Sealing with Gaskets

If it were technically and economically feasible to manufacture prefect 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:

• Size of the vessel and/or the flanges.
• Difficulty in maintaining these surfaces perfectly smooth during the handling and/or assembling of the vessel or piping.
• Corrosion or erosion of the surface by time.

To overcome these difficulties, gaskets are used as a sealing element. When a gasket is seated against the flange surface, it flows, filling the imperfections between them and providing the necessary sealing. Therefore, in order to obtain adequate sealing we must consider four factors:

• Seating stress: we must provide an adequate way of seating the gasket so it will be able to flow and fill the flange imperfections. The minimum initial seating stress is recommended by the American Society of Mechanical Engineers (ASME) Pressure Vessel and Boiler Code. This seating stress must be limited in order to prevent the destruction of gasket by an excess of compression.
• Sealing force:  residual stress on the gasket must be maintained, in order to keep it in contact without the flange surfaces, avoiding leakage.
• Material selection: gasket material must resist the pressure as well as the fluid to which it is subjected. Absolute Seal can help you select the right material for your application.
• Surface finish: There is a recommended flange surface finish for each style of gasket and class of service. The use of surface finish not compatible without the gasket is one of the primary causes of leakage.