Gasket and its classification according to design, types and essential properties of gasket

Gasket and its classification according to design, types and essential properties of gasket _________________________________________________________________________

Gasket is a mechanical seal that fills the space between two or more mating surfaces, generally to prevent leakage under compression from or into jointed objects.

Gaskets are generally made from sheets of flat material such as paper, rubber, silicone, metal cork, felt, neoprene, nitrile rubber, fibreglass, polytetrafluoroethylene or a plastic polymer.

In pipes, the gasket is a sealing material placed between the connecting flanges to produce a static seal which, under all operating conditions, preserves the leak-proof seal. Various types of gaskets are used to achieve leak-proof sealing between the flanges of the tubing.

Classification According To Design Of Gasket  Sheet Gaskets when a sheet of material has the "punched out" shape of a gasket, it is a sheet gasket. This could lead to a crude, quick and cheap gasket. The non-asbestos gasket sheet is longlasting, of multiple materials and thick. Examples of materials are coal, carbon or nitrile synthetic rubber. Products using sheet gaskets include acids, corrosive substances, steam or mild caustics.

During the installation of a sheet gasket flexibility and good recovery prevent breakage.  Solid Material Gaskets - The principle behind solid material is to use metals that can not be cut out of sheets but are still cheap to produce.

Such gaskets usually have a much higher level of quality control than sheet gaskets and can typically withstand much higher temperatures and pressures.

 Spiral-Wound Gaskets - The sealing element of the spiral wound gasket is created by interlacing the plies of the alternating metal winding strip with the filler material. The metal strip formed in the key seal element of this type of semi-metallic gasket. The filler material in these gaskets acts as a sealing element, and the metal provides structural support.  Constant Seating Stress gaskets - Constant seating stress gaskets derive their name from the fact that the carrier ring profile takes into account the rotation of the flange (deflection under preloading of the bolt Constant seating stress gasket consists of two components; a solid carrier ring of stainless steel, and two sealing elements of some compressible material mounted in two opposite channels; one channel on either side of the carrier ring.  Kammprofile Gaskets Kammprofile gaskets are manufactured by adding a sealing layer in non-metallic materials (such as graphite, PTFE-Teflon, ceramic

fibres, non-asbestos, Mica, etc.) or metallic materials (such as aluminium or silver) on either side of a metal core with 1 mm Cam-Pitch concentric grooves.., petrochemical, power generation and nuclear installations (to seal flanges, heat exchangers, superheaters and, other pressure equipment) this all industries make use of kammprofile gaskets  Fishbone Gaskets - Fishbone gaskets are direct substitutes for Kammprofile and Spiral wound gaskets. They are fully CNC machines made of similar materials, but the design of the gaskets has eliminated the inherent shortcomings. Fishbone gaskets are not unwinded in storage or in the plant The rounded edges do not cause damage to the flange. The added "Stop Step" prevents the Fishbone gaskets from being over compressed/crushed, often caused by hot torque techniques on plant start-up.  Flange gasket - The flange gasket is a type of gasket made to fit between two sections of the pipe which are flared to provide a higher surface area. Flange gaskets come in a variety of sizes and are categorized by their inner diameter and outer diameter.

Types of Gasket: Metallic, Semi-Metallic, Non- Metallic 

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Metallic Gaskets - Metallic gaskets can be constructed in a variety of shapes and sizes recommended for use in highpressure / temperature applications. Such gaskets need much higher sealing surface quality than non-metallic gaskets. Except for weld ring gaskets, high loads are required for the seat of metallic gaskets, as they rely on the deformation or coining of the material on the flange surfaces. Examples include ring joints, lens rings, weld rings, solid metal gaskets, etc. materials, dimensions, dimensional tolerances, and markings for metallic and semi-metallic gaskets are covered under standard ASME B16.20.

Semi-Metallic – Semi-metallic gaskets are made of both metallic and non-metallic materials. The metal provides the strength and resilience of the gasket, while the non-metallic component provides the conformable sealing material. Such gaskets are ideal for applications with low and high pressure and temperature. There is a wide variety of materials available. Examples include spiral wound gaskets, coated metal core gaskets, metal jacketed gaskets, metal-reinforced gaskets, etc. ASME B16.20 covers materials, dimensions, dimensional tolerances and markings for metallic and semimetallic gaskets.

Non-Metallic – Non Metallic gaskets are usually composite sheet materials which are used in low to medium pressure services. With careful selection, these gaskets are not only suitable for general service but also extreme chemical services and temperatures. The most common materials used for this type of gasket are Graphite, Rubber, Teflon,

PTFE and Compressed Non-Asbestos Fiber (CNAF). Such gaskets are also known as soft gaskets.

Essential Properties of Gasket 1. Water-resistance – The gasket must not be porous to the fluid being sealed.

2. Compressibility – To create the initial seal, the gasket should compress into the flange sealing faces imperfections.

3. Stress Relaxation –The gasket should not show significant flow (Creep) when subjected to load and temperature. This flow would allow the bolts to relax, reduce the stress on the surface of the gasket and cause leakage.

4. Flexibility–Although normally stable, under the influence of cycling temperature and pressure, the flanges move slightly relative to each other. The gasket should be capable of compensating for such movements.

5. Chemical resistance–The gasket should be able to withstand a chemical attack from the process medium being handled. Similarly, the gasket material itself must not contaminate the process medium.

6. Temperature tolerance–The gasket should be able to withstand the effects of higher and lower temperatures in the process and external atmospheric temperatures.

7. Anti-stick – The gasket must be easily removed after use.

8. Anti-corrosion – The gasket must not cause the faces of the flange to corrosion.

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