Stainless steel four-way has the same diameter and different diameter, the diameter of the four-way pipe joint ends are the same size; different diameter four-way main pipe joints the same size, and the branch pipe size is smaller than the main pipe size. A stainless steel spool is a type of pipe used at the branch of a pipeline. For the production of four-way seamless pipe, the current commonly used processes are hydraulic bulging and hot-pressing. a. Hydraulic bulging The four-way hydraulic bulging is a forming process where the branch pipe is expanded by the axial compensation of the metal material. In the process, a special hydraulic press is used to inject liquid into the tube with the same diameter as the four-way tube. The tube is squeezed by the two horizontal cylinders of the hydraulic press. The tube is squeezed and its volume becomes smaller. The pressure of the liquid increases as the volume of the tube becomes smaller. When the required pressure of the four-way branch tube is reached, the metal material flows along the inner cavity of the mold under the double action of the liquid pressure in the side cylinder and the tube tube to swell the branch tube. The four-way hydraulic bulging process can be formed at one time, resulting in higher production efficiency; the four-way head and shoulder wall thicknesses are all increased. Due to the large tonnage of equipment required for the seamless four-way hydraulic bulging technology, it is currently used for the manufacture of standard wall thickness four-pass smaller than DN400. The suitable forming materials are low-carbon steels, low-alloy steels, and stainless steels that have relatively low tendency to cold hardening, including some non-ferrous metal materials such as copper, aluminum, and titanium. b. Hot press forming Four way hot press forming is to make the tube blank larger than four-way diameter flattened to the size of four-way diameter, and open a hole in the part of the stretching branch tube; the tube blank is heated and put into the forming die , And in the tube filled with the die of the tensile branch; under pressure, the tube is radially compressed, in the process of radial compression, the metal flows in the direction of the branch and forms a branch under the stretching of the die. The entire process is formed by the radial compression of the tube and the stretching process at the branch. Different from the hydraulic bulging four-way pipe, the metal of the hot-pressed four-way branch pipe is compensated by the radial movement of the pipe blank, so it is also called a radial compensation process. Due to the use of heated post-pressing, the tonnage of the equipment needed to form the material is reduced. Hot-pressed crosses have a wide adaptability to materials and are suitable for low-carbon steels, alloy steels, and stainless steels. Especially for large-diameter and thick-walled pipes, this forming process is usually used.