Information Notice No. 90-30: Ultrasonic Inspection Techniques for Dissimilar Metal Welds

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                                 May 1, 1990


Information Notice No. 90-30:  ULTRASONIC INSPECTION TECHNIQUES FOR 
                                   DISSIMILAR METAL WELDS


Addressees:

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose:

This information notice is intended to alert addressees to potential 
problems associated with the ultrasonic examination of dissimilar metal 
welds in operating nuclear plants.  It is expected that recipients will 
review the information for applicability to their facilities and consider 
actions, as appropriate, to avoid similar problems.  However, suggestions 
contained in this information notice do not constitute NRC requirements; 
therefore, no specific action or written response is required.

Description of Circumstances:

NRC inspections of inservice inspection activities at licensed facilities 
have revealed that dissimilar metal welds containing Inconel 600 series base 
materials, alloy 82 and 182 weld butter, and/or filler material are being 
examined with shear wave mode ultrasonic testing (UT) transducers.  As a 
result of the intergranular stress corrosion cracking (IGSCC) problems 
identified in piping at boiling water reactor (BWR) plants, the NRC staff, 
BWR owners, independent research institutes and vendors of UT equipment have 
discovered that exclusive use of shear wave transducers will not reliably 
detect cracks in dissimilar metal welds of this type.  General Electric has 
notified BWR owners about this problem by the issuance of a Nuclear Services 
Information Letter dated June 23, 1989 (SIL No. 455, Revision 1 and 
Supplement 1).  SIL No. 455 and Supplement 1 contained specific 
recommendations regarding the ultrasonic testing procedures for BWR owners 
to use as part of their inservice inspection program in performing 
ultrasonic examinations of dissimilar metal welds.  These recommendations 
stated the following:

     "The use of 45-degree and 60-degree refracted longitudinal waves for 
     crack detection and sizing in the alloy 182 material and the low alloy 
     material is essential.  This should be performed at a gain level such 
     that the small signals received from the inside surface, which is 
     sometimes referred to as an ID roll, are at approximately 10 percent of 
     full screen height.  Scanning should be performed with the sound beams 
     directed both 
     


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     axially and circumferentially.  A 45-degree shear wave also should be 
     used in examining the low alloy material after suspect indications are 
     detected with the refracted longitudinal wave search units.  These 
     techniques should be qualified and calibrated on a realistic mock-up of 
     the weld configuration which contains suitable reflectors in the areas 
     of concern."

The following list contains examples observed during NRC inspections, 
demonstrating the limitations of shear wave transducers.  Had such 
transducers been used exclusively, significant axial and circumferential 
cracking would have gone undetected in Inconel 182 alloy weld butter, filler 
material and Inconel 600 base material. 

1.   Axial Cracking

     At the Brunswick Steam Electric Plant before 1986, the licensee 
     performed manual examinations on both 28-inch recirculation 
     nozzle-to-safe-end welds.  Calibrations were performed on a basic 
     Section XI calibration block using 45-degree shear-wave search units.  
     At this point, no indications associated with IGSCC were recorded.

     During the March 1986 outage, examinations were performed using 
     45-degree and 60-degree, 1Mhz, refracted longitudinal (RL) wave search 
     units.  One indication oriented in the axial direction was recorded in 
     the Inconel butter material in each nozzle.  These indications were 
     confirmed with both 45-degree RL and 60-degree RL search units and 
     estimated to be approximately 15 percent of the wall thickness.  
     However, neither of these indications could be detected with subsequent 
     45-degree or 60-degree shear wave examination.

2.   Axial and Circumferential Crack

     At Brunswick before 1988, the licensee used shear wave search units to 
     examine core spray safe-end-to-nozzle welds.  No indications associated 
     with IGSCC were recorded.

     During the 1988 outage, the licensee used 45-degree and 60-degree 
     refracted longitudinal wave search units for examination.  One axial 
     planar indication, estimated to be 30 percent of wall thickness on one 
     of the safe-ends, and one circumferential, planar indication estimated 
     to be 60-percent of the wall thickness on the other were recorded.  
     These indications were seen with both 45-degree and 60-degree refracted 
     longitudinal wave search units.  Neither of these indications were seen 
     with the 45-degree shear wave search unit.

3.   Inconel Base Material Crack

     During the 1988 outage at Brunswick, the licensee used both 45-degree 
     and 60-degree shear wave search units to examine all the welds in the 
     safe-end thermal sleeve attachments of the 12-inch recirculation 
     system.  Calibrations were performed on a safe-end nozzle mock-up block 
     with notches located in the thermal sleeve area.  No evidence of 
     cracking was detected with the shear wave examination, even with a 
     scanning gain level of 14 to 29 dB over the calibration sensitivity.
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     During an examination of a safe-end-to-nozzle weld repair overlay using 
     45-degree and 60-degree refracted longitudinal wave search units, the 
     licensee detected a crack extending from the safe-end thermal sleeve 
     attachment weld.  The licensee then performed 45-degree and 31-degree 
     refracted longitudinal wave calibrations on the same mock-up block 
     notches that were previously used for the shear wave examinations, and 
     reexamined all of the thermal sleeve welds.  With these examinations, 
     the licensee detected cracking throughout the heat affected zone and 
     adjacent safe-end material of the safe-end thermal sleeve.  All 10 of 
     the safe-end thermal sleeve welds showed evidence of extensive 
     intermittent cracking, for 360 degrees, which was associated with 
     IGSCC.

4.   Pressurized Water Reactor (PWR) Facilities

     NRC inspections at the Oconee Nuclear Station in November and December 
     of 1989 revealed that all dissimilar metal welds were examined with 
     shear wave transducers.  This finding indicates that licensees for PWR 
     facilities may be using inadequate UT inspection techniques as well.

Discussion:

Because no formal instructions exist concerning the choice of transducers 
for PWR applications, licensees may wish to evaluate the types of materials 
involved in the dissimilar metal welds at their plants and the ultrasonic 
techniques and equipment used to examine these materials.  The American 
Society of Mechanical Engineers (ASME) Code does not delineate whether shear 
wave or refracted longitudinal wave transducers should be used when 
performing inservice inspections of dissimilar metal welds.  However, the 
intent of the ASME Code examination is to thoroughly examine the weld and 
the adjacent base material in the heat-affected zone.  Without the proper 
transducers these examinations may not detect rejectable indications in the 
reactor coolant pressure boundary.  Furthermore, enhanced inspection 
effectiveness can improve confidence in the soundness of welds for plant 
life extension efforts.

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate NRR project 
manager.




                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation

Technical Contacts:  J. L. Coley, RII
                     (404) 331-5584

                     R. A. Hermann, NRR
                     (301) 492-0911

Attachment:  List of Recently Issued NRC Information Notices
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