ML13064A012
| ML13064A012 | |
| Person / Time | |
|---|---|
| Site: | Millstone, Hatch, Monticello, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Oconee, Nine Mile Point, Perry, Indian Point, Kewaunee, Catawba, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Grand Gulf, Pilgrim, Arkansas Nuclear, Three Mile Island, Summer, Prairie Island, Columbia, Brunswick, Surry, Limerick, North Anna, River Bend, Vermont Yankee, Crystal River, Diablo Canyon, Callaway, Waterford, Duane Arnold, Robinson, Clinton, San Onofre, Cook, Maine Yankee, Quad Cities, Fort Calhoun, FitzPatrick, LaSalle  |
| Issue date: | 02/25/2013 |
| From: | Tucker J Flowserve Corp |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML13064A012 (7) | |
Text
Flow Control Division Anchor/Darling Valves FLOWSERV BWI/P Valves Edward Valves Valtek Control Products Worcester Valves February 25, 2013 US Nuclear Regulatory Commission Document Control Desk 11545 Rockville Pike Rockville MD 20852-2746
Subject:
Wedge Pin Failure of an Anchor/Darling Double- Disc Gate Valve at Browns Ferry Nuclear Plant Unit 1
Reference:
Tennessee Valley Authority's 10CFR Part 21 Notification Letter Dated January 4, 2013 and Flowserve Letter to the NRC dated January 25, 2013. : Recommended Stem Pre-Torque for Stem Upper Wedge : List of Potentially Affected Customers and Plants Gentlemen:
This is to notify the US Nuclear Regulatory Commission that, in accordance with the provisions of 10CFR Part 21, we have identified a potential issue and are submitting our evaluation of the event.
Flowserve has been working with the Tennessee Valley Authority's (TVA) Browns Ferry Nuclear Plant to investigate the failure of a Size 10, Class 900 Anchor/Darling motor-operated double-disc gate valve. The failure was due to the shearing of the wedge pin which serves a joint locking function at the threaded interface between the valve stem and upper wedge. The pin is designed to ensure that the joint does not loosen due to vibration and other secondary loads. On some valve designs, the pin also is used to attach the disc retainers to the upper wedge. The pin shearing allowed rotation of the stem during the closing stroke when the valve was seating and ultimately resulted in loss of the stem to upper wedge joint integrity.
Flowserve has completed an evaluation of the failure and concluded the root cause of the wedge pin failure was excessive load on the pin. The stem operating torque exceeded the torque to tighten the stem into the upper wedge before installation of the wedge pin. The additional stem torque produced a load on the wedge pin creating a stress which exceeded the pin shear strength causing the failure. The recommended assembly stem torque did not envelope the operating torque for the TVA application providing the potential for an over load situation and ultimate failure. The operating torque for the TVA valve was unusually high due to the fast closing time of the actuator and very conservative closing thrust margin.
Flowserve US Inc Raleigh Operations Toll Free: 1-800-225-6989 Flow Control Division PO Box 1961 Phone: 1-919-832-0525 1900 South Saunders Street Facsimile: 1-919-831-3369 Raleigh, NC 27603 www.flowserve.com
This situation can potentially occur on any Anchor/Darling type double-disc gate valve with a threaded stem to upper wedge connection, typically size 2.5" and larger, operated by an actuator that applies torque on the stem to produce the required valve operating thrust. An operating stem torque greater than the assembly stem torque can provide the opportunity for excessive pin load and potentially failure.
The stems on most double-disc (DD) gate valves larger than size 2" are attached to the upper wedge using UN threads. A pin is installed through the hub of the upper wedge and stem threaded section to prevent the stem from loosening and eventually unscrewing from the wedge. In addition, the disc retainers on some DD gate valves are attached using the wedge pin. See Figure 1. The output torque of the actuator is transmitted to the stem/wedge joint through the stem and is resisted by the disc wedge pack, therefore the stem to wedge connection is loaded by the stem torque and thrust.
