Temperature bands
| Fluid | Boiling point (approx) |
|---|---|
| LNG | -162 degrees C |
| Liquid oxygen | -183 degrees C |
| Liquid nitrogen | -196 degrees C |
| Liquid hydrogen | -253 degrees C |
| Liquid helium | -269 degrees C |
Standard elastomers have glass transitions between -20 and -60 degrees C. Below that they are hard, brittle and non-sealing. Special low-temperature rubbers (some silicones, fluorosilicones, special FKM) stay flexible a little lower but not to cryogenic temperature.
Practical sealing solutions
- Spring-energised PTFE or other polymer seals. The spring maintains force when the jacket contracts.
- Metal seals (C-rings, E-rings, spring-energised metal) for the most demanding duty.
- Elastomer seals kept warm in a boot or extension (a warm-end seal on a long stem).
- Flexible graphite gaskets for flanges.
- Polymer composites (filled PTFE, PCTFE, polyimide) for seats.
Contraction
PTFE contracts about 2 percent from room temperature to cryogenic. Metals contract far less. The gland must accommodate differential contraction, or the seal pulls away from walls.
Oxygen service
- All parts must be oxygen-clean (no oil, grease or fibres).
- Use materials proven non-ignitable at the pressure and temperature, such as selected PTFE, PCTFE and FKM grades; check ASTM G63, G72, and G94 data.
- Avoid fillers that ignite (carbon, organics) unless qualified.
- Follow cleaning standards such as ASTM G93 or CGA G-4.1.
Testing
Cycle between ambient and cryogenic temperature at least 10 times and measure leak. Use real hardware, since seal and gland thermal gradients matter.
HPLT
At Pascalor, HPLT is the family of low-temperature, high-pressure duties. Specify the actual temperature, the pressure and the cycle count. Do not assume a compound described as "low temperature" works at -100 degrees C.
