ML20195D151
| ML20195D151 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 05/12/1986 |
| From: | Foster D GEORGIA POWER CO. |
| To: | Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| GN-908, NUDOCS 8606020134 | |
| Download: ML20195D151 (5) | |
Text
Georgia Fbwer Cornpany 8
Itst Office Box 282 Waynesboro, Georgia 30830 Telephone 404 554-9961, Ext. 3360 404 724 8'14. Ext. 3360 5'
L rW 1m; 7-\\
Georgia Power
- o. o. ro.t.,
Vice President
., 3 k '
Vogtle Project -
t!e southyn e;ectic system May 12, 1986 United States Nuclear Regulatory Commission File: X780102 Suite 2900 Log:
GN-908 101 Marietta Street, N.W.
Atlanta, GA 30323
Reference:
1.
Vogtle Electric Generating Plant - Unit 1, 50-424, NRC Report - Nos. 50-424/86-03 and 50-425/86-02 Module 8, Structural Steel 2.
GPC letter GN-864, April 17, 1986 Attention:
Mr. J. Nelson Grace Attached is the Georgia Power Company response to the additional clarification requested by the NRC Inspector during the site inspection visit from May 5 through May 9, 1986. The NRC request pertained to the unresolved items (URI) 86-03-03 and 86-02-03 identified in the NRC Inspection Report Nos. 50-424/86-03 and 50-425/86-02 regarding Module 8 Structural Steel, reference 1.
The NRC request for clarification pertained to long term effects on potentially overtorqued high strength bolted connections, identified in URI 86-03-03. The response-to URI 86-03-03 was provided earlier in Georgia Power letter GN-864, reference 2.
The enclosed response, attachment 2, is issued to clarify that there are no adverse long term effects on overtorqued bolts.
l Should you have any further questions, please contact us.
i This response contains no proprietary information and may be placed in the 3
NRC public document room along with our previous transmittal, GN-864.
I Very truly yo rs, i
/
. O. Fo ter e
MRT/00F/jwh cc: See Attachment 1 8606020134 860512 i
PDR ADOCK 0500 4
+Eol g
cc:
U. S. Nuclear Regulatory Commission Document Control Oesk Washington, D.C.
20555 Victor J. Stello, Jr., Director U. S. Nuclear Regulatory Commission Office of Inspection and Enforcement Washington, D.C.
20555 J. W. Thompson U. 5. Nuclear Regulatory Commission 7920 Norfolk Avenue Bethesda, MD 28014 Ms. Melanie A. Miller Division of Licensing Licensing Branch #4 Washington, D.C.
20555 Senior Resident Inspector U. S. Nuclear Regulatory Commission Vogtle Electric Generating Plant B. W. Churchill Shaw, Pittman, Potts & Trowbridge 1800 M Street, Northwest Washington, D.C.
20036 J. E. Joiner Troutman, Sanders, Lockerman & Ashmore Candler Building 127 Peachtree Street, N.W.
Atlanta, GA 30303 D. C. Teper Georgians Against Nuclear Energy 1253 Lenox Circle Atlanta, GA 30306
Page Two cc: William M. Hill NRC-IE (EWS-305)
Building East West / South Towers 4340 East-West Hwy.
Bethesda, MD.
20555 W. H. Rankin Suite 2900
' 101 Marietta Street, N.W.
Atlanta, GA 30323 R. E. Conway J. T. Beckham, Jr.
R. A. Thomas D. E. Dutton D. S. Read W. T. Nickerson D. T. King K. Wiedner P. D. Rice R. H. Pinson C. W. Whitney J. A. Bailey F. B. Marsh J. L. Vota C. W. Hayes S. H. Freid W. C. Ramsey R. T. Oedamer J. S. Hempstead W. M. Wright R. W. McManus G. C. Bell J. E. Seagraves M. H. Googe H. Walker J. Starnes (INPO)
O. Batum Document Control Project File RR Reading File (Letter Only) i 0155h/132-6 1
Page 1 of 2 High Strength Bolted Connections In response to the request by NRC during site inspection visit from May 5 through May 9, 1986, the following clarifications are provided relative to long term effects on potentially overtorqued high strength bolted connections.
General High-strength bolts (A-325 or A-490) installed by the turn-of-the-nut method acquire a preload higher than the proof load (proof load corresponds to the proportional limit). Such a preload is about 10% below the ultimate torque induced tensile strength of the bolt (refer to test results shown on Figures 4.7 and 4.8 of the book by Fisher and Struik, reference 1).
Thus, any inadvertently overtorqued bolts in the VEGP structural steel connections might have a maximum of 10% increase in their preload. This small increase in the preload should have minimal effect on the long-term behavior of the bolts.
Corrosion Bolts with high sustained tensile stresses are susceptible to stress and hydrogen embrittlement types of corrosion leading to delayed, brittle type fractures. Since the bolts are installed with high preloads above the proportional limit, material quality and heat treatment processes are controlled to achieve surface hardness to be within specified ilmits. As a direct consequence, high strength bolts of the types A-325 and A-490 have historically performed well without problems from corrosion failure in most environments (refer to Section 4.8 of reference 1). Therefore, an increase in the preload to near ultimate from overtorquing should have mininal contribution to corrosion failure. The increased relaxation less favorably decreases the preload, as explained below:
Relaxation Relaxation causes the bolts to lose some of their preload with time following installation.
Test results have shown the relaxation loss to be about 8% of the preload and most of the relaxation occurs within the first day (refer to Section 4.4 of reference 1). Any increase in preload from overtorquing entails an increase in the relaxation loss, because the relaxation loss is directly proportional to the initial tension.
Thus, a small increase in preload will cause a small increase in relaxation loss, thereby reducing the difference between an overtorqued bolt and a properly installed bolt.
3
r-s Page 2 of 2 Conclusion The design codes (AISC & ASME) have not expressed any concern about overtorqued bolts and there is no technical literature reporting corrosion or other allied problems with overtorqued bolts.
In addition, based on the reasons explained earlier, it is concluded that any inadvertent overtorquing of high strength bolts in VEGP structural steel connections has no adverse long term effects.
Reference:
1.
Fisher J. W. and Struik, J.H. A.,
Guide to Design Criteria for Bolted and Riveted Joints, John Wiley and Sons, 1974.
0154h/136-6 4