United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 85-65: Crack Growth in Steam Generator Girth Welds

                                                            SSINS No.: 6835 
                                                            IN 85-65       

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555

                                July 31, 1985


Information Notice No. 85-65:   CRACK GROWTH IN STEAM GENERATOR GIRTH 
                                   WELDS 

Addressees: 

All nuclear power pressurized water reactor (PWR) facilities holding an 
operating license (OL) or a construction permit (CP). 

Purpose: 

This information notice is provided to alert recipients of a potentially 
significant problem pertaining to the growth in indications in steam 
generator circumferential welds. Ultrasonic examination had determined 
previously that the welds were acceptable. It is suggested that recipients 
review the information for applicability to their facilities and consider 
actions, if appropriate, to preclude a similar problem occurring at their 
facilities. However, suggestions contained in this information notice do not
constitute NRC requirements; therefore, no specific action or written 
response is required. 

The NRC is continuing to evaluate pertinent information. An additional 
notification 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 their
steam generators (see Information Notice 82-37). Weld No. 6 is a full-
penetration circumferential weld located in the transition zone between the 
tube bundle and steam dryer areas, below the feedwater nozzles, and subject 
to thermal cycling. The crack was started by corrosion and operating 
temperature fluctuations caused it to grow through the wall because of 
low-cycle fatigue. The repair method reduced the defects to an acceptable 
level. Ultrasonic examinations have been performed during outages since 1982
and in the summer of 1985. Previously known indications that appear to have 
grown in size are being evaluated. 

In 1983 Surry Power Station Unit 2 performed ultrasonic examinations of the 
No. 6 welds. The original construction weld at Unit 2 is 6 inches above the 
weld that attached the lower portion of all three replacement steam 
generators in 1980 (see attached sketch). The examination showed widespread 
indications of discontinuities on the inside surface of this weld in the "A"
steam generator. None of the indications seemed large enough to be rejected 
and it was 

8507290456 
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                                                             IN 85-65     
                                                             July 31, 1985 
                                                             Page 2 of 3  

decided that they were surface blemishes of reflections from weld geometry. 
In March 1985, an ultrasonic reexamination was performed on the original 
construction weld at Surry and larger, but acceptable, discontinuities were 
found in the same locations. The inside surface of the weld in generator A 
was visually examined, but no defects were seen. However, when magnetic 
particle testing was performed at the request of the NRC, closely spaced 
linear cracks were found over a large portion of the circumference. The 
appearance of these cracks was similar to those at Indian Point. The safety 
significance is that substantial loss of secondary coolant could occur 
without warning if cracking degradation continued undetected. 

The cracks in generator A were in a narrow band at the upper edge of the 
weld and covered almost the entire inside diameter. The cracks were as deep 
as 1/2 inch and were covered by the surface oxide, which obscured detection 
by visual examination. Generators B and C had numerous, smaller, 
circumferential cracks in the same location. To complicate matters, there 
were 10 unacceptable subsurface indications in generator B, based on the 
requirements of ASME Section XI, IWB-3511. After a fracture and fatigue 
evaluation, these subsurface indications were accepted by ASME IWB-3600. The 
surface cracks in all three 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 
the low preheat and postweld heat treatment temperatures. The steel in the 
vicinity of the weld pitted when the secondary water contained high oxygen 
concentrations (higher than 25 ppb) and contaminants such as chlorides and 
copper ions. In addition to internal pressure, this portion of the steam 
generator has a change in cross-section and undergoes thermal cycling. Heat 
treatment of the nearby replacement weld in 1980 reduced the residual 
stresses, but could not undo any existing damage to the original 
construction weld. The cracks ran from pit to pit and grew to an 
unacceptable size in less than one inspection period. 

At the next outage, the No. 6 welds in all three steam generators at Surry 
Unit 2 will be partially examined by magnetic particle testing. The 
subsurface indications in generator B also will be examined by ultrasonic 
methods. Slow growing corrosion cracks are irregular in length and depth. 
When the cracks are located in the fusion line between the weld and the base
metal, evaluation is very difficult by ultrasonic methods alone. Magnetic 
particle testing is more sensitive than visual examination and supplements 
ultrasonic examinations where there is a possibility of surface defects. 
ASME Section XI specifies the maximum allowable planar indications and the 
methods of examination, but these methods may not be sufficient to identify 
indications and defects in all cases. Additional surface preparation, 
calibration notches, personnel training, and smaller ultrasonic probes may 
result in a better understanding of the ultrasonic indications. 
.

                                                             IN 85-65     
                                                             July 31, 1985 
                                                             Page 3 of 3  

No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or this office. 


                                   Edward L. Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  P. Cortland, IE
                    (301) 492-4175

Attachments:
1.   Sketch of Steam Generator
2.   List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, November 12, 2013