Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
May 15, 1991
Information Notice No. 91-32: POSSIBLE FLAWS IN CERTAIN PIPING
SYSTEMS FABRICATED BY ASSOCIATED PIPING
AND ENGINEERING
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is intended to alert addressees to possible flaws in
certain piping systems fabricated by Associated Piping and Engineering
(AP&E), Compton, California. 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:
During inservice inspection (ISI) in the January 1991 outage at the Hope
Creek facility, the licensee detected cracks with liquid penetrant
examination (PT) techniques on the outside diameter surface of two
28-inch-diameter by 1.35- to 1.40-inch wall butt welds. The welds were
located in loops A and B of the type 304 stainless steel recirculation
piping system. The licensee found three indications of lengths ranging from
1 1/2 inches to 7 1/2 inches. These indications were circumferentially
oriented and were located approximately in the center of the weld. The
welds, which coincidentally were the same welds in both loops, were
fabricated as shop welds by AP&E in 1980. The records showed that the spool
pieces were solution annealed after welding at 1925 to 1960 degrees F
followed by water quenching. The subject welds were reportedly made using
the gas tungsten arc welding process for the root pass, followed by a cover
pass deposited by the manual metal arc process, with subsequent fill layers
deposited by an automatic submerged arc (flux/wire) process.
After light grinding failed to remove the defects, the licensee completely
removed indications from both welds by excavating the areas to a depth of
7/16 inch (32 percent of wall thickness). Before excavation, the licensee
removed a 1/4-inch-wide by 1 1/2-inch-long boat sample for metallurgical
examination. The examination indicated that the defect was a hot short
crack, a welding defect typically found in stainless steel welds. The
cracks apparently
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IN 91-32
May 15, 1991
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developed during the submerged arc process because of the low ferrite level
(0.1 to 1.9 percent) that was found in the boat sample even though certified
test reports of the filler materials used by AP&E showed a ferrite level of
6 to 12 percent. (A minimum ferrite content of 5 percent in a deposited
austenitic weld metal is usually specified to avoid weld metal cracking.)
The examination also indicated no evidence of propagation during the
solution anneal process or by some corrosion or fatigue mechanism during
subsequent service.
The licensee for Hope Creek reported that a review of the fabrication nonde-
structive examination (NDE) record showed no reportable PT indications and
no rejectable radiographic indications. The licensee also reported that the
defects were not detected by the ISI ultrasonic testing (UT) specified in
Section XI of the current American Society of Mechanical Engineering (ASME)
Standards principally because the UT method used (shear wave) is designed to
find intergranular stress corrosion cracking (IGSCC) on the inside diameter
surface as well as flaws in the bottom third of the weld. The hot short
cracks in this case were found in the upper third of the weld.
To determine the extent of the problem and to ensure integrity of the
recirculation piping system, the licensee proceeded to perform PT on all 36
similar welds (100 percent) in the recirculation system. No other
rejectable indication was found. The licensee also performed UT on eight
additional welds (five 28-inch-diameter and three 12-inch-diameter pipes)
using a high-angle longitudinal refractive wave method. The method was
validated to find defects in the upper third (near the outer surface of the
weld) with a mock-up furnished by the Electric Power Research Institute
(EPRI) that contained weld defects similar to and at the same level as those
found in the recirculation piping welds. The licensee found no rejectable
indications in any of the eight welds.
Discussion:
The cracks found during the ISI activities at Hope Creek in 1991 were not
detected by pre-service inspection and are different from the IGSCC
associated with welds in large-diameter stainless steel piping. IGSCC is
found in the heat-affected zone at the pipe's inner surface in the base
metal adjacent to the fusion line. The cracks in the Hope Creek case were
found at the pipe welds' outer surfaces in the upper third of the weld and
were caused during fabrication by a "hot short" cracking mechanism. The NRC
has not identified any similar problems at other facilities. However, since
the piping manufacturer, AP&E, is out of business, notice of defective welds
manufactured by this company may not have been disseminated properly to
potentially affected facilities.
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IN 91-32
May 15, 1991
Page 3 of 3
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: David E. Smith, NRR
(301) 492-0711
Herbert J. Kaplan, RI
(215) 337-5346
Attachment: List of Recently Issued NRC Information Notices
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