Gasket, Flange gasket, Gaskets for Flange Connections

A gasket (correct terminology is a “joint” made from “jointing material”) is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression.

A gasket (orange) used as a face seal to prevent flow from escaping from a pipe flange joint.
A gasket (orange) used as a face seal to prevent flow from escaping from a pipe flange joint.

To realize a leak-free flange connection gaskets are necessary.
Gaskets are compressible sheets or rings used to make a fluid-resistant seal between two surfaces. Gaskets are built to operate under extreme temperature and pressures and are available in a wide range of metallic, semi-metallic and non-metallic materials.
The principle of sealing, for example, is the compression from a gasket between two flanges. A gaskets fills the microscopic spaces and irregularities of the flange faces and then it forms a seal that is designed to keep liquids and gases. Correct installation of damage free gaskets is a requirement for a leak-free flange connection.
On this website gaskets ASME B16.20 (Metallic and semi-metallic gaskets for Pipe flanges) and ASME B16.21 (Nonmetallic flat gaskets for pipe flanges) will be defined.
On the Gaskets page you will find more details concerning types, materials and dimensions.

Flange gasket

A flange gasket is a type of gasket made to fit between two sections of pipe that are flared to provide higher surface area.
Flange gaskets come in a variety of sizes and are categorized by their inside diameter and their outside diameter.
There are many standards in gasket for flanges of pipes. The gaskets for flanges can be divided in major 4 different categories:

  1. Sheet gaskets
  2. Corrugated metal gaskets
  3. Ring gaskets
  4. spiral wound gaskets

Sheet gaskets are simple, they are cut to size either with bolt holes or without holes for standard sizes with various thickness and material suitable to media and temperature pressure of pipeline.
Ring gaskets also known as RTJ. They are mostly used in offshore oil- and gas pipelines and are designed to work under extremely high pressure. They are solid rings of metal in different cross sections like oval, round, octagonal etc. Sometimes they come with hole in center for pressure equalization.
Spiral wound gaskets are also used in high pressure pipelines and are made with stainless steel outer and inner rings and a center filled with spirally wound stainless steel tape wound together with graphite and PTFE, formed in V shape. Internal pressure acts upon the faces of the V, forcing the gasket to seal against the flange faces.

Types of gaskets

Materials for gaskets can be divided into three main categories:

  1. Non-Metallic types
  2. Semi-Metallic types
  3. Metallic types

Non-Metallic gaskets are usually composite sheet materials are used with flat-face and raised-face flanges in low Pressure Class applications. Non-metallic gaskets are manufactured from arimid fiber, glass fiber, elastomer, Teflon® (PTFE), graphite etc.. Full-face gasket types are suitable for use with flat-face flanges. Flat-ring gasket types are suitable for use with raised face flanges.
ASME B16.21 covers types, sizes, materials, dimensions, dimensional tolerances, and markings for non-metallic flat gaskets.

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