Information Notice 1994-49, Failure of Torque Switch Roll Pins

Failure of Torque Switch Roll Pins
	ML031060612
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:	07/06/1994
From:	Grimes B; Office of Nuclear Reactor Regulation
To:	;
References
	IN-94-049, NUDOCS 9406280321
	Download: ML031060612 (27)
	v • d • e

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UNITED STATES i

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON D.C. 20555 July 6, 1994 NRC INFORMATION NOTICE 94-49: FAILURE OF TORQUE SWITCH ROLL PINS

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 potential inservice failure of the torque

switch roll pin in Limitorque Corporation (Limitorque) actuators. It is

expected that recipients will review the information for applicability to

their facilities and consider actions, as appropriate, to avoid similar

failures. HowLver, suggestions contained in this information notice are not

NRC requirements; therefore, no specific action or written response is

required.

Description of Circumstances

Pilgrim Nuclear Power Station, Unit 1.

On March 9, 1994, after a surveillance test of a motor-operated valve (MOV) in

the high-pressure coolant injection (HPCI) system, the MOV could not be opened

after being closed. The failed valve is a normally open test and maintenance

valve on the pump discharge line. When closed, the valve maintains the

pressure isolation boundary during inservice stroke time testing of the

normally closed HPCI system injection valve; it receives an open signal upon

initiation of the HPCI automatic start logic. The MOV breaker tripped open on

overload and prevented the MOV from being opened remotely as designed. The

valve is operated by a Limitorque SMB-O actuator (Licensee Event Report

(LER) 50-293/94-002).

Evaluation of this failure revealed that the direct cause of the inability of

the MOV to open was the failure of the MOV torque switch drive pinion gear

roll pin. With the roll pin broken-, the torque switch did not deenergize the

motor upon completing the clooestroke and the MOV electrical breaker tripped

open. The licensee, Boston Edison Company, declared the HPCI system

inoperable and determined that an increase in the impact load on the roll pin

apparently resulted from high pullout thrust and increased forces due to

hardened grease i: the tq'rque switch spring pack. The licensee learrnd about

a hammering of the torque,switch on valve unseating observed at another

nuclear power plant (described below for Washington Nuclear Project, Unit 2)

and considered that this dynamic effect might also have contributed to the

roll pin failure at the Pilgrim plant. The licensee concluded that the roll

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IN 94-49 July 6, 1994 pin design, a small diameter pin (2.4 mm [3/32 in.]) made of relatively

brittle high carbon steel (American Iron and Steel Institute (AISI) 1070), was

the root cause of the failure.

The licensee opened the failed MOV to its safety position, returned the HPCI

system to an operable status, and established corrective action to replace the

failed torque switch model with one that has a larger diameter roll pin of

improved material. The licensee evaluated the potential for this problem to

affect those MOVs that must close during an accident scenario and subsequently

reopen. The licensee determined that such MOVs are operable with the existing

roll pin design. As MOVs are disassembled for diagnostic testing, the

licensee plans to install spring packs with internal relief devices to prevent

grease hardening in the spring pack.

Hope Creek Nuclear Station, Unit 1.

On August 14, 1993, during inservice testing of valves, a HPCI pump discharge

valve failed to fully open during an open stroke test. The valve, a 14-inch, horizontally mounted, flexible wedge gate valve, provides coolant from the

HPCI system to the core spray system during actuation of the emergency core

cooling system. The motor overload contacts for this same valve tripped

during the subsequent close stroke. The valve is operated by a Limitorque

SB-3 actuator (LER 50-354/93-005).

Evaluation of this failure revealed that the torque switch roll pin was

broken, probably because of shearing forces. The failure of the roll pin

allowed premature torque switch actuation on the open stroke and failure of

torque switch actuation on the close stroke. The licensee, Public Service

Electric and Gas Company, replaced the torque switch and is administratively

controlling the number of valve strokes for this valve as part of an ongoing

root-cause evaluation. The licensee plans to complete the root-cause

evaluation and perform further diagnostic testing during the next planned

outage in the spring of 1994.

