ML20205Q004

Rev 00 to NSP-27Q-301, CRDM Repair Adapter Plug Fillet Weld Evaluation

ML20205Q004
Person / Time
Site:	Prairie Island
Issue date:	02/12/1998
From:	STRUCTURAL INTEGRITY ASSOCIATES, INC.
To:
Shared Package
ML20205P991	List: ML20205P989 ML20205Q004
References
NSP-27Q-301, NSP-27Q-301-R, NSP-27Q-301-R00, NUDOCS 9904210060
Download: ML20205Q004 (9)

Text

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CALCULATION FILE No: NSP-27Q-301 STRUCTURAL mmRIn PACKAGE PRoJEcr No: NSP-27Q Associates, Inc.

PROJECT NAME: CRDM Repair Adapter Flug Fillet Weld Evaluation  !

I CLIENT: Northern States Power CALCULATION TITLE: Evaluation of Limiting Flaws for Structural Adequacy in CRDM Repair Adapter Plug Fillet Weld Evaluation at Prairie Island Unit 2 PROBLEM STATEMENT OR OBJECTIVE OF THE CALCULATION:

Demonstrate that the through-wall flaw size detectable by visual examination is less than the critical flaw size for both axially and circumferentially oriented flaws.

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Project Mgr. Preparer (s) & '

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1.0 INTRODUCTION

In support of the use of visual ==inadon rather than dye penetmnt examination of the completed fillet weld for the adapter plug at Prairie Island Unit 2, StructuralIntegrity Associates (SI) performed an evaluation to determine the critical flaw size in the repaired location. The purpose of this analysis is to demonstrate that a through-wall flaw could be detected by visual examination having a size which is sufficiently smaller than the critical flaw size, thus assuring sufficient safety margins. NSP will review the critical flaw sizes dete ia=1 in this calculation to con, fhm that the resulting sizes are detectable with margin by the visual technique.

4 2.0 GEOMETRY

'Ihe design geometry of the repair is illustrated in Figure 1. For the purpose of the present evaluation, the component was modeled as a pipe with outside radius equal to the distance from the ddve centerline to the outer most fillet weld radius (3.44 inches). The wall thickness of the cylinder was made equal to the minimum anticipated fillet weld thickness (0.44 inches with effective thickness of 0.265 inch), as shown on Figure 1. His geometry is considered a reasonable representation of the actual design geometry. Through-wall axial and circumferential I

flaws were evaluated. He model geometry is shown in Figure 2.

e 3.0 - APPLIED STRESSES I

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For conservatism, the applied stress was assumed to act as a membrane stress at the Code allo'wable membrane stress magnitude (P,, = S.). No distinction was made between the hoop and axial directions in this regard, although realistically, the axial direction should be closer to half of this value and is primarily composed of stress due to pressure. Bending stresses are small cormpared to the membrane stress since no loads, which would induce primary bending stresses, are present at this location.

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4.0 MATERIAL PROPERTIES .

The allowable stress, S , was taken to be 16.2 ksi at 650' F which is typical of 304 stainless steel.

The Alloy 625 to be used in the fillet weld has a significantly higher allowable stress at this tempemture so use of the stainless steel value is censervative. The flow stress for this component was taken as 3S per ASME Code Section XI Appendix C [1].

5.0 f ANALYTICAL APPROACH l

L The limit load (net section collapse) method is used to detennine the allowabic through-wall flaw leng1h at the fillet weld location. LEFM is not necessary at this location because the fluence is well below that required to significantly reduce the material fracture toughness. This method is described in ASME Code Section XI Appendix C [1].

Two cases were studied. These were:

1. Through-wall axial flaw: Limit load.

2. Through-wallcircumferentialflaw: Limit load.

1 No Code safety margins were included in this evaluation, since the objective is to get a reasonable view of the relationship between detectable and critical Daw sizes.

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6.0 RESULTS These cases follow the methodology presented in ASME Section XI,IWB-3641 and Appendix C

[1].

