Weld neck flange refers to a flange with a tapered neck and butt welding with the cylinder or pipe. It is an integral flange. Due to the transition structure of the taper neck and butt welding connection, the strength and rigidity of the flange are enhanced, and the sealing performance is better than that of the flat welding flange. The disadvantage is that it needs to be made with forgings, which consumes a lot of materials and costs a lot. Suitable for occasions with high pressure, high temperature or high sealing requirements.