The wedge pin is not designed to withstand the full actuator output torque. The actuator torque direction tends to tighten the stem into the wedge during closing and tends to loosen the stem during opening.
Figure 1 Typical Double-Disc Gate Valve Trim VERTICAL STEM BACKSEAT (STEM CENTERLINE)
STEM STEM THREADS BODY HORIZONTAL I(PORT CENTERLINE)
Flowserve US Inc Raleigh Operations Toll Free: 1-800-225-6989 Flow Control Division PO Box 1961 Phone: 1-919-832-0525 1900 South Saunders Street Facsimile: 1-919-831-3369 Raleigh, NC 27603 www.flowserve.com Page 2 of 7
Anchor Darling double-disc gate valves have been supplied to the commercial nuclear industry for critical service since the early 1970's. In April 1996, a specific stem preload torque value was established based on valve size and pressure class. This recommended standard stem preload torque is based on a calculated, required stem thrust to close the valve which is considered great enough to envelope most applications. Attachment 1 details the recommended torque by valve size and pressure class.
Failure of the wedge pin can cause loosening of the stem in the upper wedge and eventually separation of the stem leaving the valve inoperable. For certain designs pin failure could allow the retainers and miscellaneous attachment parts to fall out of position and become loose parts in the valve and piping system.
We have reviewed our records, and the only similar wedge pin failure that we can identify, in addition to the Browns Ferry problems, is a sheared wedge pin at LaSalle Nuclear Station in 1993. Our investigation of the LaSalle failure concluded that the wedge pin failed due to excessive torque in the opening direction due to bonnet over pressurization.
Flowserve recommends that all critical Anchor/Darling Double-Disc Gate valves with threaded stem to upper wedge connections and actuators that produce a torque on the stem be evaluated for potential wedge pin failure. Valves with electric motor actuators which produce high output torques are the most susceptible to failure. Valves which were assembled with stem torques that exceed the operating torque are not candidates for failure.
There is no test or inspection method to determine if the stems were completely torqued into the upper wedge prior to pin installation. Abnormal rotation of the stem immediately after valve seating or unseating, short valve stroke, or poor, unusual operation are signs of possible issues and should be investigated. Valve stems which have any gap between the stem backseat and top of the upper wedge need to be re-torqued. Valves with operating torques greater than the stem installation torque should be corrected by increasing the stem installation torque to at least the maximum expected operating stem torque. As provided in the Anchor/Darling 12/05 instruction manual, the existing stem can be reused by torqueing and drilling for a new pin if it is greater than 1.50" diameter and not reused previously. Stems of 1.50" and less diameter or stems which cannot be re-drilled for a new pin should be replaced. is a list, based on our records, of customers, utilities and nuclear plants which were supplied with Anchor/Darling Double-Disc Gate valves with motor actuators on contracts with ASME Section III and/or 10CFR21 imposed.
Flowserve plans to provide each of the customers identified in Attachment 2 with a copy of this notification letter.
Flowserve U S Inc Raleigh Operations Toll Free: 1-800-225-6989 Flow Control Division PO Box 1961 Phone: 1-919-832-0525 1900 South Saunders Street Facsimile: 1-919-831-3369 Raleigh, NC 27603 www.flowserve.com Page 3 of 7
Please do not hesitate to contact me if you have questions or require additional information.
Respectfully submitted,
)ames P. Tucker Manager, Engineering Flowserve Corporation Flow Control Division 1900 S. Saunders St.
