What are pressure vessels?

A pressure vessel is a sealed container that is subjected to gas or liquid pressure from within or outside, and requires high standards in terms of safety. Pressure vessels are mainly cylindrical, with a few being spherical or of other shapes. Cylindrical pressure vessels are typically composed of components such as the cylinder body, end caps, nozzles, and flanges. The higher the operating pressure of the pressure vessel, the thicker the walls of the cylinder body need to be. Classification of pressure vessels: Classified by pressure level, pressure vessels can be divided into internal pressure vessels and external pressure vessels. Internal-pressure vessels can also be classified into four pressure grades based on their design pressure (p), as follows: Low-pressure (code L) vessels: 0.1 MPa ≤ p < 1.6 MPa; Medium-pressure (code M) vessels: 1.6 MPa ≤ p < 10.0 MPa; High-pressure (code H) vessels: 10 MPa ≤ p < 100 MPa; Ultra-high-pressure (code U) vessels: p ≥ 100 MPa. Classified by the role of the container in production: Reaction pressure vessels (code R): used to carry out physical and chemical reactions of substances. Heat exchange pressure vessel (code E): used to facilitate heat exchange of fluids. Separation pressure vessel (code S): used for achieving fluid pressure balance and buffering, as well as gas purification and separation. Storage pressure vessels (code C, with spherical tanks coded as B): used for storing gases, liquids, liquefied gases, and other such substances. In a pressure vessel, when it possesses two or more process operation principles simultaneously, the types should be classified according to the primary function in the process. Classified by installation method: Fixed-pressure vessels are those that have a fixed location for installation and use, with relatively fixed process conditions and operators as well. Mobile pressure vessels: When in use, they are subjected not only to internal or external pressure loads, but also to impact forces caused by the movement of the fluid inside them during transportation. In addition, they face external impacts and vibration loads during transport; as a result, they have specific requirements in terms of structure, operation, and safety. The classification methods mentioned above take into account only certain design parameters or operating conditions of pressure vessels, and cannot comprehensively reflect the degree of risk associated with them. The degree of danger associated with pressure vessels is also related to the hazard of the medium, as well as the product of its design pressure p and total volume V. The higher the pV value, the greater the explosive energy released in the event of vessel rupture, and the greater the risk; this implies stricter requirements for the design, manufacturing, inspection, use, and management of such vessels. Classified by safety technology management: The \"Regulations on Safety Technology Supervision of Pressure Vessels\" adopts a comprehensive classification method that takes into account both the product of the vessel’s pressure and volume, as well as the hazard level of the medium and the role of the vessel in the production process, thereby facilitating safety technology supervision and management. This method classifies pressure vessels into three categories: 1. Category III pressure vessels are those that fall under one of the following conditions: high-pressure vessels ； Medium-pressure vessels (only for media with extremely high and high toxicity) ； Medium-pressure storage vessels (only for flammable or moderately hazardous media with a pV product of 10 MPa·m3 or greater) ； Medium-pressure reaction vessel (only for flammable or moderately hazardous media with a pV product of 0.5 Pa·m3 or greater) ； Low-pressure vessels (only for media with extremely high or high toxicity levels, and a product of at least 0.2 MPa·m3) ； High-pressure and medium-pressure shell-and-tube waste heat boilers ； Medium-pressure glass-lined pressure vessel ； Pressure vessels manufactured from materials with a high strength level (meaning that the minimum specified value for tensile strength in the relevant standards is 540 MPa or higher) ； Mobile pressure vessels, including railway tank cars (for liquefied gases and cryogenic liquids), tank trucks, and tank containers (for liquefied gases and cryogenic liquids), etc ； Spherical storage tank (volume ≥ 50 m3) ； Low-temperature liquid storage containers (capacity greater than 5 m3). Low-temperature liquid storage containers (with a volume greater than 5 m3). 2. Pressure vessels of Category II: Such vessels are considered to be of Category II if they meet one of the following conditions: medium-pressure vessels ； Low-pressure vessels (only for media with extremely high and high toxicity) ； Low-pressure reaction vessels and low-pressure storage vessels (only for flammable media or media with moderate toxicity) ； Low-pressure shell-and-tube waste heat boiler ； Low-pressure glass-lined pressure vessels. 3. Class 1 pressure vessels: Low-pressure vessels other than those specified above are classified as Class 1 pressure vessels.

Those that meet the 150 criterion are considered pressure vessels, while those that meet the relevant classification criteria are regarded as pressure vessels subject to supervision and inspection. Generally, vessels with an operating pressure greater than 1 bar, those with a gas phase space, or those handling media at temperatures above their boiling point fall into this category

The original poster can search for similar posts, or refer to the standards themselves; over time, they will gradually understand it. There is no need to elaborate on this issue anymore.