A common mistake when selecting gasket material is to consider only the upper temperature limit. Excessive temperatures can lead to gasket failure, but so too can low temperatures. The Challenger Space Shuttle disaster is perhaps the best known example of this. Low temperature elastomers are worth looking at.
Gradual Transition
Metals are either solid or liquid with no fuzzy middle ground. Elastomeric materials like neoprene and SBR don’t have this clear melting/freezing point. They just become harder or softer. The dividing line is called the Glass Transition Temperature (Tg), but the difference in material behavior either side can be quite subtle. This makes it difficult for manufacturers of gasket materials to specify strict minimum temperatures. Instead, you’re more likely to see a range.
Elastomers and Low Temperatures
Low temperatures are a problem for elastomeric gasket materials, for two reasons:
- The lower the temperature the more the elastomer resists deformation under load. That’s bad because the material needs to squash into the faces being sealed.
- Low temperatures change compression set performance. A cold gasket material can take on a compression set and then leak as temperatures rise. (This is essentially what happened with the Challenger.)
Defining “Low”
In gasket terms, low temperatures are those which might be reached during winter in the upper Midwest. That means -20° to -40°F, which is far above the kind of cryogenic temperatures seen when processing and storing liquefied gases.
Gasket Material Selection
For very low temperatures, those down to -300°F, PTFE/Teflon gaskets are usually the material of choice. However, Teflon does tend to creep, making it unsuitable for some applications.
Silicone gaskets stay flexible at temperatures down to -80°F with some grades reaching -100°F. Nitrile rubber gaskets will typically work down to -80°F, although it’s important to check the material specs for details. Other elastomers harden before getting that cold, so always check material specifications.
Consider Both Temperature Extremes
Low temperatures can be as much of a problem for gasket materials as high temperatures. The loss of the Challenger serves as a reminder that gaskets may be exposed to temperatures below design limits.
Contact Hennig Gasket & Seals for your low temperature elastomer needs.
