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

Motor-Operated Valve Performance Issues

ML031060093
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
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

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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 Chuck Hsu. AEOD

(301) 415-2794 (301) 415-6356 Email: tgs@nrc.gov 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 Recordkeeping, Decommis- 08/19/96 All U.S. Nuclear Regulatory

sioning Notifications for Commission licensees

Disposals of Radioactive

Waste by Land Burial

Authorized Under Former

10 CFR 20.304. 20.302.

and Current 20.2002

96-46 Zinc Plating of Hardened 08/12/96 All holders of OLs or CPs

Metal Parts and Removal for nuclear power reactors

of Protective Coatings

in Refurbished Circuit

Breakers

96-45 Potential Common-Mode 8/12/96 All holders of OLs or CPs

Post-Accident Failure of for nuclear power reactors

Containment Coolers

96-44 Failure of Reactor 8/05/96 All holders of OLs or CPs

Trip Breaker from Cracking for nuclear power reactors

of Phenolic Material in

secondary contact assembly

96-43 Failures of General 08/02/96 All holders of OLs or CPs

Electric Magne-Blast for nuclear power reactors

Circuit Breakers

96-42 Unexpected Opening of 08/05/96 All holders of OLs or CPs

Multiple Safety Relief for nuclear power reactors

Valves

96-41 Effects of a Decrease in 07/26/96 All holders of OLs or CPs

Feedwater Temperature on for pressurized water

Nuclear Instrumentation reactors

96-40 Deficiencies in Material 07/25/96 All holders of OLs or CPs

Dedication and Procurement for nuclear power reactors

Practices and in Audits of

Vendors

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.

'Itiinal signed byBrian K Gimes

41116A-Thomas T. Martin. Director

I Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Thomas G. Scarbrough. NRR Chuck Hsu, AEOD

(301) 415-2794 (301) 415-6356 Email: tgs@nrc.gov 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

DOCUMENT NAME: 96-48.IN

To rpecefe a rrw of this document. Indicate In the box: "C" = Copy without enclosures "" WCopy Ores No copy

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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 Chuck Hsu, AEOD

(301) 415-2794 (301) 415-6356 Internet:tgs@nrc.gov 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 v r

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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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