Gasket
A gasket is a compressible seal placed between two mating surfaces, most commonly flange faces, to prevent leakage of a fluid under pressure. Bolt load compresses the gasket so that it fills surface irregularities and maintains the seal through pressure and thermal cycling. Non-metallic types include compressed fibre, PTFE and flexible graphite sheet; semi-metallic types include spiral-wound, kammprofile and metal-jacketed gaskets; metallic ring joint gaskets, oval or octagonal, seal in RTJ grooves. Dimensions for pipe flange gaskets are given in ASME B16.20 for metallic and semi-metallic gaskets and ASME B16.21 for non-metallic gaskets, while ring gaskets for wellhead equipment are specified in API 6A. Selection parameters include fluid compatibility, design pressure and temperature, flange class and facing, available bolt load and required tightness. ASME PCC-1 provides guidance on bolted flange joint assembly.
Examples
- Spiral-wound gasket with inner and outer rings for RF flanges
- Octagonal ring joint gasket for API 6A wellhead flanges
- PTFE sheet gasket for corrosive chemical service