A gasket is often the most practical and cost effective way to seal a bolted flange joint, however the problem for designers and maintenance engineers, with challenging media such as hydrogen at up to 100% concentration or mixed with H2S, CO2, or natural gas, is to select the correct type to ensure process integrity and safe operation.
Selection Guidelines
The specifications of gaskets for hydrogen piping may vary depending on various factors such as the pressure, temperature, and type of hydrogen being transported. However, some general guidelines can be considered as below.
Material
The gasket material should be compatible with hydrogen and not react with it. Generally, materials such as stainless steel, nickel alloys, and fluoropolymers are used for hydrogen piping gaskets.
Pressure rating
The gasket should have a pressure rating suitable for the piping system’s maximum operating pressure.
Temperature rating
The gasket should have a temperature rating suitable for the maximum operating temperature of the piping system.
Thickness
The thickness of the gasket should be appropriate for the flange type and size to ensure proper sealing.
Surface finish
The gasket surface finish should be smooth and free from any defects that could interfere with the sealing performance.
Compressibility
The gasket should have the right level of compressibility to ensure a tight seal and to compensate for any surface irregularities or flange misalignment.
Chemical resistance
The gasket should be resistant to the chemical environment of the hydrogen piping system.
“Due to the flammability of hydrogen, consideration should be given to the resistance to fire. Filled spiral-wound steel gaskets are preferred with raised flanges in general, but composition gaskets that are graphite based are also used at lower pressures. Soft metallic rings are preferred with joint ring flanges. “
Where welded connections are not practical, flanges are the next best choice. Leak-resistant flange types such as raised face, tongue, groove, or ring joint flanges shall be used. Gasket materials shall be appropriate for the design pressures and temperatures and be hydrogen-compatible and leak resistant.
In addition, due to the flammability of hydrogen, consideration should be given to the resistance to fire. Filled spiral-wound steel gaskets are preferred with raised flanges in general, but composition gaskets that are graphite based are also used at lower pressures. Soft metallic rings are preferred with joint ring flanges. Overall then, a Teflon or graphite-filled spiral wound gasket with a raised face flange or a copper ring with a joint ring flange are typical choices since they embody the desired features to a large extent. Since small leaks into the atmosphere present a significant safety risk, flange covers should be considered.
The designer must clearly understand the roles of different types of gaskets, their design, and the latest material technology in flange sealing, particularly in hydrogen applications where specific material grades, exceptional tightness, fire safety, electrical conductivity, or anti-static properties are critical.