Information Notice 1985-65, Crack Growth in Steam Generator Girth Welds: Difference between revisions
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==Description of Circumstances== | ==Description of Circumstances== | ||
:In 1982 Indian Point Station Unit 3 had a leak at weld No. 6 on one of theirsteam generators (see Information Notice 82-37). Weld No. 6 is a full-penetration circumferential weld located in the transition zone betweenthe tube bundle and steam dryer areas, below the feedwater nozzles, andsubject to thermal cycling. The crack was started by corrosion and operatingtemperature fluctuations caused it to grow through the wall because of low-cyclefatigue. The repair method reduced the defects to an acceptable level.Ultrasonic examinations have been performed during outages since 1982 and inthe summer of 1985. Previously known indications that appear to have grown insize are being evaluated.In 1983 Surry Power Station Unit 2 performed ultrasonic examinations of theNo. 6 welds. The original construction weld at Unit 2 is 6 inches above theweld that attached the lower portion of all three replacement steam generatorsin 1980 (see attached sketch). The examination showed widespread indicationsof discontinuities on the inside surface of this weld in the "A" steam genera-tor. None of the indications seemed large enough to be rejected and it was8507290456 IN 85-65July 31, 1985 decided that they were surface blemishes of reflections from weld geometry. InMarch 1985, an ultrasonic reexamination was performed on the original construc-tion weld at Surry and larger, but acceptable, discontinuities were found inthe same locations. The inside surface of the weld in generator A wasvisually examined, but no defects were seen. However, when magnetic particletesting was performed at the request of the NRC, closely spaced linear crackswere found over a large portion of the circumference. The appearance of thesecracks was similar to those at Indian Point. The safety significance is thatsubstantial loss of secondary coolant could occur without warning if crackingdegradation continued undetected.The cracks in generator A were in a narrow band at the upper edge of the weldand covered almost the entire inside diameter. The cracks were as deep as 1/2inch and were covered by the surface oxide, which obscured detection by visualexamination. Generators B and C had numerous, smaller, circumferential cracksin the same location. To complicate matters, there were 10 unacceptablesubsurface indications in generator B, based on the requirements of ASMESection XI, IWB-3511. After a fracture and fatigue evaluation, these subsur-face indications were accepted by ASME IWB-3600. The surface cracks in allthree generators were removed by grinding; repair welding was not necessary.Weld No. 6 was made on-site and had high residual stresses as a result of thelow preheat and postweld heat treatment temperatures. The steel in the vicini-ty of the weld pitted when the secondary water contained high oxygen concen-trations (higher than 25 ppb) and contaminants such as chlorides and copperions. In addition to internal pressure, this portion of the steam generatorhas a change in cross-section and undergoes thermal cycling. Heat treatment ofthe nearby replacement weld in 1980 reduced the residual stresses, but couldnot undo any existing damage to the original construction weld. The cracks ranfrom pit to pit and grew to an unacceptable size in less than one inspectionperiod.At the next outage, the No. 6 welds in all three steam generators at Surry Unit2 will be partially examined by magnetic particle testing. The subsurfaceindications in generator B also will be examined by ultrasonic methods. Slowgrowing corrosion cracks are irregular in length and depth. When the cracksare located in the fusion line between the weld and the base metal, evaluationis very difficult by ultrasonic methods alone. Magnetic particle testing ismore sensitive than visual examination and supplements ultrasonic examinationswhere there is a possibility of surface defects. ASME Section XI specifies themaximum allowable planar indications and the methods of examination, but thesemethods may not be sufficient to identify indications and defects in all cases.Additional surface preparation, calibration notches, personnel training, andsmaller ultrasonic probes may result in a better understanding of the ultrason-ic | :In 1982 Indian Point Station Unit 3 had a leak at weld No. 6 on one of theirsteam generators (see Information Notice 82-37). Weld No. 6 is a full-penetration circumferential weld located in the transition zone betweenthe tube bundle and steam dryer areas, below the feedwater nozzles, andsubject to thermal cycling. The crack was started by corrosion and operatingtemperature fluctuations caused it to grow through the wall because of low-cyclefatigue. The repair method reduced the defects to an acceptable level.Ultrasonic examinations have been performed during outages since 1982 and inthe summer of 1985. Previously known indications that appear to have grown insize are being evaluated.In 1983 Surry Power Station Unit 2 performed ultrasonic examinations of theNo. 