the pin inch in depth.
1 is threaded to its maximum tolerance thread length of 0.42 inches.
The pin can move no further through the tapped hole in the casing usar ring because the remainder of the pin is not threaded.
If the maximum possible depth of interference (0.016 inch) were experi-enced, the contact area on the impeller wear ring would be' ap' proximately 1/16 That is to say, the maximum cross-sectional area of metal-to-metal inch wide.
interference is about. 020 square inch.
Since the anti-rotation pin is made of 300 series stainless steel and the impeller wear ring is made of the sub-stantially harder 400 series stainless steel, if there were interference, the anti-rotation pin would quickly*/ wear away at the point of contact and the Heat interference would soon be eliminated with no degradation to the pump.
generation from the wearing away process would ba minimal due to the small-the casing is being contin-area of metal-to-metal contact and the fact that uously cooled by the fluids being pu= ped.
(The subject pumps are component cooling water pumps with a maximum design temperature of only 150 degrees F.
Whatever small amount of heat was generated would -be dissipated instantaneously.)
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The nominal cal-ulation uses the pin's mean threaded length of 0.39 inch.
Assuming the pin were driven as far into the hole as the threads would takeite, l
this would leave the pin protruding slightly beyond the casing wear ring.
l However, there would remain a clearance of 0.019 inch between the tip of the pin and the impeller wear ring at' nominal conditions.
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The subject pumps produce 350 HP at 1785 RPM.
Accordingly, once the pumps were turned.on at full power, the maximum conceivable' contact would be eliminated' entirely.
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In sum, the effect of the maximum possible metal-to-metal interference between the anti-rotation pin and the impeller wear ring would be essentially equivalent to that of failing to hand file a " metal burr" ff the pin.
The =uch more likely circumstance, o.f course, is tt' t there will be no interference between the pin and the impeller we..r ring.
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