The butt welding flange is not easy to deform, has good sealing and is widely used. It has corresponding rigidity and elasticity requirements and reasonable butt welding thinning transition. The distance between the welded junction and the joint surface is large, and the joint surface is free from welding temperature deformation. It adopts a complex trumpet shape structure, which is suitable for pipelines with large fluctuation of pressure or temperature or pipelines with high temperature, high pressure and low temperature, It is generally used for the connection of pipes and valves with PN greater than 2.5MPa; It is also used for pipelines conveying expensive, flammable and explosive media.