Four previous torque switch roll pin failures have occurred at the Hope Creek

Station. Three of these failures (March 1988, November 1989, and September

1991) involved the same HPCI pump discharge valve actuator that was involved

in the failure that occurred in August 1993. The fourth failure, in November

1990, involved an SMB-1 actuator installed vertically in the HPCI steam supply

line. Each of the valves is stroke-tested quarterly in accordance with the

American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel

Code,Section XI, "Inservice Testing."

Washington Nuclear Project, Unit 2.

In August 1993, the licensee, Washington Public Power Supply System, notified

Limitorque about a r-oblem with torque switch roll pins in MOV actuators with

model numbers SB/SMB 0 through 5. The valves were apparently sticking in

their seats when closed and causing increased stress on the torque switch roll

pin during valve unseating (see Pilgrim LER 50-293/94-002).

IN 94-49 July 6, 1994 Palo Verde Nuclear Station, Units 1, 2, 3.

On May 26, 1992, the licensee, Arizona Public Service Company, requested

technical assistance in a letter to Limitorque to address failures of torque

switch roll pins. The licensee had experienced at least 14 failures of pins

(roll and groove pins) in torque switches on 10 different MOV actuators. Two

failures occurred in actuators with model number SMB-OO, two for SB-0, eight

for SMB-1, and two for SB-3. (NRC Inspection Reports 50-528/94-11,

50-529/94-11, 50-530/94-11).

Using strain gages, the licensee found the dynamic torque during operation to

be excessive during rapid acceleration (snapback) of the spring pack

immediately following unseating of the valve. The licensee found that for

actuators with model SB that have a lost motion drive sleeve (hammerblow

feature), the compensator spring increased the snapback acceleration.

The licensee observed another effect of impact loading of the torque switch.

During unseating of the valve, the torque switch contact bar flipped onto its

side, interrupting electrical continuity and motor operation as though the

torque switch had actuated. The licensee replaced the contact bar compression

springs with stiffer springs and attributed the root cause to the recoil force

that impacts the contact bar when the valve is unseating.

Discussion

On March 23, 1994, Limitorque submitted a report to the NRC in response to the

recent failures of torque switch roll pins, in accordance with Part 21 of

Title 10 of the Code of Federal ReQulations (Part 21 report). This report

discusses potential failures of the torque switch roll pin in Limitorque MOV

actuators with model numbers SMB/SB/SBD-O through -4, -4T, -5, -5T, and -5XT.

Limitorque stated that (1) it did not have the required expertise relative to

valve and system design to perform a root cause analysis of these potential

failures, (2) an affected isolation valve that must move from its open

position to its closed position may not reopen reliably, (3) an affected

injection valve would open and close, provided that no abnormal conditions

were present during the previous valve closure, such as thermal overload trip

or excessive motor current, (4) the licensee corrective action is to acquire

and analyze site data relative to this issue, (5) Limitorque modified the roll

pin design by replacing the 2.4 mm [3/32-in.] diameter pins with 3.2 mm

[1/8-in.] diameter shear-proof pins and (6) Limitorque will replace the

303 stainless steel shaft material for new torque switches with 416 stainless

steel material.

On December 11, 1990, Limitorque submitted a Part 21 report of the potential

failure of the torque switch roll pin in SMB-O0 actuators. This report

limited the scope of concern to MOV actuators with model numbers SMB-, SB-,

and SBD-OO that have heavy spring packs that are declutched under ma; ,irur'

rated load.

The recent torque switch roll pin failures occurred during motor-driven

operation of the MOVs. In contrast, the Limitorque Part 21 report dated

)

IN 94-49 July 6, 1994 December 11, 1990, discusses failures during declutching of the actuator under

loaded conditions to allow manual operation.

Related Generic Communications.

Potential overthrusting of motor-operated valves is discussed in NRC

Information Notice 92-83, "Thrust Limits for Limitorque Actuators and

Potential Overstressing of Motor-Operated Valves," issued March 27, 1992.

Information Notice 92-83 discusses several industry qualification testing

programs that are being used by licensees to increase motor-operated valve

thrust allowable limits. These higher thrust limits may cause various

actuator subcomponents, including torque switch roll pins, to be subjected to

higher stress levels and thus to incur higher failure rates.

