Its diameter problems generally occur in small diameter (less than DN32) straight pipes and (less than DN65) three-way elbows; for example, if you specify a diameter of DN25, then you cannot use DN25 steel pipes when selecting steel pipes. You need to use DN32 steel pipes. Only by welding with DN25 flange can the diameter be guaranteed. The same principle of DN25 elbows or tees needs to be selected and welded to a level of pipe, that is, DN32 diameter and DN25 flanges for group welding. The larger type of steel pipe is used to better ensure the original diameter of the flange. Is to ensure the connection.