ENS 53151
ENS Event | |
|---|---|
05:00 Nov 22, 2017 | |
| Title | Part 21 - Defect in Thermostatic Valve Assemblies |
| Event Description | The following information was excerpted from a facsimile received from Engine Systems, Inc.:
Two thermostatic valve assemblies were supplied by [Engine Systems, Inc.] ESI that were found to have retaining straps, subcomponents of the internal thermostatic element, detached from the correct position. For each valve assembly, one of the thermostatic elements (the centrally located element) contained this defect. The straps are used in conjunction with a spring to retain the element in a closed position. As the temperature of the sensed fluid increases, a temperature sensitive wax expands to open the element while acting against the spring. As the temperature of the fluid decreases, the wax contracts and the spring returns the element to its closed position. Absence or failure of the straps would prevent proper operation of the element. The thermostatic valve assembly is used on an emergency diesel generator [EDG] set to regulate the temperature of lubricating oil (other EDGs use this same type of valve for jacket water temperature regulation). If one of the elements within the assembly were to fail, as is the case with a missing strap, regulating capacity of the thermostatic valve could be affected. However, the failure mode in the case of missing straps is in the open position (element does not return closed) and the remaining eight elements would compensate by closing to regulate the fluid temperature. More importantly, detached retaining straps could migrate to other components in the lube oil system. Acting as foreign material, the straps could adversely affect the ability of these critical components to perform their safety-related function within the emergency diesel generator's lube oil piping. The foreign material aspect of this defect makes it a reportable issue. Information of such defect or failure to comply was obtained on November 22, 2017. This issue is an isolated incident affecting two thermostatic valves supplied to one nuclear plant [DC Cook]. The nuclear plant detected the issue during inspection and returned the assemblies to ESI. No further action is required on the part of DC Cook. ESI's investigation revealed that this issue was induced by a test technician who, in an effort to minimize the amount of test fluid remaining in the assembly after pressure testing, manually actuated the center thermostatic element (there are 9 total elements) to drain a small pocket of residual fluid. This effort to prevent the formation of oxidation had an unintended consequence and resulted in a more serious issue. Though this is an isolated incident as it pertains to items supplied from ESI, this same model thermostatic valve assembly is used extensively on EDGs in the nuclear industry. Those customers that perform valve maintenance, including thermostatic element replacement, should be aware of the possibility of the straps becoming detached if care is not taken. If you have any questions, you may call: Tom Horner Quality Assurance Manager Tel: (252) 977-2720 ESI Report ID: 10CFR21-0120, Rev. 0, dated 01/05/18 |
| Where | |
|---|---|
| Engine Systems, Inc Rocky Mount, North Carolina (NRC Region 1) | |
| Organization: | Engine Systems, Inc |
| Reporting | |
| 10 CFR 21.21(a)(2), Interim Report for Comply or Defect in Component | |
| Time - Person (Reporting Time:+1068.27 h44.511 days <br />6.359 weeks <br />1.463 months <br />) | |
| Opened: | Tom Horner 17:16 Jan 5, 2018 |
| NRC Officer: | David Aird |
| Last Updated: | Jan 5, 2018 |
| 53151 - NRC Website | |
Engine Systems, Inc with 10 CFR 21.21(a)(2), Interim Report for Comply or Defect in Component | |
WEEKMONTHYEARENS 538462018-12-06T05:00:0006 December 2018 05:00:00
[Table view]10 CFR 21.21(a)(2), Interim Report for Comply or Defect in Component En Revision Imported Date 3/22/2019 ENS 531512017-11-22T05:00:00022 November 2017 05:00:00 10 CFR 21.21(a)(2), Interim Report for Comply or Defect in Component Part 21 - Defect in Thermostatic Valve Assemblies 2018-12-06T05:00:00 | |