Information Notice 1991-58, Dependency of Offset Disc Butterfly Valve'S Operation on Orientation with Respect to Flow

Dependency of Offset Disc Butterfly Valve'S Operation on Orientation with Respect to Flow

ML031190251
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, 05000371, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	09/20/1991
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-91-058, NUDOCS 9109160301
Download: ML031190251 (5)

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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 September 20, 1991 NRC INFORMATION NOTICE 91-58: DEPENDENCY OF OFFSET DISC BUTTERFLY VALVE'S

OPERATION ON ORIENTATION WITH RESPECT TO FLOW

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

The U.S. Nuclear Regulatory Commission is issuing this information notice to

alert addressees to the possibility that offset disc butterfly motor-operated

valves (MOV) may not function properly under design differential pressure and

flow conditions because the orientation of the valve to the direction of flow

can affect the operating characteristics of the valve. 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.

Description of Circumstances

On February 27, 1991, three service water MOVs that isolate .the recirculation

spray heat exchangers (RSHXs) at the North Anna Power Station, Unit 1, failed a

special test when they did not fully open on demand. The Virginia Electric and

Power Company (the licensee) was conducting the test under high flow and

differential pressure conditions to respond to NRC Generic Letter (GL) 89-10,

"Safety-Related Motor-Operated Valve Testing and Surveillance." The unit was

in cold shutdown for refueling when the failures occurred.

The valves are 16-inch, 150-pound offset disc butterfly MOVs. The licensee

determined that the valves had been installed in an orientation such that the

service water flow was toward the curved (shaft) side of the disc instead of

toward the flat side of the disc as intended (see Figure 1). This orientation

resulted in the need for a much higher torque than anticipated in order to open

the valves under the conditions established for the test.

Discussion

The licensee had recently performed modifications that reduced the torque

switch settings on the valves to values that ensured that the maximum torque

achieved would be within the actuator's rating. The licensee also calculated

9109160301 i Pot ItE D ql °s' 9IO%°

IN 91-58 September 20, 1991 the required torque values for the system application using the American Water

Works ssociation (AWWA) Standard for Rubber-Seated Butterfly Valves (C504-80).

The calculation indicated that the expected unseating torque was greater than

the dynamic torque (letter from W. L. Stewart, VEPCO, to NRC Document Control

Desk, "Reverse Installation.of Safety Related Motor Operated Offset Disc

Butterfly Valves," May.31)1991). Howeveir, the vendor-supplied valve coeffi- cients used in the calculation were for a disc of a different type than *that

installed, leading to an error in the calculation.

The affected MOVs are normally shut, and the intended safety function of the

valves is to open during an accident to supply cooling water to the RSHXs.

Under normal conditions, these valves should not experience significant flow or

differential pressure during the opening stroke because of another set of

isolation valves upstream. However, responding to Generic Letter 89-10, the

licensee developed a test to demonstrate that the valves could reopen under

worst-case flow and differential pressure conditions. On February 27, 1991, the licensee conducted theatests and challenged each valve individually to open

against a maximum differential pressure of approximately'75 pounds per square

inch (psid) and a maximum flow of approximately 9000 gallons per minute (gpm).

The three valves in question failed to fully open because the torque switches

opened at roughly mid-position. The licensee noted that the orientation of the

three failed valves was such that the service-water flowed toward the curved

(shaft) side of the disc (see Figure 1). Five other similar valves in the

system which were properly oriented with respect.to the service water flow were

tested successfully.

For this type of valve disc, when flow is toward the flat side of the disc, the

maximum torque on the opening stroke occurs during valve unseating, and the

actuator rating and torque switch setting should be selected to achieve this

torque. However,.if the service water flows toward the curved (shaft) side of

the disc, the hydrodynamic.torque developed as the flow increases acts against

the opening motion, and,.thus, a much higher actuator torque is required to

fully open the valve (see Figure 2). The actuators were not adequately sized

and rated for this situation, and the torque switches operated to prevent

damage to the actuators before the valves reached the fully open position.

The licensee indicated that the valves were probably installed correctly by the

architect/engineer with service water flow toward the flat side of the disc.

The licensee concluded that a lack of maintenance controls most likely caused

the reversal in the orientation. The licensee has also identified weaknesses

in the torque calculation method such-as poor modeling assumptions and a lack

of consideration of the differences between the coefficients for symmetrical

and offset discs.

The licensee removed the.three valves-and reversed them so that the service

water would flow toward the flat side of the disc. The licensee marked the

valves and the associated piping to indicate the direction of flow. Subsequent

testing of the valves was satisfactory. The licensee is also reviewing and

evaluating the models used for the service water system and the related

calculations.

KJ IN 91-58 September 20, 1991 If

This information notice requires no specific action or written response. contact one

you have any questions about the information in this notice, please

the appropriate Office of Nuclear

of the technical contacts listed below or

Reactor Regulation project manager.

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contacts: P. L. Campbell, NRR

(301) 492-1311 M. Lesser, RII

(703) 894-5421 Attachments:

1. Butterfly Valve Figures 1 and 2

2. List of Recently Issued NRC Information Notices: SAtA>,

I

Attachment 1 IN 91-58 September 20, 1991 ELW TOWARDS- FLOW TOWARDS

TH-ISK THE SHAF

_ ._s

Tvtolcel ODenina Torcues-lor-Offset OIsc-ButteaflV2alves

Curve a: off-set disc, Now towards sa

Curve b: off-set disA low towards disc

OPENING

TOROUE

Attachment 2 IN 91-58 September 20, 1991 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

91-57 Operational Experience 09/19/91 All holders of OLs or CPs

on Bus Transfers for nuclear power reactors.

91-56 Potential Radioactive 09/19/91 All holders of OLs or CPs

Leakage to Tank Vented for nuclear power reactors.

to Atmosphere

91-55 Failures Caused by An 09/16/91 All holders of OLs or CPs

Improperly Adjusted Test for nuclear power reactors.

Link In 4.16 KV General

Electric Switchgear

85-18, Failures of Undervoltage 09/10/91 All holders of OLs or CPs for

Supp. 1 Output Circuit Boards In Westinghouse (W)-designed

the Westinghouse-Designed nuclear power reactors.

Solid State Protection

System

91-54 Foreign Experience Regard- 09/06/91 All holders of OLs or CPs

ing Boron Dilution for pressurized water

reactors (PWRs).

89-90, Pressurizer Safety Valve 09/05/91 All holders of OLs or CPs

Supp. 2 Lift Setpoint Shift for nuclear power reactors.

91-53 Failure of Remote Shutdown 09/04/91 All holders of OLs or CPs

System Instrumentation for nuclear power reactors.

Because of Incorrectly

Installed Components

91-52 Nonconservative Errors 08/29/91 All holders of OLs or CPs

In Overtemperature Delta- for.Westinghouse (W)-designed

Temperature (OTAT) Set- nuclear power reactors.

point Caused by Improper

Gain Settings

86-14, Overspeed Trips of AFW, 08/26/91 All holders of OLs or CPs

Supp. 2 HPCI and RCIC Turbines for nuclear power reactors.

OL = Operating License

CP = Construction Permit