When changing a gasket most technicians choose a new one made from the same material. If a paper, fiber or cork gasket came out of the joint, then the replacement is usually the same.
That’s not necessarily bad, assuming the gasket hadn’t failed prematurely, but it could also be a missed opportunity. Other gasket materials might hold up better in the application. That would allow more time between inspection and replacement, reducing downtime frequency and saving on maintenance hours.
Gasket materials are specified by multiple criteria, and the importance of each depends on what the application needs. One way of looking at these properties is to divide them into mechanical – their gap-filling ability – and material – how well they handle the media.
Mechanical properties
Whether looking for boiler seals or food grade gaskets, the primary considerations are thickness and hardness. Thickness is easy to understand, (always choose the thinnest that will do the job,) but hardness is less obvious. Gasket material hardness is reported in terms of Durometer, usually on the Shore A scale. (See “Measuring Gasket Material Hardness.”) When comparing two materials of the same thickness, the softer one is usually the better choice.
Other properties to look at are compressibility and creep relaxation. Compressibility measurement is defined by the ASTM F36 standard and describes the load needed to provide a given level of deformation. In general, higher compressibility implies lower loads are needed to secure a joint. Creep relaxation, addressed in ASTM F38, indicates how the gasket thins over time, which reduces bolt loading.
Material properties
Gasket material must be appropriate for the media. For example, nitrile gaskets are preferred for applications involving petroleum, mineral or vegetable oils but don’t perform well with ozones, ketones, esters and aldehydes.
The ability to handle expected temperatures is also important. This is especially critical where the environment causes severe temperature gradients through the joint. (Imagine piping liquid nitrogen in the desert southwest.) Nitrile gaskets may be appropriate for the media but an alternative, like silicone, might handle the temperatures better, (although has poor hydrocarbon resistance.)