United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 96-30: Inaccuracy of Diagnostic Equipment for Motor-Operated Butterfly Valves

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                            WASHINGTON, D.C.  20555

                                 May 21, 1996


NRC INFORMATION NOTICE 96-30:  INACCURACY OF DIAGNOSTIC EQUIPMENT FOR  
                               MOTOR-OPERATED BUTTERFLY VALVES


Addressees

All holders of operating licenses or construction permits for nuclear power
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the increased inaccuracy of certain diagnostic
equipment for measuring torque when operating butterfly valves.  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 are not
NRC requirements; therefore, no specific action or written response is
required.  

Background

In Generic Letter (GL) 89-10, "Safety-Related Motor-Operated Valve Testing and
Surveillance," the NRC staff requested that nuclear power plant licensees and
construction permit holders verify the design-basis capability of their
safety-related motor-operated valves (MOVs).  As an integral part of their MOV
programs, most licensees rely on diagnostic equipment to provide information
on the torque and thrust required to open and close valves, and the amount of
torque and thrust delivered by the motor actuator.  Various types of MOV
diagnostic equipment are available to estimate torque and thrust for gate,
globe, and butterfly valves.  Because some licensees make decisions regarding
the operability of safety-related MOVs on the basis of diagnostic equipment
readings, inaccuracies in MOV diagnostic equipment can adversely affect the
safe operation of a nuclear power plant.

On June 28, 1993, the NRC staff issued Supplement 5 to GL 89-10, "Inaccuracy
of Motor-Operated Valve Diagnostic Equipment," which discussed then-recent
information on the inaccuracy of MOV diagnostic equipment that raised a
generic concern regarding the reliability of data provided by certain MOV
diagnostic equipment.  In Supplement 5 to GL 89-10, the staff stated that the
MOV Users' Group of nuclear power plant licensees had released a report
indicating that the MOV diagnostic equipment that relied on spring pack
displacement to estimate stem thrust in gate and globe valves was less
accurate than its vendors claimed.  The staff also discussed greater-than-
assumed inaccuracy of MOV diagnostic equipment that relies on valve yoke
strain to estimate stem thrust in gate and globe valves.  As a result of the 


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                                                            May 21, 1996
                                                            Page 2 of 3


inaccuracy concerns for MOV diagnostic equipment used with gate and globe
valves, the staff (in Supplement 5 to GL 89-10) asked licensees to reexamine
their MOV programs and to report measures taken or planned to account for
uncertainties in properly setting valve operating thrust to ensure
operability.  The staff stated that licensees should not limit their
evaluations to only the specific examples of increased inaccuracy of MOV
diagnostic equipment discussed in Supplement 5, but should consider any
information reasonably available to them.  The staff reviewed the licensees'
responses to Supplement 5 to GL 89-10 and conducted additional evaluations
during GL 89-10 inspections.

Description of Circumstances

ITI MOVATS Incorporated developed the Butterfly Analysis and Review Test
(BART) System as a method for determining the torque output of Limitorque HBC
gear boxes equipped with Limitorque motor actuators on butterfly valves.  In
the BART System, a load cell is mounted between the HBC gearbox housing and
the HBC worm gear.  Actuator torque is determined by multiplying the force
resisted in the load cell by the length of the moment arm.  In MOVATS Users
Technical Notice (MUTN) 96-01 (dated April 1996), ITI MOVATS stated that the
inaccuracy of the BART System had been considered to be equal to the
inaccuracy of the load cell (plus or minus the sum of 2 percent of reading and
0.4 percent of full scale).  However, recent observations and questions
concerning the performance of the BART System under field conditions led ITI
MOVATS to perform testing to determine the inaccuracy of the system.  In MUTN
96-01, ITI MOVATS reports that its test program revealed the inaccuracy of the
various fixture sizes of the BART System to be as follows:

        Fixture Size                               Inaccuracy                 

      H0BC, H1BC, H2BC              +(14.0% of reading + 5.2% of full scale)
                                    -( 4.0% of reading + 1.0% of full scale)

      H3BC                          +(14.0% of reading + 746 foot-pounds)
                                    -(14.0% of reading + 311 foot-pounds)

ITI MOVATS notes that the effects of both torque switch repeatability and HBC
gear box repeatability are included in the new inaccuracy values.  The vendor
also states that these inaccuracy values are only valid for torque loads
between 20 percent and 100 percent of the full-load rating of the HBC gear
box.  ITI MOVATS offers no guidance in MUTN 96-01 for predicting inaccuracy
outside of this load range.

Discussion

The BART System is typically used to determine torque output at torque switch
trip when operating motor-operated butterfly valves under static (no flow)
conditions.  Overprediction of actual torque at the torque switch trip could
result in the motor actuator failing to fully stroke the valve under dynamic
flow conditions.  Underprediction of actual torque at the torque switch trip
could result in exceeding actuator or valve structural limits, or degraded-.                                                            IN 96-30
                                                            May 21, 1996
                                                            Page 3 of 3


voltage motor capability.  Depending on the use of the diagnostic system and
the control circuitry of the motor actuator, the operation of limit-switch-
controlled butterfly valves might also be adversely affected by the increased
inaccuracy of the BART System.

In MUTN 96-01, ITI MOVATS recommends that all quarter-turn valves that have
been set up using the BART System be reevaluated using the revised values for
inaccuracy.  The vendor also suggests that, when using the BART System of
sizes H0BC, H1BC, and H2BC, the open and close strokes should begin with the
load cell in the relaxed position to simplify determination of zero load. 
This information notice is being issued because valves that were marginally
operable assuming the old inaccuracy may be inoperable based on the new
inaccuracy.

Related Generic Communications

The staff has alerted the industry to concerns about inaccuracy regarding
other MOV diagnostic equipment.  For example, the staff issued Information
Notice (IN) 92-23, "Results of Validation Testing of Motor-Operated Valve
Diagnostic Equipment;" IN 93-01, "Accuracy of Motor-Operated Valve Diagnostic
Equipment Manufactured by Liberty Technologies;" and IN 94-18, "Accuracy of
Motor-Operated Valve Diagnostic Equipment (Responses to Supplement 5 to
GL 89-10)."

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 Office of
Nuclear Reactor Regulation (NRR) project manager.


                                          signed by

                                    Brian K. Grimes, Acting Director
                                    Division of Reactor Program Management
                                    Office of Nuclear Reactor Regulation

Technical contacts:  T. Scarbrough, NRR
                     (301) 415-2794
                     Internet:tgs@nrc.gov

                     M. Runyan, RIV
                     (817) 860-8142
                     Internet:mfr@nrc.gov
Page Last Reviewed/Updated Thursday, November 21, 2013