Butt welded flange, also known as high neck flange, is rigid and suitable for high pressure and temperature occasions. There are three types of flange sealing surface: flat sealing surface, which is suitable for situations with low pressure and non-toxic medium; concave and convex sealing surface, which is suitable for situations with slightly higher pressure; mortise sealing surface, which is suitable for situations with flammable, explosive, toxic medium and high pressure. Gasket is a kind of ring which can produce plastic deformation and has certain strength. Most gaskets for butt-welded flanges are cut from non-metallic plates or manufactured by professional factories on a regular scale. The data are asbestos rubber sheets, asbestos sheets, polyethylene sheets, etc. There are also metal-clad gaskets made by wrapping asbestos and other non-metallic materials with thin metal sheets.