ENS 48797
ENS Event | |
|---|---|
05:00 Dec 29, 2012 | |
| Title | Part 21 - Wedge Pin Failure in Anchor Darling Motor Operated Double Disc Gate Valves with Threaded Stem to Upper Wedge Connections |
| Event Description | The following is a summary of information received from Flowserve via facsimile:
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. 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. 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. Below 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 10 CFR 21 imposed. Flowserve plans to provide each of the customers identified [below] with a copy of this notification letter. The following facilities in the United States may be affected: ANO 1, Browns Ferry, Brunswick, Callaway, Catawba, Clinton, Columbia, Cook, Cooper, Crystal River, Dresden, Diablo Canyon, Duane Arnold, Fitzpatrick, Fort Calhoun, Grand Gulf, Hatch, Indian Point, Kewaunee, LaSalle, Limerick, Maine Yankee, Millstone, Monticello, Nine Mile, North Anna, Oconee, Oyster Creek, Peach Bottom, Perry, Pilgrim, Prairie Island, Quad Cities, River Bend, Robinson, San Onofre, St. Lucie, Surry, Three Mile Island 2, Waterford, VC Summer, Vermont Yankee, Wolf Creek. See Related Part 21 EN#48650.
The following is a summary of a report provided by Flowserve via email: This is to notify the US Nuclear Regulatory Commission that, in accordance with the provisions of 10 CFR Part 21, Flowserve has gained additional insight and information concerning the referenced previously reported issue based on a recent incident at the LaSalle County Station, Unit 2 involving a similar valve. Evaluation of a similar incident at LaSalle added an element not addressed in the previous evaluation regarding the limitation of a pressed-on stem collar to support the actuator thrust and maintain the stem-wedge preload. Valve evaluations and actions resulting from the previous notification are applicable and still apply. This notification includes additional information for maintaining the stem preload that was not addressed previously. The actuator thrust as well as the torque must be reviewed to insure the preload is maintained. A list of customers, utilities and nuclear plants which were supplied with Anchor/Darling DD Gate valves with motor actuators on contracts with Section 111 and/or 10CFR21 was provided. This list added a few sites not included on the list provided with the original notification. For questions or additional information please contact: Joseph Carter Manager, Quality Assurance Flowserve Corporation, FCD Raleigh, NC 919-831-3220 Notified R1DO(Dimitriadis), R2DO(Bonser), R3DO(Peterson), R4DO(Proulx), Part 21 group (via email). |
| Where | |
|---|---|
| Anchor Darling Raleigh, North Carolina (NRC Region 1) | |
| Organization: | Flowserve |
| Reporting | |
| 10 CFR 21.21(d)(3)(i), Failure to Comply or Defect | |
| Time - Person (Reporting Time:+1494.2 h62.258 days <br />8.894 weeks <br />2.047 months <br />) | |
| Opened: | James Tucker 11:12 Mar 1, 2013 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Jul 11, 2017 |
| 48797 - NRC Website
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Anchor Darling with 10 CFR 21.21(d)(3)(i), Failure to Comply or Defect | |
WEEKMONTHYEARENS 487972012-12-29T05:00:00029 December 2012 05:00:00
[Table view]10 CFR 21.21(d)(3)(i), Failure to Comply or Defect Part 21 - Wedge Pin Failure in Anchor Darling Motor Operated Double Disc Gate Valves with Threaded Stem to Upper Wedge Connections 2012-12-29T05:00:00 | |