Based on the connection method, flanges can be divided into the following types:
1. Slip-on Flange (SO): Simple structure, suitable for low-pressure applications (≤PN16). The inner diameter must match the pipe's outer diameter, and welding requires only a single-sided fillet weld.
2. Weld Neck Flange (WN): With an extended neck, suitable for high-pressure applications (PN25-PN100). Welds require 100% radiographic inspection (according to ISO 5817).
3. Socket Weld Flange (SW): The pipe is inserted into the flange and then welded. It is commonly used for small-diameter (DN15-DN50) high-pressure pipelines. The sealing surface is often RF-type.