6.1 Through Wall AxialFlaw: Limit Load The I pregram pc-CRACK [2] was used to perform the analysis. The pe-CRACK results are ed in Appendix A to this report. The conclusion is that an axial flaw could be at least 4.17 inches long before leadmg to incipient collapse. This is much longer than is physically achievable, since cracking would be expected to be confined to the weld material and vicinity, which, in the axial direction, extends less than 1 inch.

6.2 Through Wall CircumferentialFlaw: Limit Load The analysis was based on the methods of Section XI Appendix C. The EPRI program DLL [3]

wasI also used to perform the analysis. The analysis assumed a through-wall circumferential flaw, and determined the critical flaw length using limit !aad techniques. The conclusion is that such a flaw could be 131* around the cylinder before reaching a critical size. This corresponds to a flaw approximately 6.95 inches long. Computer output is included in Appendix B of this report.

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7.0 CONCLUSION

S The above results demonstmte thar, under a variety of conservative assumptions, the critical flaw size predicted for the repair geometry is in all cases significantly longer than the flaw length which is expected to be detectable by a visual ex=imtion under magnification. as proposed by NSP. This will be confumed by NSP.

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'. 8 8,0 REFERENCES .

1. ASME Boiler and Pressure Vessel Code, See: ion XI, Appendix C,1989 Edition, No Addmda .

2. StructuralIntegrity Associates, pc-CRACK, for Windows, Version 3.0, March 1997.

3. BWR Vessel and Internals Project, "BWR Core Shroud Distributed Ligament Length (DLL) Computer Program (BWRVIP-20), Electric Power Research Institute, APRI AP-107283, December 1996 i, f m i

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r Adapter f R R = r + 1/4" + 3/8" s 3.44" I

ickness of Cylinder Used in Anaksis .

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"= 0.265* = (5/8)*0.707-v (1/4)*0.707 Center Line Where %, = gap Figure 1 Revision 0 Preparer /Date ,ggp Checker /Date g g/gg8 FileNo. NSP-27Q-301 Page 6 of 7 I

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Figure 2 Revision 0 Preparer /Date [ggf Checker /Date @ gig 45 File No. NSP-27Q-301 Page 7 of 7

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ATTACHMENT 2

SUMMARY

OF C AMERA TESTING l

l WELDING SERVICES INCORPORATED l

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U1PLCRDM relief req. DOC j

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- 1 ll 1 Welding Services Inc.

2=s avtmo count ucacaon accm an rE1EP5fCNE (409 4524D5 mos nu242 _

June 21,1995 Mr. Dick Cooper Nonhern States Power Company 1717 Wakoonde Drive East

"/cIch,MN 55089 FAX: 612-3304603

SUBJECT:

Pmirie Island Nuc! car Plant ,

WS1 ReferenceNo.: 35049-2 DearMr. Coopen Per your n: quest, we have perfonned seve=1 tests to evaluate de espabilities of 6e camera system used in the performance of 6e wcld repair of Prairie Island's CRDM Seals. W intent of ,

1 this testing is to provide data to be used by NSP to evaluate the adequacy of this camera for the petfcenance of adequate visual inspc:tien of the wcld overby. The testing described was not performed as a safety related procedure. The testing was perfonned as Collows:

1. The video front end of the WSI weld head was cccnected to aVCR a d monitor of tbc sac make and model as the system used on site. l

2. A mocle.:p of a canopy seal housing similar in configuration to the Pmirie Island design was ovedeyed in a similar conEgaration as tbc repdr performed ar the site. A .0005 inch diarteter wire and a .001 inch diameter wire each. 4 inches long, were taped to the surface of l the weld overlay on the housing.

3. 'Ibc two wires were filmed using the weld head front er.d, and the weld head lighting for il!umination.

4. WSI's site QC representative, Gay Caul, reviewed the tape and was able to see both wires on the surface of the weld.

A copy of the tape, samples of the two wires used, and additional camera Information are included with this letter for your review. P! case !ct me know ifyou need additional infocnation.

Sincerely,

% s.d4 Pedro E. Amador

SeniorProjec: Manager 3sm.zooc

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