Flat welding flanges are suitable for connecting steel pipes with a nominal pressure not exceeding 2.5MPa. The sealing surface of flat welding flanges can be made into three types: smooth, concave convex, and tenon groove. Smooth flat welding flanges are the most widely used. It is often used in situations where the medium conditions are relatively mild, such as low-pressure non purified compressed air and low-pressure circulating water.