BUTT-WELDING FLANGE is not easy to deform, well-sealed, widely used, there are corresponding requirements of rigidity and elasticity and reasonable transition of thinning in butt welding, the distance between the welding joint and the joint is large, and the joint is free from deformation of welding temperature, apply to the pressure or temperature fluctuations of the pipeline or high-temperature, high-pressure and low-temperature pipeline, generally used for PN greater than 2.5 MPA pipe and valve connection; also used for conveying expensive, flammable, explosive medium pipeline.