If you need an alternative to PTFE gasket material, how about graphite? Produced as sheet material, flexible graphite gasket material withstands high temperatures while deforming easily enough to take up imperfections in flange surfaces.
Chemistry and Production
Graphite is a form of carbon. It’s used in pencils because it’s easy to slide the layers apart and spread them on paper. To produce a useful gasket material the graphite is first expanded and then passed through a machine called a sheeter.
Expanding entails exposing small pieces of graphite to sulfuric or nucleic acid. These force the atomic layers apart, making the graphite expand dramatically and forming what look like tiny worms. These “worms” are then fed into a sheeter that compacts them into a sheet of flexible graphite material.
For added strength, the graphite can be laminated onto either a thin stainless steel foil or a stainless tang.
Properties of Flexible Graphite Gasket Material
The practical upper-temperature limit is around 750 °F (399 °C) although some grades will go to 900 °F (482 °C). You may see claims that graphite can withstand temperatures as high as 5,400 °F (2,982 °C) but this is in an oxygen-free atmosphere, which few gaskets ever experience.
A limitation of sheet form expanded graphite is low tensile strength. Laminating onto 316 stainless raises this from around 700 psi to a much more useful 5,000psi. In terms of gasket applications, this means pure graphite sheet has very low resistance to pressure: foil and tang forms of graphite sheet are far more useful.
The downside of combining graphite with stainless is that this slightly reduces both compressibility and recovery behavior.
Graphite has excellent resistance to water, steam, hydrocarbons, and many acids and alkalies. However, sulfuric or nucleic acids will cause rapid decomposition. Note that graphite is not suitable for food, medical or pharmaceutical applications because there’s a possibility of releasing carbon particles into the fluid.
Flexible Graphite Gaskets Cut to Size
Hennig Gasket & Seals carries flexible graphite gasket material in a range of thicknesses. Gaskets can be cut to sizes up to 48” in diameter. Contact us for more information.