What types of gaskets are there?

Flange gaskets can be grouped into three primary groups.

Non-metallic / Soft gaskets
Used in low-pressure applications. They should not be used in high-pressure applications because of their propensity to blow out.

These gaskets come in two different designs. Full face gasket design is used with flat face flanges. Ring gasket design is used in raised face applications. A partial list of materials includes Compressed non-asbestos fiber, PTFE, Red rubber, EPDM, Buna-N, and Ceramic fiber.

Metallic / Hard gaskets
Rely on plastic deformation of the gasket material to form a seal. They have excellent sealing ability at high pressures and become more common in higher-pressure classes. A common list of designs includes; Corrugated Soft Iron, Oval ring, Octagonal ring, RX ring, and BX ring. All except the corrugated are used with RTJ flanges.

Semi-metallic / Composite gaskets
A combination of metal and non-metallic materials like graphite and PTFE. The combination increases the blowout resistance. Some composite gaskets are Spiral wound, Metal jacketed, Camprofile, Graphonic, or Telflonic.