Before we talk about Flange Gasket, let’s understand what a gasket is. Here, I would like to go with a universal definition. “A gasket 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.” Yes, that was the definition given in Wikipedia.
Well, that definition covers a lot of details about gaskets. If you are someone who works in the mechanical industry, then you know all of it. Have you heard of “less-than-perfect” mating surfaces? When you want to fix two less-than-perfect surfaces such as two pipelines, then you will need something to fill that less-than-perfect gap. The piece we used for sealing that gap is called a gasket.
Various types of gaskets are there for different purposes. A Flange Gasket is a special type of gasket that is being used for creating a static seal between two flanged surfaces. As mentioned, when you want to fill irregularities between two joining surfaces, you need something that fills the spaces between the joining surfaces. For example, connecting two pipelines that carry oil. Which means – materials used for Flange Gaskets should have the ability to fill gaps between two joining surfaces.
Flange Gasket materials: Non-metallic, semi-metallic, and metallic are the materials being used for manufacturing gaskets. Each type comes with a unique set of properties and advantages/disadvantages. OK, let’s understand each type in details.
* Non-metallic Flange Gaskets: Suitable for low-pressure applications. Manufacturers use composite sheet materials to produce these gaskets. Can be used with raised-face or flat-face flanges. Aramid fiber, elastomer, glass fiber, graphite, and Teflon are the composite materials used for Non-metallic Flange Gaskets manufacturing.
* Semi-metallic Flange Gaskets: Made by combining metal and non-metallic materials. Ideal for high-temperature and high-pressure applications. The metal in the Flange Gasket provides required strength to withstand pressure and temperature while the non-metal provides sealability and conformability. Can be used on tongue-and-groove, raised-face, and male-and-female flanges.
* Metallic Flange Gaskets: Made from one or more metallic materials. Ring-type-joint gasket is another name given for this type. Can be used for high-pressure and high-temperature applications.
Well, we can further divide Flange Gaskets into four categories.
* Sheet gaskets: A simple form of a gasket that comes with or without bolt hole. Also, comes in various sizes, shapes, thickness, and materials.
* Spiral wound gaskets: Same as ring gaskets, can be used for high-pressure applications.
* Corrugated metal gaskets.
* Ring gaskets: This type can be used for extreme high-pressure applications such as off-shore oil/gas pipelines.
Copper Flange Gaskets can be used for ultra-high vacuum systems.
Flange Gasket proper installation:
As mentioned, a gasket is used for filling irregularities between two joining surfaces such as pipelines. Anyway, we humans; make errors when installing gaskets. The most common error is, exerting uneven pressures on the gasket when joining the pipelines by tightening the bolts. Uneven pressure can damage the gasket which leads to leakage. Dirt/dust on the two joining surfaces can cause failures too. With time, bolt tension can decrease gradually due to external factors such as vibration.