6 welds. The original construction weld at Unit 2 is 6 inches above theweld that attached the lower portion of all three replacement steam generatorsin 1980 (see attached sketch). The examination showed widespread indicationsof discontinuities on the inside surface of this weld in the "A" steam genera-tor. None of the indications seemed large enough to be rejected and it was8507290456 IN 85-65July 31, 1985 decided that they were surface blemishes of reflections from weld geometry. InMarch 1985, an ultrasonic reexamination was performed on the original construc-tion weld at Surry and larger, but acceptable, discontinuities were found inthe same locations. The inside surface of the weld in generator A wasvisually examined, but no defects were seen. However, when magnetic particletesting was performed at the request of the NRC, closely spaced linear crackswere found over a large portion of the circumference. The appearance of thesecracks was similar to those at Indian Point. The safety significance is thatsubstantial loss of secondary coolant could occur without warning if crackingdegradation continued undetected.The cracks in generator A were in a narrow band at the upper edge of the weldand covered almost the entire inside diameter. The cracks were as deep as 1/2inch and were covered by the surface oxide, which obscured detection by visualexamination. Generators B and C had numerous, smaller, circumferential cracksin the same location. To complicate matters, there were 10 unacceptablesubsurface indications in generator B, based on the requirements of ASMESection XI, IWB-3511. After a fracture and fatigue evaluation, these subsur-face indications were accepted by ASME IWB-3600. The surface cracks in allthree generators were removed by grinding; repair welding was not necessary.Weld No. 6 was made on-site and had high residual stresses as a result of thelow preheat and postweld heat treatment temperatures. The steel in the vicini-ty of the weld pitted when the secondary water contained high oxygen concen-trations (higher than 25 ppb) and contaminants such as chlorides and copperions. In addition to internal pressure, this portion of the steam generatorhas a change in cross-section and undergoes thermal cycling. Heat treatment ofthe nearby replacement weld in 1980 reduced the residual stresses, but couldnot undo any existing damage to the original construction weld. The cracks ranfrom pit to pit and grew to an unacceptable size in less than one inspectionperiod.At the next outage, the No. 6 welds in all three steam generators at Surry Unit2 will be partially examined by magnetic particle testing. The subsurfaceindications in generator B also will be examined by ultrasonic methods. Slowgrowing corrosion cracks are irregular in length and depth. When the cracksare located in the fusion line between the weld and the base metal, evaluationis very difficult by ultrasonic methods alone. Magnetic particle testing ismore sensitive than visual examination and supplements ultrasonic examinationswhere there is a possibility of surface defects. ASME Section XI specifies themaximum allowable planar indications and the methods of examination, but thesemethods may not be sufficient to identify indications and defects in all cases.Additional surface preparation, calibration notches, personnel training, andsmaller ultrasonic probes may result in a better understanding of the ultrason-ic indications. | ||
IN 85-65July 31, 1985 No specific action or written response is required by this information notice.If you have any questions about this matter, please contact the RegionalAdministrator of the appropriate regional office or this office.ar L. Jordan DirectorDivision of Eme gency Preparednessand Engineering ResponseOffice of Inspection and Enforcement | |||
===Technical Contact:=== | ===Technical Contact:=== | ||
P. Cortland, IE(301) 492- | P. Cortland, IE(301) 492-4175Attachments:1. Sketch of Steam Generator2. List of Recently Issued IE Information Notices | ||
