Q215/A573 Welded steel pipe used for welding steel pipe is steel plate or strip steel, which is divided into furnace welded pipe, electric welding (resistance welding) pipe and automatic arc welding pipe because of its different welding process. Because of its different welding forms are divided into straight seam welded pipe and spiral welded pipe two kinds. Because of the shape of its end, it is divided into circular welded pipes and special-shaped (square, flat, etc.) welded pipes.