Information Notice 1996-48, Motor-Operated Valve Performance Issues

Motor-Operated Valve Performance Issues

ML031060093
Person / Time
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Issue date:	08/21/1996
From:	Martin T Office of Nuclear Reactor Regulation
To:
References
IN-96-048, NUDOCS 9608150028
Download: ML031060093 (13)

l UNITED STATES NUCLEAR REGULATORY

COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 August 21, 1996 NRC INFORMATION

NOTICE 96-48: MOTOR-OPERATED

VALVE PERFORMANCE

ISSUES

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 (1) lessons learned from the Electric Power Research Institute (EPRI) Motor-Operated

Valve (MOV) Performance

Prediction

Program, (2) performance

problems with MOV key failures described

in a recent NRC Office for Analysis and Evaluation

of Operational

Data (AEOD) study, and (3) the potential

for torque output from MOV actuators

to be less than predicted

by Limitorque

Corporation.

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 the 1980s. continuing

problems with the performance

of MOVs at nuclear power plants raised concerns regarding

MOV design, testing, and maintenance.

In response to these problems, both the nuclear industry and NRC initiated efforts to improve the performance

of MOVs at nuclear plants. In 1989, the NRC staff issued Generic Letter (GL) 89-10, "Safety-Related

Motor-Operated

Valve Testing and Surveillance," requesting

that nuclear power plant licensees and construction

permit holders verify the design-basis

capability

of their safety-related

MOVs. In response to GL 89-10, the nuclear industry has studied the performance

of MOVs through testing and analyses.

As a result of these activities, some weaknesses

in the design and manufacture

of MOVs were discovered

through evaluation

of the performance

history of MOVs. In this information

notice, the staff discusses

three issues involving

MOV performance

that have been identified.

Description

of Circumstances

1. Lessons Learned from EPRI MOV Performance

Prediction

Program As part of the industry effort regarding

the MOV issue. EPRI initiated

an MOV Performance

Prediction

Program to develop a methodology

to be used by licensees

in demonstrating

the design-basis

capability

of MOVs when valve-specific design-basis

test data are not available.

The program included 9608150028 I PX 4\\\s 1-Dv-11C/if

IN 96-48 August 21, 1996 development

of improved methods for prediction

or evaluation

of system flow parameters;

gate, globe, and butterfly

valve performance:

and motor actuator rate-of-loading

effects (load-sensitive

behavior).

Further, EPRI performed testing to provide information

for refining the gate valve model and rate-of-loading methods and conducted

numerous MOV tests to provide data for model and method development

and validation, including

flow loop testing, parametric

flow loop testing of butterfly

valve disk designs, and in situ MOV testing.In November 1994, the Nuclear Energy Institute (NEI) submitted

the proprietary

EPRI Topical Report TR-103237, "EPRI MOV Performance

Prediction

Program -Topical Report," for review by the NRC staff. EPRI prepared 25 additional

reports to support the topical report. On March 15, 1996, the NRC staff issued a Safety Evaluation (SE) documenting

the staff review of the topical report. With the conditions

and limitations

described

in the SE, the staff stated that the EPRI program provides an acceptable

methodology

to predict the thrust or torque required to operate gate, globe, and butterfly

valves within the scope of the EPRI program and to bound the effects of load-sensitive

behavior on motor actuator thrust output.In a letter dated September

27, 1995, NEI forwarded

a summary of important contributions

and findings resulting

from the EPRI MOV Performance

Prediction

Program. As described

in an enclosure

to the NEI letter, important

findings (or confirmatory

information)

from the EPRI MOV program include the following:

a. The traditional

methods for predicting

gate valve performance

might be nonconservative

for many applications

because of incomplete

equations.

design features, manufacturing

controls, and wide-ranging

friction coefficients.

b. The edge radii on disk seats and guide slots are critical to gate valve performance

and predictability.

c. Stellite friction coefficients

increase with differential-pressure

valve strokes in cold water to a plateau level, stabilize

quickly in hot water, and decrease as differential

pressure increases.

d. Gate valves with carbon steel guides and disk guide slots with tight clearances

might fail to close under blowdown conditions.

e. Many existing gate valve manufacturing

and design processes

and controls, and plant maintenance

practices, might contribute

to poor valve performance.

f. Traditional

methods for predicting

globe valve performance

for incompressible

flow conditions

are nonconservative

for globe valves in which differential

pressure acts across the plug guide.

