Information Notice 1990-30, Ultrasonic Inspection Techniques for Dissimilar Metal Welds
| ML031470652 | |
| Person / Time | |
|---|---|
| Issue date: | 05/01/1999 |
| From: | Rossi C Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| IN-90-030 | |
| Download: ML031470652 (3) | |
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Home > Electronic Reading Room > Document Collections > General Communications > Information Notices > 1990 > IN 9 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
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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Information Notice No. 90-30: 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, lMhz, 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.
May 1, 1990 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
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Information Notice No. 90-30: 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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