One of the best things to happen to the gasket and sealing industry is the flexible graphite. Graphite in its various forms is now being widely used for high temperature and moderate pressure sealing applications. This is now being offered in the forms such as sheet, ribbon, braided and ribbon pack.
It was at one time being used only for high temp applications, but of late, it is being used in low temperature applications too, as the prices have come down. Here a graphite sheet is now considered as cost effective high temperature / pressure material.
Graphite gasket materials are made from pure exfoliated exhibiting excellent sealing characteristics, withstanding a high range of temperatures, pressures and chemicals. The homogeneous material is free of respirable fibers, binders and additives.
Graphite flake sheets are able to withstand significantly more aggressive chemical environments (other than powerful oxidizing environments) and higher pressures than standard non-asbestos gasket materials. Metal inserted graphite is able to operate at even higher pressures.
It has a unique heat resistance to withstand temperature extremes from cryogenics through elevated levels. In reducing environments, pure graphite can handle up to 5000 F.
These sheets are typically available in thickness ranging from 1/32 "to" "thicknesses.
Standard grades are 95% – 98% pure graphite sheet% and a nuclear grade available at 99.5%. Graphite is extremely conformable giving it the ability to flow into flange surface imperfections. It's low permeability and chemical resistance make it an ideal choice as sealing material.
In oxidizing environments, in the past it was not recommended to use graphite, however with an inorganic passivation inhibitor to increase its oxidation and corrosion resistance, now its application range has widened further.
In order to use in applications where better rigidity of the gasket is required with a high operating pressure, reinforced graphite material has been introduced, which is another milestone in sealing industry.
A metal reinforced gasket is a rigid laminated gasket consisting of soft layers bonded to each face of a solid metal core by a high temperature / chemical resistant synthetic bonding agent.
While the solid metal core events gasket blowout, it provides high strength and rigidity: and the soft facings provide an exceptional seal. The soft facing material flows easily into the flange faces allowing a high integrity seal, even under low applied seating pressures.
Tanged steel reinforced graphite is a laminate sheet material of graphite foil layers mechanically bonded to a 0.1 mm (0.004 ") thick 316 stainless steel touched core. composites graphite foil chemically bonded to each face of a 0.05mm (0.002 ") 316 stainless steel substrate.
Please note that although flexible graphite material can withstand temperatures up to 1000 deg f, with larger sizes of the gaskets required, they may not be stable and may break during handling & installation.
Here, it is better to use stainless steel foil reinforced graphite gaskets, which will provide the sealing and temperature characteristics of graphite but at the same will provide stability to the gaskets, even with larger sizes.