United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 91-32: Possible Flaws in Certain Piping Systems Fabricated by Associated Piping and Engineering

                                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
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                                                            Page 2 of 3


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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