Attachment 1IN 85-65July 31, 1985 Sketch Showing Steam Generator AORIGINALCONSTRUCTION6 N._- WELDN006/ 9980WELDTHAT ATTACHEDTHE REPLACEMENTSTEAM GENERATORS | |||
Attachment 2IN 85-65July 31, 1985LIST OF RECENTLY ISSUEDIE INFORMATION NOTICESInformation Date ofNotice No. Subject Issue Issued to85-6485-63BBC Brown Boveri Low-VoltageK-Line Circuit Breakers, WithDeficient Overcurrent TripDevices Models OD-4 and 5Potential for Common-ModeFailure of Standby Gas Treat-ment System on Loss of Off-Site PowerBackup Telephone Numbers tothe NRC Operations Center7/26/857/25/857/23/8585-6285-6185-60Misadministrations to Patients 7/22/85Undergoing Thyroid ScansDefective Negative Pressure 7/17/85Air-Purifying, Fuel FacepieceRespiratorsValve Stem Corrosion Failures 7/17/85Failure Of A General Electric 7/17/85Type AK-2-25 Reactor TripBreakerAll power reactorfacilities holdingan OL or CPAll power reactorfacilities holdingan OL or CPAll power reactorfacilities holdingan OL and certainfuel facilitiesAll power reactorfacilities holdingan OL and certainfuel facilitiesAll power reactorfacilities holdingan OL or CPAll power reactorfacilities holdingan OL or CPAll power reactorfacilities designedby B&W and CE holdingan OL or CPAll power reactorfacilities holdingan OL or CP; fuelfacilities; andmaterial licenseesAll power reactorfacilities holdingan OL or CP85-5985-5885-57Lost Iridium-192 SourceResulting In The Death OfEight Persons In MoroccoInadequate EnvironmentControl For Components AndSystems In Extended StorageOr Layup7/16/857/15/8585-56OL = Operating LicenseCP = Construction Permit | |||
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{{Information notice-Nav}} | {{Information notice-Nav}} | ||
Revision as of 19:01, 6 April 2018
SSINS No.: 6835IN 85-65UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF INSPECTION AND ENFORCEMENTWASHINGTON, D.C. 20555July 31, 1985IE INFORMATION NOTICE NO. 85-65: CRACK GROWTH IN STEAM GENERATORGIRTH WELDS
Addressees
- All nuclear power pressurized water reactor (PWR) facilities holding an operat-ing license (OL) or a construction permit (CP).
Purpose
- This information notice is provided to alert recipients of a potentiallysignificant problem pertaining to the growth in indications in steam generatorcircumferential welds. Ultrasonic examination had determined previously thatthe welds were acceptable. It is suggested that recipients review the informa-tion for applicability to their facilities and consider actions, if appropri-ate, to preclude a similar problem occurring at their facilities. However,suggestions contained in this information notice do not constitute NRC require-ments; therefore, no specific action or written response is required.The NRC is continuing to evaluate pertinent information. An additional notifi-cation will be made if specific actions are determined to be required.
Description of Circumstances
- In 1982 Indian Point Station Unit 3 had a leak at weld No. 6 on one of theirsteam generators (see Information Notice 82-37). Weld No. 6 is a full-penetration circumferential weld located in the transition zone betweenthe tube bundle and steam dryer areas, below the feedwater nozzles, andsubject to thermal cycling. The crack was started by corrosion and operatingtemperature fluctuations caused it to grow through the wall because of low-cyclefatigue. The repair method reduced the defects to an acceptable level.Ultrasonic examinations have been performed during outages since 1982 and inthe summer of 1985. Previously known indications that appear to have grown insize are being evaluated.In 1983 Surry Power Station Unit 2 performed ultrasonic examinations of theNo. 6 welds. The original construction weld at Unit 2 is 6 inches above theweld that attached the lower portion of all three replacement steam generatorsin 1980 (see attached sketch). The examination showed widespread indicationsof discontinuities on the inside surface of this weld in the "A" steam genera-tor. None of the indications seemed large enough to be rejected and it was8507290456 IN 85-65July 31, 1985 decided that they were surface blemishes of reflections from weld geometry. InMarch 1985, an ultrasonic reexamination was performed on the original construc-tion weld at Surry and larger, but acceptable, discontinuities were found inthe same locations. The inside surface of the weld in generator A wasvisually examined, but no defects were seen. However, when magnetic particletesting was performed at the request of the NRC, closely spaced linear crackswere found over a large portion of the circumference. The