Type I pressure vessels are usually made of raw material in three different forms of pipe, sheet or ingot. In general, the manufacturing process in all three types consists of two stages. In the first stage, the end part is made together with the cylindrical part of the tank (bottoming treatment) and in the second stage, the necking part is formed (necking treatment).
One of the most important steps in the construction of pressure vessels is hot spinning. In the pipes-produced tanks, seamless steel pipes with heat treatment capability are used.
In the production of the tank made from seamless pipes, the end of the cylinder is formed by spinning. If the cylindrical body needs to be reduced in thickness, the product is also subjected to flow forming treatments. In this method, after heating the end of the cylinder in an induction furnace, the cylinder is carried inside the CNC machine with a carrier and begins to spin. To create local pressure and finally, deformation, the forming roller, moves regularly along a pre-designed path and creates a thickness profile at the end of the pipe, which the end of the pipe is closed finally at the last pass of the forming process. By designing the form and angle of the roller, it is possible to form the end of the pipe into a hemisphere or a lens-shaped shell.
After performing the initial stage of manufacturing the first type of CNG tank, during which the end part is obtained together with the body of the tank, the second stage of the manufacturing process begins to form the necking part of the tank. This process is the same for all cases of producing capsules from the seamless cylinder, sheet, or ingot. To form the necking area, the other end of the capsule needs to be heated by an induction furnace to perform hot work. After generating the necessary heat, the necking profile is created at the end of the capsule with a CNC machine by the process of spinning.