Summary of Classification Methods of Pressure Vessels

2025-05-07

Summary of Classification Methods of Pressure Vessels
A pressure vessel is a sealed container that withstands gas or liquid pressure inside or outside and has high requirements for safety.
Most pressure vessels are cylindrical, with a few being spherical or in other shapes. A cylindrical pressure vessel is usually composed of parts and components such as a cylinder, head, nozzles, and flanges. The higher the working pressure of the pressure vessel, the thicker the wall of the cylinder should be.
Classification of Pressure Vessels
Classification by Pressure Level: Pressure vessels can be divided into internal pressure vessels and external pressure vessels.
Internal pressure vessels can be further divided into four pressure levels according to the design pressure (p), and the specific classification is as follows:
Low-pressure (code L) vessel: 0.1 MPa ≤ p < 1.6 MPa;
Medium-pressure (code M) vessel: 1.6 MPa ≤ p < 10.0 MPa;
High-pressure (code H) vessel: 10 MPa ≤ p < 100 MPa;
Ultra-high-pressure (code U) vessel: p ≥ 100MPa.
Classification by the Role of the Vessel in Production:
Reaction pressure vessel (code R): Used to complete the physical and chemical reactions of the medium.
Heat exchange pressure vessel (code E): Used to complete the heat exchange of the medium.
Separation pressure vessel (code S): Used to complete the fluid pressure balance buffering of the medium and the purification and separation of gases.
Storage pressure vessel (code C, among which the spherical tank is code B): Used to store and contain gases, liquids, liquefied gases and other media.
In a pressure vessel, if it has more than two process action principles at the same time, it should be classified according to the main role in the process.
Classification by Installation Method:
Stationary pressure vessel: A pressure vessel with a fixed installation and use location, and relatively fixed process conditions and operators.
Mobile pressure vessel: When in use, it not only withstands internal or external pressure loads, but also receives the impact force caused by the shaking of the internal medium during the handling process, as well as the external impact and vibration loads brought by the transportation process. Therefore, it has special requirements in terms of structure, use and safety.
The above-mentioned several classification methods only consider a certain design parameter or usage condition of the pressure vessel, and cannot comprehensively reflect the degree of danger of the pressure vessel.
The degree of danger of a pressure vessel is also related to the hazard of the medium and the product of its design pressure p and total volume V. The larger the pV value, the greater the explosion energy when the vessel ruptures, the greater the hazard, and the higher the requirements for the design, manufacture, inspection, use and management of the vessel.
Classification for Safety Technology Management:
The "Regulations on the Safety Technology Supervision of Pressure Vessels" adopts a comprehensive classification method that takes into account both the product of the vessel pressure and volume, the hazard of the medium, and the role of the vessel in the production process, which is conducive to safety technology supervision and management. This method classifies pressure vessels into three categories:
Category III Pressure Vessels. Any of the following situations is a Category III pressure vessel:
High-pressure vessel;
Medium-pressure vessel (only for media with extremely high and high hazard levels);
Medium-pressure storage vessel (only for flammable media or media with a moderate hazard level, and the pV product is greater than or equal to 10MPa·m³);
Medium-pressure reaction vessel (only for flammable media or media with a moderate hazard level, and the pV product is greater than or equal to 0.5Pa·m³);
Low-pressure vessel (only for media with extremely high and high hazard levels, and the product is greater than or equal to 0.2MPa·m³);
High-pressure and medium-pressure shell-and-tube waste heat boilers;
Medium-pressure enameled pressure vessels;
Pressure vessels manufactured from materials with a relatively high strength level (referring to the lower limit of the specified tensile strength in the corresponding standard being greater than or equal to 540MPa);
Mobile pressure vessels, including railway tank cars (media are liquefied gases, cryogenic liquids), tank trucks [liquefied gas transportation (semi-trailer) trucks, cryogenic liquid transportation (semi-trailer) trucks, permanent gas transportation (semi-trailer) trucks] and tank containers (media are liquefied gases, cryogenic liquids), etc.;
Spherical storage tanks (with a volume greater than or equal to 50m³); Cryogenic liquid storage containers (with a volume greater than 5m³).
Cryogenic liquid storage containers (with a volume greater than 5m³)
2. Category II Pressure Vessels. Any of the following situations is a Category II pressure vessel:
Medium-pressure vessel;
Low-pressure vessel (only for media with extremely high and high hazard levels);
Low-pressure reaction vessels and low-pressure storage vessels (only for flammable media or media with a moderate hazard level);
Low-pressure shell-and-tube waste heat boilers;
Low-pressure enameled pressure vessels.
3. Category I Pressure Vessels.