appearance of thesecracks was similar to those at Indian Point. The safety significance is thatsubstantial loss of secondary coolant could occur without warning if crackingdegradation continued undetected.The cracks in generator A were in a narrow band at the upper edge of the weldand covered almost the entire inside diameter. The cracks were as deep as 1/2inch and were covered by the surface oxide, which obscured detection by visualexamination. Generators B and C had numerous, smaller, circumferential cracksin the same location. To complicate matters, there were 10 unacceptablesubsurface indications in generator B, based on the requirements of ASMESection XI, IWB-3511. After a fracture and fatigue evaluation, these subsur-face indications were accepted by ASME IWB-3600. The surface cracks in allthree generators were removed by grinding; repair welding was not necessary.Weld No. 6 was made on-site and had high residual stresses as a result of thelow preheat and postweld heat treatment temperatures. The steel in the vicini-ty of the weld pitted when the secondary water contained high oxygen concen-trations (higher than 25 ppb) and contaminants such as chlorides and copperions. In addition to internal pressure, this portion of the steam generatorhas a change in cross-section and undergoes thermal cycling. Heat treatment ofthe nearby replacement weld in 1980 reduced the residual stresses, but couldnot undo any existing damage to the original construction weld. The cracks ranfrom pit to pit and grew to an unacceptable size in less than one inspectionperiod.At the next outage, the No. 6 welds in all three steam generators at Surry Unit2 will be partially examined by magnetic particle testing. The subsurfaceindications in generator B also will be examined by ultrasonic methods. Slowgrowing corrosion cracks are irregular in length and depth. When the cracksare located in the fusion line between the weld and the base metal, evaluationis very difficult by ultrasonic methods alone. Magnetic particle testing ismore sensitive than visual examination and supplements ultrasonic examinationswhere there is a possibility of surface defects. ASME Section XI specifies themaximum allowable planar indications and the methods of examination, but thesemethods may not be sufficient to identify indications and defects in all cases.Additional surface preparation, calibration notches, personnel training, andsmaller ultrasonic probes may result in a better understanding of the ultrason-ic indications.
IN 85-65July 31, 1985 No specific action or written response is required by this information notice.If you have any questions about this matter, please contact the RegionalAdministrator of the appropriate regional office or this office.ar L. Jordan DirectorDivision of Eme gency Preparednessand Engineering ResponseOffice of Inspection and Enforcement
Technical Contact:
P. Cortland, IE(301) 492-4175Attachments:1. Sketch of Steam Generator2. List of Recently Issued IE Information Notices
Attachment 1IN 85-65July 31, 1985 Sketch Showing Steam Generator AORIGINALCONSTRUCTION6 N._- WELDN006/ 9980WELDTHAT ATTACHEDTHE REPLACEMENTSTEAM GENERATORS
Attachment 2IN 85-65July 31, 1985LIST OF RECENTLY ISSUEDIE INFORMATION NOTICESInformation Date ofNotice No. Subject Issue Issued to85-6485-63BBC Brown Boveri Low-VoltageK-Line Circuit Breakers, WithDeficient Overcurrent TripDevices Models OD-4 and 5Potential for Common-ModeFailure of Standby Gas Treat-ment System on Loss of Off-Site PowerBackup Telephone Numbers tothe NRC Operations Center7/26/857/25/857/23/8585-6285-6185-60Misadministrations to Patients 7/22/85Undergoing Thyroid ScansDefective Negative Pressure 7/17/85Air-Purifying, Fuel FacepieceRespiratorsValve Stem Corrosion Failures 7/17/85Failure Of A General Electric 7/17/85Type AK-2-25 Reactor TripBreakerAll power reactorfacilities holdingan OL or CPAll power reactorfacilities holdingan OL or CPAll power reactorfacilities holdingan OL and certainfuel facilitiesAll power reactorfacilities holdingan OL and certainfuel facilitiesAll power reactorfacilities holdingan OL or CPAll power reactorfacilities holdingan OL or CPAll power reactorfacilities designedby B&W and CE holdingan OL or CPAll power reactorfacilities holdingan OL or CP; fuelfacilities; andmaterial licenseesAll power reactorfacilities holdingan OL or CP85-5985-5885-57Lost Iridium-192 SourceResulting In The Death OfEight Persons In MoroccoInadequate EnvironmentControl For Components AndSystems In Extended StorageOr Layup7/16/857/15/8585-56OL = Operating LicenseCP = Construction Permit