Cracking of 1-inch UF sub 6 cylinder valve packing nuts: The effects of packing nut torque on stem seal leakage and packing nut stress due to thermal expansion of the PTFE stem seal rings
A series of tests has been conducted to correlate the torque applied to the packing nut of 1-in. uranium hexafluoride (UF{sub 6}) cylinder valves versus the stem seal leak rate and material strain. The tests were initiated as a result of discussions held at the 1989 spring meeting of the American National Standards Institute (ANSI) N14.1 committee. The packing nut has been observed to fail due to stress corrosion cracking. The specified level of torque applied to the packing nut to seal the stem packing has been suspected to be a contributor to the failures. The ANSI standard specifies torque of 120 to 150 ft-lb to compact the PTFE packing rings. One series of tests measured the effects of reduced levels of packing nut torque to the stem seal leak rate. The bubble leak rate of the stem was measured at ambient and 225{degree}F temperature with the body interior at 75 psig. Results from the laboratory tests indicate that the stem seal will perform acceptably through multiple thermal excursions at a torque level as low as 50 ft-lb. The second series of tests measured the effect of thermal expansion and increased hydrostatic force of the PTFE rings on the packing nut strain. The strain at certain exterior locations on a packing nut was measured at ambient and elevated temperatures for various assembly torques. The net increase in material strain is significant and is nearly equal at torque levels of 55, 85, and 115 ft-lb, being {minus}479, {minus}463, and {minus}469 {mu}in. respectively.
- Research Organization:
- Paducah Gaseous Diffusion Plant, KY (USA)
- Sponsoring Organization:
- DOE/NE
- DOE Contract Number:
- AC05-84OU21400
- OSTI ID:
- 5684105
- Report Number(s):
- KY/L-1549; ON: DE90001406
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
FASTENERS
STRESS CORROSION
SEALS
LEAKS
URANIUM HEXAFLUORIDE
CRACKS
POLYTETRAFLUOROETHYLENE
STRAINS
THERMAL EXPANSION
TORQUE
VALVES
ACTINIDE COMPOUNDS
CHEMICAL REACTIONS
CONTROL EQUIPMENT
CORROSION
EQUIPMENT
EXPANSION
FLOW REGULATORS
FLUORIDES
FLUORINATED ALIPHATIC HYDROCARBONS
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
HALOGENATED ALIPHATIC HYDROCARBONS
ORGANIC COMPOUNDS
ORGANIC FLUORINE COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC POLYMERS
POLYETHYLENES
POLYMERS
POLYOLEFINS
URANIUM COMPOUNDS
URANIUM FLUORIDES
360105* - Metals & Alloys- Corrosion & Erosion
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Handling
& Storage