A gasket, abbreviated GSKT, is a material that is used to seal the face of flanges, valves and equipment. Gaskets can be made from materials that are soft or hard, but will compress to make a tight seal. When compressed between two flange faces it will deform to match the surface grooves and irregularities. A gasket must be installed properly to prevent leakage. The surface of the flange must be clear of all foreign bodies such as dust, dirt or grease that could prevent a proper seal. To ensure a seal through out the life of the gasket, sufficient pressure or stress should be maintained to prevent leakage. It is very important to select the right gasket material to be used.
Gasket materials can be divided into three basic categories:
- Non-metallic gasket - or "soft gaskets" are made from materials that are easily compressed under a low bolt load. They can be used with both flat and raised face flanges in low pressure applications. Materials used are different types of rubber, PTEF, ceramic fiber, glass fiber and more. ASME B16.21 - Nonmetallic Flat Gaskets for Pipe Flanges.
- Semi-metallic gasket - Made from both non-metallic and metallic materials and can operate at both high temperature and pressure applications. They can be used with raised face, male and female, and tongue and groove flanges, and many sizes and styles. ASME B16.20 - Metallic Gaskets for Pipe Flanges: Ring-Joint, Spiral-Wound, and Jacketed
- Metallic gasket - Made from a combination of materials. These gaskets are used for special applications where a tight fit is needed. Ring joint flanges (RJF) often use these gaskets. ASME B16.20 - Metallic Gaskets for Pipe Flanges: Ring-Joint, Spiral-Wound, and Jacketed.
SPIRAL WOUND GASKET
Ring Gaskets and spiral wound gaskets are used with raised face flanges.
FULL FACE GASKET
Full Face Gaskets are used with flat face flanges.
RING JOINT GASKET
Gasket API STAMPING
- Manufactured to standard ASME B16.20 or applicable standard.
- Inner ring material stamp other than carbon steel.
- Outer ring material stamp other than carbon steel.
- Nominal pipe size and pressure class.
- Winding material and filler material.
- Stamping Location
- Metaillac fillers are color coded on full rim of outer ring.
- Non-metallic fillers are marked with color stripes on the outer ring.
- Inner ring material stamped on inner of outter ring.
- Nonmetallic gasket dimensions and tolerances in accordance with ASME B16.21 for ASME B16.5 and ASME B16.47 flanges.
- Standard thicknesses are 1/16" and 1/8", but others are available.
- Spiral wound gaskets for ASME B16.5 1/4" to 24" dimensions and tolerances in accordance with ASME B16.20.
- Spiral wound gaskets for ASME B16.47 22" to 60" Series A (MSS SP-44) dimensions and tolerances in accordance with ASME B16.20.
- Spiral wound gaskets for ASME B16.47 26" to 60" Series B (API Std 605) dimensions and tolerances in accordance with ASME B16.20.
- ASME B16.20 - Metallic Gaskets for Pipe Flanges: Ring-Joint, Spiral-Wound, and Jacketed
- ASME B16.21 - Nonmetallic Flat Gaskets for Pipe Flanges
- ASME B16.47 - Large Diameter Steel Flanges: NPS 26 Through NPS 60 Metric/Inch Standard
- ASME B16.5 - Pipe Flanges and Flanged Fittings: NPS 1/2 through 24
- ISO 4709 - Composition cork -- Gasket material -- Classification system, requirements, sampling, packaging and marking
- ISO 7483 - Dimensions of gaskets for use with flanges to ISO 7005