ML20031F872
| ML20031F872 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 10/07/1981 |
| From: | Curtis N PENNSYLVANIA POWER & LIGHT CO. |
| To: | Haynes R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, PLA-938, NUDOCS 8110200500 | |
| Download: ML20031F872 (4) | |
Text
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PPal Pennsylvania Power & Light Company Two North Ninth Street
- Allentown, PA 18101 + 215 I 770L5151 Norman W. Curtis Vice President-Engineering & Construction-Nuclear 215 / 770-5381
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October 7, 1981 OOI Mr. R. C. Haynes U.
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Director, Region I U. S. Nuclear Regulatory Commission 1/
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SUSQUEHANNA STEAM ELECTRIC STATION FINAL REPORT OF A DEFICIENCY INVOLVING INADEQUATE THROAT THICKNESS ON SMALL PIPE SOCKET WELDS ERs 100450/100508 FILES 821-10/900-10 PLA-938
Reference:
PLA-894 (8/5/81)
Dear Mr. Haynes:
This letter serves to provide the Commission with a final report of a deficiency involving socket welds on small pipe. This deficiency was originally reported in PLA-894 and the information contained herein is submitted pursuant to the provisions of 10 CFR 50.55(e).
The attachment to this letter contains a description of the problem, its cause, safety implications and the corrective action taken and planned to preclude recurrence.
We trust the Commission will find this information to be satisfactory.
Very truly yours, N. W. Curtis Vice President-Engineering & Construction-Nuclear h
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l Attachment "8110200500 811007'.
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Mr. R. C. Ilaynes October 7, 1981 l
cc Mr. Victor Stello (15)
Director-Office of Inspection & Enforcement U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Mr. G. Mcdonald, Director (1)
Of fice of Managette7t InformTtic n & Program Control U. S. Nuclear Re olatory Comntission v
l Washington, D.C. 20555 Mr. Gary Rhoads U. S. Nuclear Regulatory Commission P.O. Box 52 shickshinny, PA 18655 l
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ATTACHMENT TO PIS-938 SUBJECT Several socket welds in "Q" systems were discovered to have inadequate throat thickness.
DESCRIPTION OF DEFICIENCY Bechtel NCR 6963 identified a problem.with small pipe socket welds made using the GTAW (Gas Tungsten Arc Welding) process. The welds did not have the theoretical throat thickness as required by ASME Section III, sub-article NB-4427 and figure NB-4427-1.
This deficiency was discovered while reworking the Instrument Gas line SP-CCC-201-1 to implement design revisions. Further investigation revealed that a total of 15 welds (12Q and 3 non-Q) on various plant systems did not have adequate throat thickness.
CAUSE OF THE DEFICIENCY Based on the results of investigations into the extent of she pr)blem (see CORRECTIVE ACTION below), one site welder was determined to be responsible for all of the nonconforming welds. The inadequate throat thickness was determined to be the result of a lack of complete penetration at the root of the pipe socket welds. These investigations also determined that the cause of this deficiency was the welding technique employed by the subject welder. The welder used the GTAW process when making the root pass for the deficient welds. The welder apparently lacked sufficient experiew;e with the GTAW process to realize that penetration to the root of the weld was not being achieved.
ANALYSIS OF SAFETY IMPLICATION The 12 deficient Q socket welds are in the following systems:
Emergency Service l
Water, HPCI Turbine and Auxiliaries, Residual Heat Removal and the Core Spray Systems. The insufficient throat thickness in these 12 welds could cause weld failure. Failure of one or more of these welds could possibly affect the ability to safely shut down the plant. Therefore, the subject condition has been determined to be a significant deficiency in construction reportable under the provisions of 10 CFR 50.55(e).
CORRECTIVE ACTION In order to ascertain the extent of the problem, information radiographs were taken of 208 sample socket welds. This sample represented the welds made by 26 welders including the subject welder. These 208 welds included both SMAW (Shielded Metal Arc Welding) and GTAW processes in carbon and stainless steel materials of various schedules. Review of these information rAciographs indicated that all GTAW socket welds made by the subject welder prior to re-training were of questionable adequacy. Review of the information rac'iographs for the SMAW socket welds made by the subject welder, however, did not Jelicate a problem with lack of penetration in the root pass. Additionally, review
.3 che information radiographs for the socket welds made by all other welders did not indicate problems with lack of penetration in either process. Therefore, the problem was determined to be isolated to the GTAW socket welds made by the one welder.
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j ATThCHMENT TO PLA-938 In the disposition to NCR 6963, direction was given to the field to replace all socket welds in lines CCC-201-1 and CCC-201-2.
Diaection was also provided to identify and measure (ultrasonically) the actual throat thickness of all ASME Section III, Class 1, 2 and 3 and ANSI B31.1 critical socket welds made by the subject welder.. Procedure TMSWl, which included the code criteria for theoretical throat thickness, was provided for this work. Socket welds which were measured and found to meet the acceptance criteria were considered acceptable.
A total of 775 ASME Section III and ANSI B31.1 critical socket welds (all made by the subject welder) were measured. Seven hundred and sixty (760) of these welds were determined to be in compliance with the code requirements for theoretical throat thickness and therefore considered to be acceptable. The balance of 15 welds (12 Q socket welds and 3 non 7 socket welds) did not have adequate throat thickness and hence required correction.
The fifteen welds found to have insufficient throat thickness will be replaced or built up to the required theoretical throat thickness. They will then be examined in accordance with the requirements of the fabrication and installation code as well as subjected to the throat thickness measurement to verify this dimension.
The rework / replacement of 13 welds has been completed and the remaining.two welds are forecasted to be completed by October 15, 1981. The rework / replacement of these welds is being documented by NCR 6963.
CORRECTIVE ACTION TO PRECLUDE RECURRENCE The subject welder has received additional instruction and training in the use of the GTAW. process for pipe socket welds. Destructive testing and information radiographs made after this period of retraining have verified this welder's ability to achieve penetration at the root of the socket weld.
Although the examination of 208 socket welds made by 26 welders using both the SMAW and GTAW processes confirmed that the problem identified represented an isolated case involving only one welder, all welders involved in making socket welds have been instructed in welding techniques which will result in full root penetration.
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