Flange Connection Methods

　　Flange connections are an important connection method in pipeline construction.

　　Flange connection methods can generally be divided into five types: slip-on welding, butt welding, socket welding, loose flange, and threaded.

　　The first four are described in detail below:

　　1. Slip-on welding: Only the outer layer is welded, not the inner layer; commonly used in medium and low-pressure pipelines with a nominal pressure below 0.25 MPa. Slip-on welding flanges have three sealing surfaces: smooth, raised face, and tongue and groove, with the smooth type being the most widely used and cost-effective.

　　2. Butt welding: Both the inner and outer layers of the flange are welded; generally used in medium and high-pressure pipelines with a nominal pressure between 0.25 and 2.5 MPa. The sealing surface of butt welding flanges is raised face, making installation more complex, resulting in higher labor, installation, and material costs.

　　3. Socket welding: Generally used in pipelines with a nominal pressure less than or equal to 10.0 MPa and a nominal diameter less than or equal to 40 mm.

　　4. Loose flange: Generally used in pipelines with low pressure but containing corrosive media, these flanges have strong corrosion resistance and are mostly made of stainless steel.

　　This type of connection is mainly used for connecting cast iron pipes, rubber-lined pipes, non-ferrous metal pipes, and flanged valves. Flange connections are also used to connect process equipment to flanges.