Information Notice No. 89-61: Failure of Borg-Warner Gate Valves to Close Against Differential Pressure
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
August 30, 1989
Information Notice No. 89-61: FAILURE OF BORG-WARNER GATE VALVES TO
CLOSE AGAINST DIFFERENTIAL PRESSURE
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
resulting from Borg-Warner gate valves with air or motor actuators failing to
close against differential pressures. 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 March 14, 1988, a motor-driven auxiliary feedwater (AFW) pump discharge
isolation motor-operated valve (MOV) failed to fully close against a differen-
tial pressure of 1800 psi at Catawba Nuclear Power Plant, Unit 2. The valve
failed while an AFW piping flush was being performed. At the time of the
failure, the reactor was shut down and the steam generators were in hot
standby. The failure of the MOV to fully close was a contributing factor that
led to overfilling steam generator 2A and resulted in an automatic feedwater
isolation. The licensee, Duke Power Company, investigated the failure and
reported (Licensee Event Report No. 414/89-10) the cause to be a higher valve
factor than originally specified by the valve manufacturer, Borg-Warner, for
sizing valve actuators. The valve factor is the term which is multiplied by
the valve seat area and the differential pressure across the valve to
calculate one of the parameters used in the standard valve thrust formula. If
a low valve factor is used when sizing the valve air or motor actuator, the
calculated required valve thrust will also be low. This results in low torque
switch settings being specified and, in some cases, can result in undersized
air or motor actuators.
Discussion:
The AFW MOV that failed to close against 1800 psi, 2CA62A, was a Borg-Warner
4-inch, 1500-psi, flexible wedge, carbon steel gate valve with a pinned body
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August 30, 1989
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guide insert ring disk guide. Actuation of the torque switch stops the motor
when the valve is closed and fully seated. The torque switch was not bypassed
in the closing direction. Following the March 14, 1988, failure to close, the
valve was diagnostically tested and the switch settings were found to be
within specified tolerances. Since no problems were found with the torque
switch settings, the valve was retested at 1800 psi differential pressure and
again failed to fully close. In order to get the valve to fully close at 1800
psi differential pressure, the closed torque switch setting had to be
increased to the maximum allowed by the manufacturer's design calculations.
During the subsequent refueling outage, the valve was disassembled and
inspected by the licensee in order to determine what was creating the
excessive friction between the disk and seat rings. The inspection did not
reveal any damage or conditions that would have caused excessive friction.
In November 1988, Duke Power Company performed differential pressure testing
on an MOV identical in design to 2CA62A. This testing was performed on a test
loop at the Riverbend Steam Station. During the testing, valve signature
analysis was obtained. This testing resulted in higher than anticipated
seating loads at high differential pressure conditions, and the valve failed
to close on two of the tests completed with differential pressures greater
than 1500 psi.
In November 1988, four Catawba Nuclear Power Plant Unit 1 AFW MOVs, identical
in design and size to 2CA62A, were differential pressure tested at 1800 psi.
All four valves indicated intermediate position after being closed during the
test and were 1/8 inch to 1/2 inch from the fully closed position. The test
results identified that all four valves failed to wedge completely shut. One
valve did not close enough to shut off flow.
In March 1989, valve 2CA62A and three identical Unit 2 AFW MOVs were differen-
tial pressure tested at 1800 psi. During the test, the three Unit 2 identical
valves failed to completely close and isolate flow. All four valves failed to
wedge completely shut. Valve signature analysis test data obtained during
this testing yielded closing valve factors ranging from 0.38 to 0.74 and were
different for each valve tested. These were higher than the 0.3 valve factor
utilized by the valve manufacturer to size the actuators.
Testing performed by Duke Power Company on carbon steel valves similar in
design to 2CA62A has yielded opening valve factors ranging from 0.48 to 0.67.
Testing performed by Duke Power Company on stainless steel valves similar to
2CA62A has yielded valve factors ranging from slightly higher than 0.3 to 0.5.
Based on Duke Power Company testing, the valve factor of 0.3 originally uti-
lized for Borg-Warner flexible wedge carbon steel or stainless steel gate
valves with pinned body guide insert rings when sizing air or motor actuators
was not correct. The actual valve factors, as measured by Duke Power Company,
vary from valve to valve but are consistently above 0.3. This results in the
potential that air- or motor-actuated valves will not operate against a
differential pressure when called upon to do so because of inadequate torque
switch settings or undersized actuators.
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August 30, 1989
Page 3 of 3
Related Generic Communications:
The general concern of the ability of motor-operated valves to function
properly when subjected to the design basis loadings has been previously
addressed in NRC Bulletins 81-02, "Failure of Gate Type Valves to Close
Against Differential Pressure," and 85-03, "Motor-Operated Valve Common Mode
Failures During Plant Transients Due to Improper Switch Settings;" Circular
77-01, "Malfunctions of Limitorque Valve Operators;" Information Notices
81-31, "Failure of Safety Injection Valves to Operate Against Differential
Pressure," and 85-50, "Complete Loss of Main and Auxiliary Feedwater at a PWR
Designed by Babcock & Wilcox;" and Generic Letter 89-10, "Safety-Related
Motor-Operated Valve Testing and Surveillance."
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: S. Tingen, RII
(404) 331-2603
Attachment: List of Recently Issued NRC Information Notices
. Attachment
IN 89-61
August 30, 1989
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
______________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to_________
88-48, Licensee Report of Defective 8/22/89 All holders of OLs
Supp. 2 Refurbished Valves or CPs for nuclear
power reactors.
89-60 Maintenance of Teletherapy 8/18/89 All NRC Medical
Units Teletherapy
Licensees.
89-59 Suppliers of Potentially 8/16/89 All holders of OLs
Misrepresented Fasteners or CPs for nuclear
power reactors.
89-58 Disablement of Turbine-Driven 8/3/89 All holders of OLs
Auxiliary Feedwater Pump Due or CPs for PWRs.
to Closure of One of the
Parallel Steam Supply Valves
89-57 Unqualified Electrical 7/26/89 All holders of OLs
Splices in Vendor-Supplied or CPs for nuclear
Environmentally Qualified power reactors.
Equipment
89-56 Questionable Certification 7/20/89 All holders of OLs
of Material Supplied to the or CPs for nuclear
Defense Department by Nuclear power reactors.
Suppliers
89-45, Metalclad, Low-Voltage 7/6/89 All holders of OLs
Supp. 1 Power Circuit Breakers or CPs for nuclear
Refurbished With Substandard power reactors.
Parts
89-55 Degradation of Containment 6/30/89 All holders of OLs
Isolation Capability by a or CPs for nuclear
High-Energy Line Break power reactors.
89-54 Potential Overpressurization 6/23/89 All holders of OLs
of the Component Cooling or CPs for nuclear
Water System power reactors.
89-53 Rupture of Extraction 6/13/89 All holders of OLs
Steam Line on High or CPs for nuclear
Pressure Turbine power reactors.
______________________________________________________________________________
OL = Operating License
CP = Construction Permit
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