' IN 96-48 August 21. 1996 g. Globe valve thrust requirements

for some designs can be excessive

under compressible

flow and blowdown conditions

because of the potential

for plug-side

loading.h. Rate-of-loading

effects (load-sensitive

behavior)

can reduce the static thrust output by up to 30 percent under dynamic conditions.

i. Hydrodynamic

torque coefficients

used by some butterfly

valve manufacturers

might be nonconservative

for certain applications, with valves located near piping elbows especially

vulnerable.

j. Butterfly

valve seats should be periodically

replaced to avoid hardening or degradation.

In addition to these reported important

findings, EPRI confirmed

that thrust requirements

to unwedge a gate valve can be higher under dynamic conditions

than under static conditions.

2. MOV Key Failures On March 29. 1996. AEOD issued report AEOD/E96-01.

entitled, "Engineering

Evaluation

-Motor-Operated

Valve Key Failures," on the continuing

occurrence

of problems with keys in MOVs at nuclear power plants. A significant

number of MOV key failures have been identified

that involved (a) anti-rotation

keys.(b) valve operator-to-valve

stem keys. and (c) motor pinion gear keys. A total of 73 reports were written involving

MOV key failures between January 1990 through September

1995. Many of these key failures were not detected during surveillance

tests but were detected on demand, during valve operations.

or during maintenance

activities

and had existed for some time before they were discovered.

A number of key failures were discovered

during maintenance

activities

even though the valves had been operated satisfactorily

and passed all previous surveillance

tests.3. Limitorque

Motor Actuator Performance

In 1977. Limitorque

Corporation

established

guidelines (referred

to as the SEL documents)

for sizing ac-powered

motor actuators

used in MOVs. Those guidelines

predicted

the motor actuator output torque as a product of the nominal motor-rated

start torque. pullout efficiency, application

factor (typically

0.9), overall actuator gear ratio, and a degraded voltage factor.Over the past few years, Limitorque

has accepted the use of run efficiency

for closing valves powered by ac-powered

motor actuators.

Limitorque

has also stated that licensees

may eliminate

the application

factor when voltage supplied to the motor is less than 90 percent of its rated voltage. (See Limitorque

Technical

Update 93-03 [Accession

9608120083].)

Recent industry

IN 96-48 August 21. 1996 and NRC-sponsored

test information

has raised questions

regarding

the accuracy of the Limitorque

assumptions

for actuator efficiency.

Discussion

1. Lessons Learned from the EPRI MOV Performance

Prediction

Program As discussed

in the staff SE on the EPRI topical report, the EPRI program provided important

information

on the design, testing. and maintenance

of MOVs in nuclear power plants. Some of the EPRI information

is applicable

to gate.globe, and butterfly

valves regardless

of the type of actuator operating

the valve. Examples of such information

are given below: Gate Valves Almost all flow testing by licensees

in response to GL 89-10 was conducted under pumped-flow

conditions.

Several gate valves tested by EPRI under blowdown conditions

demonstrated

unpredictable

performance

and internal damage. Extrapolation

of test data from pumped-flow

conditions

to blowdown conditions

may not be sufficient

to ensure that a gate valve can operate under its design-basis

conditions.

Valve aging conditions

can influence

gate valve performance.

The thrust requirements

to operate gate valves under normal flow conditions

can increase with time and valve stroking.Thrust requirements

to unwedge gate valves under dynamic conditions

may be greater than under static conditions.

Globe Valves Limited testing by EPRI of globe valves under blowdown or high-temperature

flow conditions

suggested

that higher thrust than typically

predicted

may be required to operate these valves.Thrust requirements

for globe valves are influenced

by the area of the valve seat or guide. depending

on the valve design.The EPRI test database is not sufficient

to justify modifying

the Limitorque

guidelines

for sizing and setting globe valves to lower the typical valve factor of 1.1 as-umed in the guidelines.

k\ -#IN 96-48 August 21, 1996 Butterfly

Valves Several areas of the EPRI Butterfly

Valve Application

Guide need improvement

or correction.

EPRI is currently

revising the application

guide and plans to include new information

on flow and torque coefficients;

system analysis techniques;

treatment

of bearing, packing, and hub-seal torque: upstream elbow modeling:

and rated and survivable

torque calculations.