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, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: James S. Stewart, RI

(215) 337-5240

Thomas G. Scarbrough, NRR

(301) 504-2794 Christopher Myers, RIV

(510) 975-0260

Attachment:

List of Recently Issued NRC Information Notices

I )7

0

Attachment

IN 94-49 July 6, 1994 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

94-48 Snubber Lubricant 06/30/94 All holders of OLs or CPs

Degradation in High- for nuclear power reactors.

Temperature Environments

94-13, Unanticipated and Unin- 06/28/94 All holders of OLs or CPs

Supp. 1 tended Movement of Fuel for nuclear power reactors.

Assemblies and other

Components due to Improper

Operation of Refueling

Equipment

94-47 Accuracy of Information 06/21/94 All U.S. Nuclear Regulatory

Provided to NRC during Commission Material

the Licensing Process Licensees.

94-46 NonConservative Reactor 06/20/94 All holders of OLs or CPs

Coolant System Leakage for nuclear power reactors.

Calculation

94-45 Potential Common-Mode 06/17/94 All holders of OLs or CPs

Failure Mechanism for for nuclear power reactors.

Large Vertical Pumps

94-44 Main Steam Isolation 06/16/94 All holders of OLs or CPs

Valve Failure to Close for nuclear power reactors.

on Demand because of

Inadequate Maintenance

and Testing

94-43 Determination of Primary- 06/10/94 All holders of OLs or CPs

to-Secondary Steam for pressurized water

Generator Leak Rate reactors.

94-42 Cracking in the Lower 06/07/94 All holders of OLs or CPs

Region of the Core for boiling-water reactors

Shroud in Boiling-Water (BWRs).

Reactors

OL = Operating License

CP = Construction Permit

VV IN 94-49 July 6, 1994 December 11, 1990, discusses failures during declutching of the actuator under

loaded conditions to allow manual operation.

Related Generic Communications.

Potential overthrusting of motor-operated valves is discussed in NRC

Information Notice 92-83, "Thrust Limits for Limitorque Actuators and

Potential Overstressing of Motor-Operated Valves," issued March 27, 1992.

Information Notice 92-83 discusses several industry qualification testing

programs that are being used by licensees to increase motor-operated valve

thrust allowable limits. These higher thrust limits may cause various

actuator subcomponents, including torque switch roll pins, to be subjected to

higher stress levels and thus to incur higher failure rates.

Onginal signed by

Bdan L GWme

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: James S. Stewart, RI

(215) 337-5240

Thomas G. Scarbrough, NRR

(301) 504-2794 Christopher Myers, RIV

(510) 975-0260

Attachment:

List of Recently Issued NRC Information Notices

SEE PREVIOUS CONCURRENCE

OFFICE *OGCB *TECH ED. *REGION I *D:DRS/REGION I *EMEB/DE

NAME CVHodge RSanders JSStewart MWHodges TGScarbrough

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12/15/93 02/17/94 05/31/94 03/03/94 06/3f94 UULUMtN I NAML: 94-49.IN

IN 94-XX

March xx, 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, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical Contacts: James S. Stewart, Region I

(215) 337-5240

Thomas G. Scarbrough, NRR

(301) 504-2794 Attachments:

List of Recently Issued Information Notices

SEE PREVIOUS CONCURRENCE

OFFICE *OGCB *TECH ED. *REGION I *D:DRS/REGION I

NAME CYHodge RSanders JSStewart MWHodges

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12/08/93 12/15/93 02/17/94 03/03/94 03/ /94 DOCUMENT NAME: TORQSWIT.INF-3

\\> IN 94-XX

May xx, 1994 Information Notice 92-83 discusses several industry qualification testing

programs that are being used by licensees to increase motor-operated valve

thrust allowable limits. These higher thrust limits may cause various

actuator subcomponents, including torque switch roll pins, to be subjected to

higher stress levels and thus to incur higher failure rates.

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, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical Contacts: James S. Stewart, Region I

(215) 337-5240

Thomas G. Scarbrough, NRR

(301) 504-2794 Christopher Myers, Region IV

(510) 975-0260

Attachment:

List of Recently Issued Information Notices

_FF PRFV.OUS CONCURRENCE

OFFICE J *OGCB *TECH ED. *REGION I *D:DRS/REGION I

NAME CVHodge RSanders JSStewart MWHodges

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