ML18094B446

Part 21 Rept Re shaft-to-pinion Key Failures in Limitorque Actuators.Initially Reported on 900424.Caused by Reduction of cross-sectional Area & Ultimate Propagation of Cracks. Util Intends to Replace Keys in Actuators W/Keys of Steel

ML18094B446
Person / Time
Site:	Salem
Issue date:	04/27/1990
From:	Miltenberger S Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-90 NLR-N90093, NUDOCS 9005070251
Download: ML18094B446 (5)

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Public Service Electric and Gas Company Thomas M. Crimmins, Jr. Public Service Electric and Gas Company P.O. Box 236, Hancocks Bridge, NJ 08038 609-339-4700 Vice President - Nuclear Engineering April 27, 1990 NLR-N90093 United States Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 Gentlemen:

10CFR21 NOTIFICATION SHAFT-TO-PINION KEY FAILURES IN LIMITORQUE ACTUATORS SALEM GENERATING STATION DOCKET NO. 50-272 & 50-311 Pursuant to the notification requirements of 10 CFR Part 21, Public Service Electric and Gas Company (PSE&G) hereby provides a report of a materials misapplication in valve actuators supplied by Limitorque Corp. for six fast-closure butterfly valves used to isolate turbine building loads from the Service Water system under accident conditions.

The attached report more fully describes the particulars of this misapplication which was initially reported on April 24, 1990, by Mr. B. Preston of my staff, in a conference call with Messrs. W. Butler (NRR), P. Swetland (Region I) and R. Bailey (Limitorque).

Please contact us if you have any questions with regard to this transmittal.

Sincerely, Attachment

Document Control Desk 2 April 27, 1990 NLR-N90093 c Mr. J. c. Stone Licensing Project Manager Mr. T. P. Johnson Senior Resident Inspector Mr. T. Martin, Administrator Region I Mr. Kent Tosch, Chief New Jersey Department of Environmental Protection Division of Environmental Quality Bureau of Nuclear Engineering CN 415 Trenton, NJ 08625

. NLR-N90093 1 ATTACHMENT On April 24, 1990, PSE&G reported a materials misapplication concerning the pinion gear-to-shaft assemblies supplied by Limitorque Corporation under their Shop Order No. 11929904.

As described below, pinion-to-shaft keys have sheared under normal cycling operations and show evidence of deformation after 15 valve cycles.

Our investigation has determined that the problem at the Salem station is limited to six, 30 inch, fast-closure, quarter-turn, butterfly isolation valves installed in the Service Water system (three in each unit) . These valves isolate the turbine building thermal loads from the Service Water system during accident conditions.

CHRONOLOGY OF EVENTS On December 27, 1989, turbine isolation valve 21SW20 failed to operate. A work order was written and the pinion-to-shaft key was found to be sheared and badly damaged. A new key was taken from stock and installed. The valve was tested and returned to service. The remains of the damaged key were sent to the PSE&G Maplewood Research and Testing Laboratory for analysis. However, the results of the analysis were insufficient to determine the failure mechanism.

On March 20, 1990, during service water testing, turbine isolation valve 13SW20 failed mid-stroke. The valve was closed by hand to complete the testing evolution and a work order was written to address the problem. Disassembly of the actuator revealed that the pinion-to-shaft key had sheared. This key was replaced from stock and the Salem Technical Department initiated an investigation to determine the failure mechanism. PSE&G apprised Limitorque of the problem and sent them this second key for their analysis.

Again, the test results were inconclusive regarding cause.

A work order was then generated to inspect all the shaft keys on actuators supplied by Limitorque on that purchase order.

At the same time, the 38 keys in stock were sent to the Maplewood Lab for hardness testing. For this application, Limitorque had specified 1018 material with a hardness range of 160 - 280 (Brinell). One key tested at 190, the remaining 37 keys tested out between 160 and 180.

The results of the actuator inspection indicated no problems with the keys in 8 of the 14 actuators supplied under the purchase order in question. These 8 actuators are for valves that are not required to close within 10 seconds and do not experience the acceleration impact loading on their keyway assemblies that the fast-closure valves do.

. - NLR-N90093 2 ATTACHMENT All of the remaining six actuators are SMB-0, with 3600 rpm, 25 ftlb motors and are used in the same fast-closure application. All of these showed evidence of key damage, as follows:

21SW20 Inspected 12/27/89 - key was sheared Inspected 4/12/90 - new key had significant groove after 3 months of service 13SW20 Inspected 3/20/90 - key was sheared 1SW26 Inspected 4/12/90 - key was sheared and jammed, valve operated on demand 23SW20 Inspected 4/12/90 - key was sheared and jammed, valve operated on demand 11SW20 Inspected 4/12/90 - key was sheared and jammed, valve operated on demand Inspected 4/20/90 - key had two .005 grooves along sides after approx.12 cycles 2SW26 Inspected 4/12/90 - key was badly deformed On April 19, 1990, PSE&G made a four hour report on this matter in accordance with 10 CFR 50.72.

The key from 2SW26 was sent to the Maplewood Lab for evaluation. The key had two deep grooves running parallel to the axis and located approximately 180 degrees with

. respect to each other. The key was found to have a Brinell

- hardness of 164, which is near the bottom of the Limitorque specification of 160 to 280. Three of the four longitudinal corners of the key showed evidence of rounding; metallographic examination showed a deformed structure at these three locations. Metallographic examination also showed a deformed structure in the regions of the base of each groove. In addition, cracks were found which initiated at or near the base of the two grooves and extended inward toward the center of the key. Based on the detailed examination of this unfailed key and examination of failed keys, it is believed that failure occurs as a result of reduction of the cross-sectional area and the ultimate propagation of the cracks which form in the region of the base of the grooves.

,.

• NLR-N90093

• 3 ATTACHMENT On April 20, 1990, a Limitorque representative was onsite to witness the disassembly of the 11SW20 actuator. The cleanliness and visual condition of all components were checked and found to be acceptable (other than the grooving on the key). No alternate causative factors were identified by the representative.

CORRECTIVE ACTION PSE&G intends to replace the keys in the six valve actuators with keys made from a harder material, such as 4140 steel.

Since these valves are normally cycled about 30 times in a fuel cycle, we will install one of the new keys in one of the six actuators, cycle the valve a minimum of 60 times and inspect the key for wear. If no problems are noted, we will return the valves to service.

We will also inspect the keys in these six actuators during each outage until a permanent engineering resolution is determined.