Summary of Classification Methods of Pressure Vessels1746629613901

Low-pressure vessels other than those specified above are Category I pressure vessels.
It can be seen that the classification method of pressure vessels in China comprehensively considers influencing factors such as design pressure, geometric volume, material strength, application occasion, and the hazard level of the medium.
For example, due to the different characteristics of the contained medium or the functions of the vessel, that is, according to the potential hazard level, low-pressure vessels can be classified as Category I, Category II or even Category III pressure vessels. Note: In the table, P represents the design pressure, and V represents the geometric volume of the pressure vessel.
I. Classification by Design Pressure:

Low-pressure (L): 0.1MPa ≤ P < 1.6 MPa
Medium-pressure (M): 1.6 MPa ≤ P < 10 MPa
High-pressure (H): 10 MPa ≤ P < 100 MPa
Ultra-high-pressure (U): P ≥ 100 MPa
II. Classification by the Role in the Process:
Reaction pressure vessel (R): Mainly used to complete the physical and chemical reactions of the medium. Such as reactors, reaction kettles, decomposition pots, vulcanizing tanks, decomposition towers, polymerization towers, high-pressure kettles, ultra-high-pressure kettles, synthesis towers, converters, cooking pots, steaming balls, autoclaves, gas generators, etc.
Heat exchange pressure vessel (E): Mainly used to complete the heat exchange of the medium. Such as shell-and-tube waste heat boilers, heat exchangers, coolers, condensers, evaporators, heaters, sterilization pots, dyeing machines, drying cylinders, steaming and frying pans, preheating pots, solvent preheaters, steamers, steam stripping machines, electric steam generators, water jackets of gas generators, etc.
Separation pressure vessel (S): Mainly used to complete the fluid pressure balance buffering of the medium and the purification and separation of gases, etc. Such as separators, filters, oil collectors, buffers, scrubbers, absorption towers, copper washing towers, drying towers, stripping towers, steam headers, deaerators, etc.
Storage pressure vessel (C, among which the spherical tank is B): Mainly used to store and contain gases, liquids, liquefied gases and other media, such as various types of storage tanks.
III. Comprehensive Classification:
Stationary pressure vessels: They are used in a fixed environment and cannot be moved. The working media are diverse, and most of them are various chemical dangerous goods that are toxic, flammable, explosive and corrosive. Such as spherical storage tanks, horizontal storage tanks, various heat exchangers, synthesis towers, reactors, dryers, separators, shell-and-tube waste heat boilers, manned containers (such as medical oxygen chambers), etc.
Mobile pressure vessels: They are mainly used during movement and are packaged as a certain medium and carried on a means of transportation. Many of the working media are flammable, explosive or toxic. Such as the tanks of automotive and railway tank cars.
Cylinder-type pressure vessels: As a type of pressure vessel, there is a very large number of them in society. There are high-pressure cylinders (such as hydrogen, oxygen, and nitrogen cylinders) and low-pressure cylinders (such as civil liquefied petroleum gas cylinders). Many of the working media are also flammable, explosive or toxic substances. They also have strong mobility, with both long-distance movement during transportation and short-distance movement during specific use. Such as liquefied petroleum gas cylinders, oxygen cylinders, hydrogen cylinders, nitrogen cylinders, carbon dioxide cylinders, liquid chlorine cylinders, liquid ammonia cylinders, and dissolved acetylene cylinders, etc.
IV. Safety Accessories of Pressure Vessels:
Safety valve: The function of the safety valve is to automatically open when the pressure in the equipment exceeds the specified requirement, release the excess pressure, and bring the equipment back to the normal working pressure state. After the pressure returns to normal, the safety valve closes automatically.
After the safety valve is calibrated, it is strictly prohibited to use means such as adding heavy objects, moving the weight hammer, and jamming the valve disc to arbitrarily increase the setting pressure of the safety valve or make the safety valve ineffective.
Pressure gauge: The measuring range of the pressure gauge should be suitable for the working pressure of the equipment, usually 1.5 to 3 times the working pressure, preferably 2 times. A red line should be drawn on the dial of the pressure gauge to indicate the maximum allowable working pressure. There should be no water leakage or steam leakage in the connecting pipe of the pressure gauge, otherwise, the indicated value of the pressure gauge will be reduced.
Rupture disc
Thermometer
Level gauge
Pressure reducing valve
Emergency shut-off device: Its function is to close the valve urgently and cut off the gas source quickly when the pipeline and its accessories are ruptured, there is misoperation, or a fire accident occurs near the tank truck, to prevent the accident from spreading and expanding.
Safety interlock device for quick-opening pressure vessels: The safety interlock alarm device for quick-opening is an effective measure to prevent operational accidents of quick-opening pressure vessels. Its functions are:
a. The interlock control function that the pressure vessel can only be pressurized and operated when the quick-opening door reaches the predetermined closed position;
b. The interlock linkage function that the quick-opening door can only be opened after the internal pressure of the pressure vessel is completely released and the safety interlock device is disengaged;
c.
It has an alarm function synchronized with the above actions.