Gasket & its Types

 Gasket:

The purpose of any Gasket is to connect piping systems in such a manner as to produce a leak free environment. Using a gasket material softer than two adjoining flanges is an excellent way to eliminate the possibility of a fluid escape. Gaskets can be made of materials such as asbestos, rubber, neoprene, teflon, lead or copper.

Selection of gasket depends upon the following factors:

• Compatibility of the gasket material with the fluid.
• Ability to withstand the pressure - temperature of the system.

Types of Gaskets:

There are three types of gaskets used in process piping.

• Non-Metallic
• Composite
• Metallic

1) Non-Metallic Gasket:

• It is the least expensive and most common type and is used only for 150# rating. These gaskets are also known as a Soft gasket.
• The most common materials used for this type of gaskets are Graphite, Rubber, Teflon, PTFE, and Compressed Non-Asbestos Fiber (CNAF)
• Flat ring gasket are used with raised face flanges.
• Full face gaskets are used with flat ring face flanges.
• Non metallic gasket are manufactured to dimensional standard ASME B16.21.

2) Composite Gasket:

• Composite gaskets are a combination of metal and non-metal material. Different types of combinations of materials are possible based on the service requirement.
• Spiral wound, Metal Jacketed, and Cam profile gasket are well known in the composite gasket category. They are used in a wide range of pressure and temperature services.
• Composite gaskets are cost effective compare to metal gaskets but Careful handling is required.
•  Composite gaskets are used on raised face, male-female, and tongue-and-groove flanges.

• i) Spiral Wounded Gasket:

• The metal strip is usually 55304, but other materials can also be used for corrosion resistance depending on the fluid.
• They are manufactured from a thin V-shaped metal strip and a strip of gasketing material wound into a ring.
• Spiral wound gaskets are provided with carbon steel external ring known as centering ring, which helps in positioning the gaskets between the two flanges.  For critical services, an internal ring is also provided to avoid over compression of the gaskets.  The internal ring material should be suitable for the service fluid.
• Spiral wound gaskets are covered under standard ASME B 16.20

• ii) Cam Profile Gasket:

• Cam profile Gasket is having a solid metal core with concentric grooves. Filler material, either graphite or PTFE is layered on this grooved metal ring. 
• It is Costlier than Spiral wound gasket but provides better blowout resistance and easy to handle even in large diameters.
• Cam profile gaskets are used in a wide variety of service fluids and operating pressure-temperatures classes from Class 150 to Class 2500 flanges.

• iii) Metal Jacketed Gasket:

• In Metal Jacketed Gasket, the Soft filler material is enclosed in a thin sheet of a metal jacket.
• Jacketed gaskets are easily fabricated in a variety of sizes and shapes. 
• They are used in heat exchangers, shell, channel, and cover flange joints. It also used in valves’ body bonnet joint.

3) Metallic-Ring Gasket:

• Ring joint gaskets are used with Ring type joint flanges for high pressure services, normally 900# and above.
• These gaskets have either octagonal or oval cross section; however octagonal type is preferred because of its larger contact area with the flange groove.
• The material of the gaskets should be suitable for the service fluid.
• Their hardness should be less than that of the material flanges to assure a tight joint.
• Ring joint gaskets are covered under standard ASME B16.20