Information Notice No. 90-03: Malfunction of Borg-Warner Bolted Bonnet Check Valves Caused by Failure of the Swing Arm
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
January 23, 1990
Information Notice No. 90-03: MALFUNCTION OF BORG-WARNER BOLTED BONNET
CHECK VALVES CAUSED BY FAILURE OF THE
SWING ARM
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert addressees to the
potential malfunctioning of Borg-Warner bolted bonnet check valves caused by
failure of the swing arm. 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:
On May 31, 1989, a 4-inch 150 lb Borg-Warner bolted bonnet swing check valve
installed in the service water system at the Comanche Peak Steam Electric
Station (CPSES), Unit 1, exhibited excessive backleakage. This resulted
from separation of the disk from the swing arm which connects the disc and
stud assembly to the clevis. The swing arm's collar, which surrounds the
disc stud, fractured radially in two places. Indications of surface flaws
were also found in two other swing arms. The swing arms in question were
produced from a 17-4PH alloy in accordance with Aerospace Materials
Specification 5398A and were required to be heat treated to an H1100
condition per Military Specification MIL-H-6875.
Discussion:
The licensee for CPSES, Texas Utilities Electric Company (TU Electric), and
consultants performed evaluations of six swing arms removed from service;
these evaluations included visual examination and fractography, chemical
analysis, metallography, the effects of heat treatment, and non-destructive
examination. It was concluded that the failure of the swing arm was caused
by surface defects formed during the fabrication process. Other
deficiencies identified as contributing factors of the failure were
inadequate heat treatment, weld repairs, high residual stresses, and the
high chloride environment of the service water system.
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IN 90-03
January 23, 1990
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The failure mechanism was defined as preexisting surface and subsurface
casting defects which propagated under the influence of raw water and
residual stresses during normal operating conditions. TU Electric's
consultants concluded that the swing arm castings were of poor quality; they
exhibited hot cracks, porosity, weld repair, and inadequate heat treatment.
When some of these swing arms were solution annealed and aged to produce the
H1100 condition, the swing arms exhibited lower hardness. If the swing arms
had been properly heat treated, little or no change in hardness would have
been expected. As a result of these problems, TU Electric is purchasing
replacement swing arms produced from investment castings, rather than sand
castings. The consultants also recommended that additional examinations be
performed on the remaining swing arms, including a 10X visual examination,
dimensional inspection, liquid penetrant test, and replication. Using these
inspection and testing methods, 17 of 91 swing arms examined by TU Electric
were rejected.
An NRC inspection of BW/IP International, Incorporated, Vernon, California,
(formerly Borg-Warner Nuclear Valve Division of Van Nuys, California) was
performed from September 11-14, 1989. During the inspection, BW/IP could
not produce documentation to support the placing of companies on the list of
qualified suppliers for manufacture of the swing arms used in safety-related
check valves. Records reviewed indicated that the swing arm that failed in
service was manufactured by the Industrial Pattern and Casting Company and
was subsequently heat treated by the Valley Heat Treating Company. During
the inspection, it was determined that Valley Heat Treating Company was not
on the list of approved suppliers. In addition, the inspectors could not
determine from the records whether the failed swing arms were properly
solution annealed or heat treated, nor were the swing arms serialized for
traceability.
The inspectors also reviewed the replacement swing arms ordered by TU
Electric. TU Electric had imposed Appendix B of 10 CFR Part 50 and 10 CFR
Part 21 in the purchase order for the replacement swing arms and required a
certificate of conformance. During the inspection, it was determined that
eight swing arms sold as replacements to TU Electric had been transferred in
1986 from the Van Nuys plant to the Vernon plant. During this transfer the
records associated with the swing arms were apparently lost. Because BW/IP
did not have documentation to support this inventory as meeting
safety-related requirements, BW/IP decided to dedicate the swing arms for
use by performing a material identity check, and a visual and dimensional
verification. However, the NRC inspectors determined that BW/IP's
dedication was inadequate because the swing arms' primary critical
characteristics (mechanical and chemical properties) were not verified by
BW/IP. The method used by BW/IP was only capable of sorting generic alloy
groups such as austenitic and martensitic stainless steels, but could not
distinguish between the four typical martensitic specifications used by
BW/IP. In addition, the results of the visual inspection performed on the
arms were not documented.
The NRC concluded that Borg-Warner and BW/IP classified non-pressure
boundary valve internals as exempt under requirements of Section III of the
American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel
Code, failed
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IN 90-03
January 23, 1990
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to recognize that Appendix B to 10 CFR Part 50 was imposed and applicable to
the valve internals, and as a result did not impose nuclear quality
assurance requirements on the manufacturer of these parts. The swing arm
failure at the CPSES raises concerns about the quality of non-pressure
boundary items supplied by BW/IP for use in safety-related applications.
Documentation reviewed during the BW/IP inspection identified additional
weaknesses such as the placement of vendors on the approved vendors list
without an adequate basis and the use of ASME Quality System Certificate
holders without any evaluation of the suppliers' or manufacturers' quality
assurance program by BW/IP. This practice was contrary to BW/IP's
procedures. In one example, there was no documented basis to support
qualification of ACME Castings, Incorporated, which is currently furnishing
cast swing arms to BW/IP.
The subject of qualification and oversight of vendors and procurement of
non-pressure boundary parts has been discussed in NRC Information Notice (IN)
88-95, "Inadequate Procurement Requirements Imposed By Licensees On
Vendors," and IN 86-21, "Recognition of ASME Accreditation Program For N
Stamp Holders."
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: R. L. Pettis, NRR
(301) 492-3214
M. R. Snodderly, NRR
(301) 492-0978
Attachment: List of Recently Issued NRC Information Notices
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