Plastics and elastomers may be used for internal valve seats and seals. Plastics and nonmetallic materials that
maintain their integrity at elevated temperatures may be used for flange and valve packing and/or gaskets. AIGA 087/14 PAGE 5
Metallic gaskets are preferred for high pressure service. Graphite compounds also may be used with liquid
hydrogen.
When plastics and elastomers are used for gasketing, packing, or other sealing elements, the design should
incorporate features that minimize the release of hydrogen if the seal were to melt during a fire. These features
can include metal-to-metal or fire-resistant back-up seals. Alternatively, the design can restrict flow with close
clearances between metal parts or a tortuous flow path (such as stem threads).
Plastics such as PCTFE, PTFE, and polyamide (commonly known as Nylon®
) are commonly used. Elastomers
such as Buna-N (commonly known as Nitrile), chloroprene rubber (commonly known as Neoprene),
fluorocarbon rubber (commonly known as Viton®
), and other suitable compounds also may be used for
hydrogen gas service depending on the service temperature. At lower temperatures, these elastomers become
brittle and therefore shall not be used. Certain elastomers, especially low-durometer compounds, can fail
during rapid depressurization by explosive decompression. Only virgin stock material may be used. Recycled
or reprocessed material should not be used for hydrogen service.
Flanged joints on hydrogen vent piping shall have a metal-to-metal seal; a gasket of a material like graphite,
that is difficult to ignite; or shall be suitably protected from a fire. Soft elastomers and plastics are not
recommended.