2. MOV Key Failures The MOV key failures may involve a common-cause

failure that could render redundant

trains of certain safety-related

systems inoperable

if they had remained undetected.

The MOV key failures can be attributed

to (a) instal-lation and design deficiencies

for anti-rotation

keys, (b) loosening

or slipping, wear or normal aging, excessive

force or overtorque, and discre-pancies in material or size for valve operator-to-valve

stem keys, and (c)high-impact

loads, improper materials, installation

deficiency, wear or normal aging, and vibration

for motor pinion gear keys.The anti-rotation

key failures involving

installation

deficiencies

were generally

associated

with inadequate

staking and securing of setscrews

during installation

of the keys. It appeared that the installation

instructions

provided by the vendors were not always included in licensee maintenance

procedures.

Many motor pinion gear key failures involving

an installation

deficiency

were due to failure to stake the keys following

replacement

of the motors or the pinion gears. Although licensees

revised their MOV maintenance

procedures

to include restaking

the pinion key or motor shaft as recommended

by Limitorque

Maintenance

Update 89-1 (Accession

9608120068), many licensees

did not investigate

the potential

problems of maintenance

activities

that were conducted

before their procedure

changes.The motor pinion gear key failures attributable

to high-impact

loads or improper material appear to involve AISI (American

Iron and Steel Institute)

type 1018 keys in high-speed

and high-inertia

configurations.

The replacement

of 1018 keys with harder 4140 keys in some cases may lead to keyway deforma-tion or damage, depending

on impact loads and the shaft material.

The situa-tion may present a complex stress problem that is not completely

considered

in design and could produce a severe and complex stress concentration

on the key, as well as the keyway. This situation

could lead to cracking and failure of the shaft.The potential

for these key problems to render safety systems inoperable

empa-sizes (a) the importance

of plant maintenance

programs in assuring that MOV keys are staked and secured as required, (b) the importance

of plant MOV surveillance

and maintenance

activities

in the early detection

of key

IN 96-48 August 21, 1996 degradation, and (c) the possibility

of shaft cracking as a result of replacement

of 1018 keys with harder material when the replacement

will involve a relatively

soft shaft and high impact loads.3. Limitorque

Motor Actuator Performance

The NRC staff conducted

an inspection

at Limitorque

in May 1993 and reviewed the basis for its motor actuator sizing guidelines.

As discussed

in NRC Inspection

Report 99900100/93-01.

the staff found that the values for individual

parameters

assumed in the Limitorque

sizing equation were not determined

by testing but were founded primarily

on engineering

judgment.

The lack of significant

failure history of motor actuators

when using the Limitorque

sizing equation has been the primary basis for confidence

in the equation.

Licensee modifications

of the parameters

in the Limitorque

sizing guidelines

has the potential

to influence

performance.

Tests of MOVs under differential

pressure and flow conditions

performed

by licensees

in response to GL 89-10 have revealed that significantly

more torque and thrust are required to open and close many gate valves than predicted

by the valve vendors. This need for more torque than originally

believed has led licensees

to evaluate the Limitorque

motor actuator sizing guidelines

to determine

whether more torque output is available

from the motor actuators than was predicted

by the guidelines.

The Limitorque

sizing guidelines

have typically

been assumed to underestimate

the output torque capability

of motor actuators.

Therefore, some licensees

eliminate

the application

factor from the output torque equation and use run efficiency

for ac-powered

MOVs in the closing direction.

Further, some licensees

have asserted that motor torque greater than the nominal start rating may be assumed in the sizing guidelines

because motors typically

deliver more torque than their rating before they stall.In response to the questions

surrounding

the Limitorque

sizing equation, the NRC Office of Nuclear Regulatory

Research evaluated

the performance

of Limitorque

motor actuators

through testing at the Idaho ational Engineering

Laboratory (INEL). Preliminary

results of the INEL tests suggest that (1)motor output is greater than the nominal rating for many motors. (2) the actual output efficiency

may not reach "run" efficiency

for some Limitorque

actuators

and may drop below "pullout" efficiency

under high loads, (3) the torque loss under degraded voltage conditions

can be more severe for some ac motors than the typically

assumed square of the ratio of actual voltage to rated voltage, and (4) the torque loss under degraded voltage conditions

can be more severe for some dc motors than the typically

assumed linear ratio.Preliminary

results of this testing are documented

in NUREG/CR-6100. "Gate Valve and Motor-Operator

Research Findings" (September

1995). INEL is preparing

a report. NUREG/CR-6478, to document its recent findings in this area. This report is scheduled

to be issued by the end of 1996.

