The range of structure and use of welding of large diameter flange and butt welding of large diameter flange is different, can show the characteristics and advantages will be different, so when used according to different scope of use, which play an important role in the flange. Steel is large diameter flange, suitable for pressure P is less than or equal to 4MPa occasion; also called high neck flange welding flange, large rigidity, suitable for high temperature pressure. Direct cutting flanges stay inside and outside the processing amount of size and thickness of the disc in the plate, then the bolt hole and processing line. The flange produced in this way is called the cut flange, flange plate with such large diameter width. The process of cutting strips with a medium plate and then rolling into a circle is called a roll, which is used for the production of large flanges. Rolling after the success of the welding process and then flatten, then the waterline and bolt hole. Large diameter flange has common flange and butt welding flange. There is no large diameter threaded flange. In the production and sale of reality, or welding products accounted for much