Plate type flat welding flange (chemical standard HG20592, national standard GB/T9119, mechanical JB/T81): easy to obtain materials, simple to manufacture, low cost, and widely used; However, due to its poor rigidity, it should not be used in chemical process piping systems with supply and demand, flammability, explosiveness, and high vacuum requirements, as well as in highly hazardous environments. The sealing surface types include flat and protruding surfaces.