IN 96-48 August 21, 1996 At meetings of the Motor-Operated

Valve Users' Group of nuclear power plant licensees

in February and July 1995, Commonwealth

Edison (ComEd) presented

the results of its motor and actuator output testing program. The testing conducted

by ComEd was more extensive

than the NRC-sponsored

testing and revealed similar results. Previously, in NUREG/CP-0137, "Proceedings

of the Third NRC/ASME Symposium

on Valve and Pump Testing" (July 1994), motor actuator testing by Texas Utilities

raised questions

regarding

Limitorque

motor actuator output. Texas Utilities

also found lower output during in situ motor actuator testing compared to torque stand testing.This information

raises concerns regarding

the basis for Limitorque

acceptance

of licensee assumptions

that the torque output of its actuators

is greater than predicted

by the original Limitorque

SEL guidelines.

The NRC staff has been discussing

with Limitorque

the discrepancy

between guidance relaxing the original motor actuator sizing criteria and the recent motor actuator test results. The manufacturer

has stated that updated information

for the industry on the sizing of its motor actuators

is being developed.

Related Generic Communications

• NRC IN 81-08. "Repetitive

Failures of Limitorque

Operator SMB-4 Motor-to-Shaft

Key," March 20, 1981 (Accession

8011040272).

• NRC IN 88-84. "Defective

Motor Shaft Keys in Limitorque

Motor Actuators." October 20, 1988 (Accession

8810140018).

• NRC GL 89-10, "Safety-Related

Motor-Operated

Valve Testing and Surveillance," June 28, 1989 (Accession

8906290082).

• NRC IN 90-37. "Sheared Pinion Gear-to-Shaft

Keys in Limitorque

Motor Actuators," May 24, 1990 (Accession

9005180095).

• NRC IN 90-40, "Results of NRC-Sponsored

Testing of Motor-Operated

Valves," June 5, 1990 (Accession

9005290270).

• NRC IN 93-42, "Failure of Anti-Rotation

Keys in Motor-Operated

Valves Manufactured

by Velan," June 9. 1993 (Accession

9306030147).

• NRC IN 93-88. "Status of Motor-Operated

Valve Performance

Prediction

Program by the Electric Power Research Institute," November 30, 1993 (Accession

93111904527!.

• NRC IN 94-10, "Failures

of Motor-Operated

Valve Electric Power Train Due to Sheared or Dislodged

Motor Pinion Gear Key," February 4. 1994 (Accession

9402010052).

IN 96-48 August 21, 1996

• NRC IN 94-69. "Potential

Inadequacies

in the Prediction

of Torque Requirements

for and Torque Output of Motor-Operated

Butterfly

Valves," September

28. 1994 (Accession

9409210211).

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.'. Thomas T. Martin, Director Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical

contacts: Thomas G. Scarbrough.

NRR (301) 415-2794 Email: tgs@nrc.gov

Chuck Hsu. AEOD (301) 415-6356 Email: cchl@nrc.gov

Michael T. Bugg, RIII (630) 829-9500 Email: mtb@nrc.gov

Attachment:

List of Recently Issued NRC Information

Notices A/; >'/c>

K>,0 Attachment

IN 96-48 August 21. 1996 LIST OF RECENTLY ISSUED NRC INFORMATION

NOTICES Information

Date of Notice No. Subject Issuance Issued to 96-47 96-46 96-45 96-44 96-43 Recordkeeping, Decommis-sioning Notifications

for Disposals

of Radioactive

Waste by Land Burial Authorized

Under Former 10 CFR 20.304. 20.302.and Current 20.2002 Zinc Plating of Hardened Metal Parts and Removal of Protective

Coatings in Refurbished

Circuit Breakers Potential

Common-Mode

Post-Accident

Failure of Containment

Coolers Failure of Reactor Trip Breaker from Cracking of Phenolic Material in secondary

contact assembly Failures of General Electric Magne-Blast

Circuit Breakers Unexpected

Opening of Multiple Safety Relief Valves Effects of a Decrease in Feedwater

Temperature

on Nuclear Instrumentation

Deficiencies

in Material Dedication

and Procurement

Practices

and in Audits of Vendors 08/19/96 08/12/96 8/12/96 8/05/96 08/02/96 08/05/96 07/26/96 07/25/96 All U.S. Nuclear Regulatory

