The spool is a kind of pipe fitting used at the branch of the pipeline. The spool is divided into equal diameter and different diameter. The ends of the equal diameter spools are all the same size; The size of the nozzle of the branch pipe is smaller than that of the main pipe. For the use of seamless pipes to manufacture spools, there are currently two commonly used processes: hydraulic bulging and hot pressing. The efficiency is high; the wall thickness of the main pipe and the shoulder of the spool are increased. Due to the large tonnage of equipment required for the hydraulic bulging process of the seamless spool, the applicable forming materials are those with relatively low cold work hardening tendency.