GOST 12820-80 FLANGE tells you that butt welding flange with a neck, the sealing surface of butt welding flange with the neck is: raised surface (RF), concave surface (FM), convex surface (M), tenon surface (T), groove face (G), full plane (FF). GOST 12820-80 FLANGE tells you that its advantages are that the connection is not easily deformed, the sealing effect is good, and it is widely used.

GOST 12820-80 FLANGE tells you that it is suitable for pipelines with large fluctuations in temperature or pressure or pipelines with high temperature, high pressure, and low temperature, as well as pipelines for transporting expensive media, flammable and explosive media, and toxic gases.
its downsides. GOST 12820-80 FLANGE tells you that butt welding flanges with necks are bulky, heavy, expensive, and difficult to install and position. Therefore, it is easier to bump during transportation.
The above information is the GOST 12820-80 FLANGE manufacturer's introduction and analysis of the classification of the flange, hope it helps you.