The function of the cylinder is to provide the pressure space required for the process. It is one of the most important pressure components of the pressure vessel, and its inner diameter and volume often need to be determined by process calculation. Cylindrical cylinders (ie cylinders) and spherical cylinders are the most commonly used cylinder structures in engineering.
When the diameter of the cylinder is small (generally less than 500mm), the cylinder can be made of seamless steel pipe. At this time, there is no longitudinal weld on the cylinder; when the diameter is large, the steel plate can be rolled into a cylinder on the coiling machine or used in a hydraulic press. The upper half is pressed into two semi-cylinders, and the two are welded together by a weld to form a complete cylinder. Since the direction of the weld is parallel to the longitudinal direction (ie, the axial direction) of the cylinder, it is called a longitudinal weld, or simply a longitudinal weld.