Pressure vessel refers to sealed equipment which is used for holding gases or liquids and can bear a certain pressure. Pressure vessels are classified in many methods, with the following classes in usage, manufacturing and inspection. A. Pressure level: low-pressure vessel, medium-pressure vessel, high-pressure vessel and ultra-high-pressure vessel B. Contained media: noncombustible, non-toxic; inflammable or poisonous; highly toxic C. Different actions of technological processes: a. Reaction vessel: be used for completing physical and chemical reactions of media b. Heat exchanging vessel: be used for completing heat exchange of media c. Separation vessel: be used for completing mass exchanging, gas purification as well as solid, liquid and gas separation of media d. Storage and transportation vessel: be used for holding liquids or gas materials, storing and transporting media or achieving a balanced buffering effect on the pressure.