If it were technically and economically feasible to manufacture perfectly smooth and polished flanges, and if we could maintain these surfaces in permanent contact, there would be no need for gaskets. This technical and economic impossibility results from:
To overcome these difficulties, gaskets are used as a sealing element between the flange faces. When a gasket is seated between flange surfaces, it "flows", filling the imperfections between them and providing the necessary seal. Therefore, in order to obtain adequate sealing, we must consider four factors: gasket seating stress, sealing force, material selection and surface finish.
We must provide adequate pressure to seat the gasket correctly; so it will be able to flow and fill the flange imperfections. This seating stress must be limited in order to prevent crushing of the gasket by excessive compression.
There must be enough residual pressure on the gasket in order to keep it in sufficient contact with the flange surfaces, thus avoiding leakage.
The gasket material must be able to resist the internal pressure as well as the chemical properties of the fluid to which it is subjected during operation.
There is a recommended flange surface finish for each style of gasket. Surface finish which is not compatible with the gasket is one of the primary causes of leakage.
The Figure 1 shows the major forces in a flanged joint.
Main reasons for gasket failure
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Phone: +49 (0)221/922 342-0
Fax: +49 (0)221/922 342-22
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