A flat welding flange refers to a type of flange that is connected to vessels or pipes using angular welds. It belongs to the type of flanges without a fixed shape. During design, it is verified as a solid flange or a loose flange based on the degree of integration between the flange ring and the cylindrical section. Flange rings come in two types: with a neck and without a neck. Compared to neck welding flanges, flat welding flanges have a simpler structure and require less material, but they have lower stiffness and sealing performance. Flat welding flanges are widely used in the connection of medium and low-pressure vessels and pipes.