Structural requirements that should be met in the manufacture of pressure vessels: strength. The dimensions of all parts of the pressure vessel should be calculated and determined according to relevant regulations to ensure sufficient strength. Stiffness is the ability of a component to retain its original shape under external force. If the stiffness is insufficient, instability will occur. Therefore, the size of some components of the heavy oil catalytic cracking unit is often determined by the stiffness. Durability generally refers to the required service life of the pressure vessel. Sealing, many of the materials in the pressure vessel are flammable, explosive or toxic substances. If they leak out, it will not only cause waste of materials, but more importantly, it will poison the operator and even cause an explosion. Therefore, the sealing performance of the pressure vessel is also an important issue related to whether it can ensure safe operation.