Raleigh, NC 27603 Flowserve U S Inc Raleigh Operations Toll Free: 1-800-225-6989 Flow Control Division PO Box 1961 Phone: 1-919-832-0525 1900 South Saunders Street Facsimile: 1-919-831-3369 Raleigh, NC 27603 www.flowserve.com Page 4 of 7
ATTACHMENT 1 RECOMMENDED STEM PRE-TORQUE (FT-LBS) FOR STEM/UPPER WEDGE JOINT ANCHOR-/ DARLING DOUBLE-DISC GATE VALVES VALVE PRESSURE CLASS SIZE 150 300 600 900 1500 2500 2.5 11 13 21 38 60 114 3 17 16 26 48 89 171 4 25 28 57 82 154 292 6 42 57 139 228 414 844 8 46 104 275 444 805 1848 10 74 172 483 776 1497 3436 12 110 262 720 1240 2467 5436 14 156 380 1022 1726 3434 7409 16 215 528 1398 2346 4844 9699 18 289 770 1955 3250 6888 12394 20 377 1006 2496 2960 9003 15750 22 448 1355 N/A N/A N/A N/A 24 604 1697 3724 6999 14154 25132 Flowserve US Inc Raleigh Operations Toll Free: 1-800-225-6989 Flow Control Division PO Box 1961 Phone: 1-919-832-0525 1900 South Saunders Street Facsimile: 1-919-831-3369 Raleigh, NC 27603 www.flowserve.com Page 5 of 7
ATTACHMENT 2 ANCHOR/DARLING DOUBLE-DISC GATE VALVES WITH WEDGE PINS AND MOTOR ACTUATORS AE / UTILITY NUCLEAR PLANT B&W THREE MILE ISLAND 2 BECHTEL ANO 1, CALLAWAY, WOLF CREEK, MILSTONE CFE LAGUNA VERDE COM ED DRESDEN, LASALLE, QUAD CITIES CPL BRUNSWICK, ROBINSON DOMINION SURRY DUKE CATAWBA, OCONEE EBASCO MILLSTONE ENTERGY GRAND GULF, NINE MILE, WATERFORD EXELON PEACH BOTTOM, FPL CRYSTAL RIVER, ST. LUCIE GE BROWNS FERRY, BRUNSWICK, CHINSHAN, CLINTON, COLUMBIA, CONFENTES GE COOPER, DUANE ARNOLD, FITZPATRICK, FORT CALHOUN, FUKISHIMA GE GRAND GULF, HATCH, KUOSHENG, LAGUNA VERDE, LASALLE, LIMERICK GE NINE MILE, PEACH BOTTOM, PERRY, PILGRIM, RIVER BEND, SHIMANE GPC HATCH GPU OYSTER CREEK GULF STATES RIVER BEND ILL POWER CLINTON INDIANA MICH POWER COOK MAINE YANKEE MAINE YANKEE NEU MILLSTONE NIAGARA MOHAWK NINE MILE NORTHEAST NUC MILLSTONE NPPD COOPER NSP MONTICELLO, PRARIE ISLAND NYPA FITZPATRICK ONT HYDRO BRUCE PG&E DIABLO CANYON PHILA ELECTRIC PEACH BOTTOM PPL SSES PROGRESS ENERGY ROBINSON SCE SAN ONOFRE SCE&G VC SUMMER SNC LAVALIN BRUCE Flowserve US Inc Raleigh Operations Toll Free: 1-800-225-6989 Flow Control Division PO Box 1961 Phone: 1-919-832-0525 1900 South Saunders Street Facsimile: 1-919-831-3369 Raleigh, NC 27603 www.flowserve.com Page 6 of 7
TPC CHINSHAN, KUOSHENG, LUNGMEN TVA BROWNS FERRY VEPCO NORTH ANNA, SURRY VERMONT YANKEE VERMONT YANKEE WESTINGHOUSE COOK, DIABLO CANYON, INDIAN POINT, KANSAI ELECTRIC, KEWAUNEE WESTINGHOUSE KORI 1, NORTH ANNA, POINT BEACH, PRAIRIE ISLAND, RINGALS, ROBINSON Flowserve US Inc Raleigh Operations Toll Free: 1-800-225-6989 Flow Control Division PO Box 1961 Phone: 1-919-832-0525 1900 South Saunders Street Facsimile: 1-919-831-3369 Raleigh, NC 27603 www.flowserve.com Page 7 of 7