Commission

licensees All holders of OLs or CPs for nuclear power reactors All holders of OLs or CPs for nuclear power reactors All holders of OLs or CPs for nuclear power reactors All holders of OLs or CPs for nuclear power reactors All holders of OLs or CPs for nuclear power reactors All holders of OLs or CPs for pressurized

water reactors All holders of OLs or CPs for nuclear power reactors 96-42 96-41 96-40 OL = Operating

License CP = Construction

Permit

IN 96-48 August 21, 1996

• NRC IN 94-69. "Potential

Inadequacies

in the Prediction

of Torque Requirements

for and Torque Output of Motor-Operated

Butterfly

Valves," September

28, 1994 (Accession

9409210211).

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.'I tiinal signed by Brian K Gimes 41116A-Thomas

T. Martin. Director I Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical

contacts: Thomas G. Scarbrough.

NRR (301) 415-2794 Email: tgs@nrc.gov

Chuck Hsu, AEOD (301) 415-6356 Email: cchl@nrc.gov

Michael T. Bugg. RIII (630) 829-9500 Email: mtb@nrc.gov

Attachment:

List of Recently Issued NRC Information

Notices*SEE PREVIOUS CONCURRENCE

"" W Copy Ores =N"- No copy DOCUMENT NAME: 96-48.IN To rpecefe a rrw of this document.

Indicate In the box: "C" = Copy without enclosures

OFFICE PUB:ADM I D/DE I C/PECB:DRPM

I ID INAME BCalure* BSheron* AChaffee*

J11M0rtin DATE 06/21/96 07/16/96 08/13/96 1 08//5n6 OFFICIAL RECORD COPY

IN 96-XX August XX. 1996 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.Brian K. Grimes. Acting Director Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical

contacts: Thomas G. Scarbrough.

NRR (301) 415-2794 Internet:tgs@nrc.gov

Chuck Hsu, AEOD (301) 415-6356 Internet:cchl@nrc.gov

Michael T. Bugg. NRR (630) 829-9500 Internet:mtb@nrc.gov

Attachment:

List of Recently Issued NRC Information

Notices*SEE PREVIOUS CONCURRENCE

Attachment:

List of Recently Issued NRC Information

Notices DOCUMENT NAME: G:\TAG\MOV96.IN5 Ta rgeAve a coov of this document.

Indicate In the box: "C" a Copy without enclosures

r -Copy with enclosures "N" z No copy OFFICE PUB:ADM -I D/DE I IC/PECB:DRPM;

l D/DRPM NAME BCalure* BSheronI ACha ffee VI BGrimes DATE 06/21/96 08/ /96 08/1';/96

-08/ /96 OFFICIAL PA f)v r -,r ' '.-

IN 96-XX July XX, 1996

• NRC IN 94-69, Potential

Inadequacies

in the Prediction

of Torque Requirements

for and Torque Output of Motor-Operated

Butterfly

Valves,w September

28, 1994.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.Brian K. Grimes, Acting Director Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical

contacts: Thomas G. Scarbrough, NRR (301) 415-2794 Internet:tgs~nrc.gov

Michael T. Bugg, NRR (301) 415-3303 Internet:mxbSnrc.gov

Chuck Hsu, AEOD (301) 415-6356 Internet:cchl@nrc.gov

Attachment:

List of Recently Issued NRC Information

Notices*SEE PREVIOUS CONCURRENCE

Afttthmontn

lit nf Pargnt1v TtvIs d NRC Informatinn

Notices OFFICE PUB:ADM D/ I 1&( \ C/PECB:DRPM

D/DRPM NAME BCalure* BS AChaffee BGrimes DATE 06/21/96 j /&/96 / /96 [ / /96 (OFFICIAL

RECORD COPY] $1 DOCUMENT NAME: G:\TAG\MOV96.INt

Chuck Hsu, AEOD (301) 415-6356 Internet:cchlnrc.gov

Attachment:

List of Recently Issued NRC Information

Notices OFFICE PUB:ADM C/E14EB:DE

C/PECB:DRPM

D/DRPM NAME Tech RWessman AChaffee BGrimes DATE C /LV//96 no /96 / /96 1 /96[OFFICIAL

RECORD COPY]DOCUMENT NAME: G:\TAG\MOV96.IN

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