In piping, a Gasket is sealing material placed between connecting flanges to create a static seal. This will maintain the leakage-proof sealing in all operating conditions. Different types of gaskets are used to achieve leak proof sealing between the pipe flange.
The primary function of gaskets is to seal the irregularities of each face of the flange so that there will be no leakage of the service fluid from the flange joint.
Types of Gaskets
There are three types of gaskets used in process piping.
- Non-Metallic
- Metallic
- Composite
Non-Metallic Gasket
The most common materials used for this type of gaskets are Graphite, Rubber, Teflon, PTFE, and Compressed Non-Asbestos Fiber (CNAF). These gaskets are also known as soft gaskets. It can be full face or inside bolt circle type.
- Non-Metallic gaskets can easily compress with low tension bolting
- These types of gaskets are used with low-pressure class flanges such as 150 and 300 Class and also in low-temperature However, graphite gasket can be used up to 500 Degree centigrade.
- Rubber and elastomer gaskets are not used in hydrocarbon services but used in utility lines.
- Non-Metallic gaskets are the cheapest and most easily available
Full-face gasket types are suitable for flat-face (FF) flanges. Flat ring gasket types are suitable for use with raised-faced (RF) flanges.
You can see in the right-side image a full-face gasket, and the left side is inside the bolt circle gasket. The image also shows CNAF & PTFE gaskets. Full face gasket can only be used with FF flange and is normally used for temporary connection of utility lines.
Metal Gasket / Ring Joint Gasket / RTJ Gasket
Metal gaskets are manufactured from a material such as Soft iron, Low Carbon steel, Stainless Steel, Monel, and Inconel. These gaskets are also known as ring gaskets or RTJ gaskets.
- Metallic gaskets are used in high-pressure class flanges, normally above 900 Class; they can also be used for high-temperature
- High tension bolting is required when we use metallic gaskets.
- They are very robust & most costly.
The RTJ Gasket fits in a groove machined on the flange face of both mating flanges. Two types of the metallic gasket are used with RTJ flange Octagonal and Oval. You can see the difference in their cross-section view.
Composite Gasket or Semi-Metallic
Composite gaskets are a combination of metal and non-metal materials. Different types of combinations of materials are possible based on the service requirement.
Spiral wound, Metal Jacketed, and Kamprofile 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 compared to metal gaskets, but Careful handling is required. Composite gaskets are used on raised faces, male-female, and tongue-and-groove flanges.
Spiral Wound Gasket
The most widely used composite type gasket is a Spiral Wound Gasket. It is suitable for a wide range of pressure and temperature class. Normally Graphite or PTFE is used as filler material & stainless steel or other exotic material is used as the winding material.
There are three components in the spiral wound gasket. Inner & Outer ring, filler material, and winding material. However, sometimes an inner ring is not used. You can see in the image a spiral wound gasket with and without an inner ring.
The inner ring is used to provide additional support to the winding material. The winding is an alternative layer of filler material and winding material. The filler material is a soft material such as graphite and PTFE, and the winding material is a thin sheet of metal.
Kammprofile / Campofile Gasket
Kamm/ 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 the Spiral wound gasket but provides better blowout resistance and is easy to handle even in large diameters.
Kammprofile gaskets are used in a wide variety of service fluids and operating pressure-temperatures classes from Class 150 to Class 2500 flanges.
Metal Jacketed Gasket
In Metal Jacketed Gasket, the Soft filler material is enclosed in a thin sheet of a metal jacket. There are different ways to cover filler material, as shown in the image.
Jacketed gaskets are easily fabricated in a variety of sizes and shapes. They are used in heat exchangers, shells, channels, and cover flange joints. It is also used in valves’ body bonnet joints.
Flange Gasket Material
How to pick the ideal gasket for a piping application? To choose the suitable flange gasket material, piping engineers need to consider the following four vital variables: liquid kind, process temperature/pressure, fugitive emissions Laws, and other general considerations. While gaskets are relatively affordable components of the total piping system, they are essential for its integrity and integrity: conserving a couple of dollars with gaskets might produce more significant disasters in the mid-long term; take care!
