Helium is used for cooling in electronics manufacturing. It’s used extensively for leak testing and it can be the inert gas in MIG and TIG welding. That means a lot of equipment needs gaskets to keep helium contained. Here’s some advice on what to use.
Only hydrogen has a lower atomic number than helium. That means, even compared to other atoms, helium atoms are small and light. Unlike hydrogen though, helium, (symbol: He) is very unreactive. It won’t burn or oxidize and doesn’t form compounds, all of which make it safe and easy to handle.
This “friendly” nature and small atomic size make helium the preferred gas in leak testing. If a pressure or vacuum chamber has even the smallest crack or pore helium will find a way through. In fact, helium is so good at finding holes in materials that it’s quite difficult to contain: at the atomic scale many materials have pores that helium can pass through.
Low Permeability Materials Needed
A material that lets helium pass is considered permeable. (The same material may be impermeable to larger atoms.) Permeability is measured in terms of the volume of gas that can pass through a given area in a set time.
Most polymers have a helium permeability coefficient. This indicates how well the material blocks the passage of helium. These values are useful when choosing appropriate gasket material.
Gasket Materials for Helium
Helium is so unreactive it can be used with any gasket made from an elastomeric polymer. The issue to watch for is permeation. (A gasket that lets the gas escape isn’t working very well!)
The polymer with the lowest helium permeation coefficient is nitrile rubber, (a.k.a. NBR or Buna N.) EPDM has only slightly higher permeation, closely followed by FKM/Viton. The material to avoid is silicone as helium can pass through it quite quickly.
When selecting a gasket for helium it’s also important to consider temperature and pressure along with compression set resistance. In most room temperature applications nitrile rubber/NBR/Buna N works well, but if in doubt, consult a material expert at Hennig Gasket.