Double-jacketed gaskets are probably the most commonly used style of gaskets in heat exchanger applications. They are available in virtually any material that is commercially available in 26-gauge sheet. They are also extensively used in standard flanges where the service is not critical. Since most double-jacketed gaskets are custom made, there is virtually no limit to size, shape or configuration in which these gaskets can be made.
In some cases nubbins are provided on heat exchanger designs to provide an intermediate seal. This nubbin is normally 1/64" high by 1/8" wide. Experience has indicated, however, that there is little advantage to this particular design. The primary seal is still dependent on the inner lap of the gasket doing the brute work and the secondary seal, when applicable, would be provided by the outer lap.

Double-jacketed gaskets are probably the most commonly used style of gaskets in heat exchanger applications. They are available in virtually any material that is commercially available in 26-gauge sheet. They are also extensively used in standard flanges where the service is not critical. Since most double-jacketed gaskets are custom made, there is virtually no limit to size, shape or configuration in which these gaskets can be made.
In some cases nubbins are provided on heat exchanger designs to provide an intermediate seal. This nubbin is normally 1/64" high by 1/8" wide. Experience has indicated, however, that there is little advantage to this particular design. The primary seal is still dependent on the inner lap of the gasket doing the brute work and the secondary seal, when applicable, would be provided by the outer lap.