What is pressure vessel?
Pressure vessel, which holds a gas or liquid and carries a certain pressure, is a closed device.
Pressure vessel is a
closed container that can withstand pressure. The use of pressure vessels is extremely wide, it has an important position and role in many sectors of industry, civil, military, and many areas of scientific research. Among them, the chemical industry and petrochemical industries with the most, only in the petrochemical industry in the application of pressure vessels accounted for about 50 % of the total number of pressure vessels. Pressure vessels in the chemical and petrochemical fields, mainly for heat transfer, mass transfer, reaction, and other processes, as well as storage, and transportation of pressurized gas or liquefied gas; in other industrial and civil fields also have a wide range of applications, such as air compressors. Various special compressors and refrigeration compressor auxiliary equipment (coolers, buffers, oil-water separators, gas storage tanks, evaporators, liquid coolant storage tanks, etc.) are
pressure vessels.
Structure of pressure vessel
The housing of various chemical equipment is a kind of container, it has to withstand the pressure, temperature, and chemical media in the chemical process, the machine and equipment to work for a long time, in addition to economic considerations. Pressure vessel technology is the integration of applied mechanics, materials science, metallurgical processes, mechanical manufacturing processes, technical physics, and other information, specializing in the use of pressure vessels for chemical production.
The structure of the pressure vessel is usually characterized by the shell, head, receiver, seal, support, and other components. The material is mostly steel, and the production method is mainly pressure processing and welding.
Range of pressure vessels
High working pressure (pw) greater than or equal to 0.1MPa (excluding liquid static pressure, the same below); internal diameter (non-circular cross-section refers to its large size) greater than or equal to 0.15m, and capacity (V) greater than or equal to O.03m³; holding medium for gas, liquefied gas or a high ambient temperature higher than or equal to the standard boiling point of the liquid.
Manufacturing process of pressure vessel
Pressure vessel manufacturing process can generally be divided into raw material acceptance process, scribing process, cutting process, rust removal process, machining (including edge planing, etc.) process, rolling process, grouping process, welding process (product welding test plate), nondestructive testing process, opening scribing process, the total inspection process, heat treatment process, pressure test process, anti-corrosion process.
Different welding methods have different welding processes. The welding process is mainly based on the material, grade, and chemical composition of the welded workpiece, the type of structure of the welded parts, and welding performance requirements to determine. First of all, to determine the welding method, such as hand arc welding, submerged arc welding, tungsten arc welding, melting electrode gas shielded welding, etc. There are very many types of welding methods that can only be selected on a case-by-case basis. After determining the welding method, and then developing the welding process parameters, welding process parameters vary, such as hand-arc welding mainly includes welding rod type (or brand), diameter, current, voltage, welding power source type, polarity connection, the number of layers of welding, the number of channels, inspection methods and so on.
Type of pressure vessel
Pressure vessels are classified in many ways, from the use, manufacture, and supervision of the classification, there are the following.
| Type | Description |
| Grades of pressure bearing | Low-pressure vessels, medium-pressure vessels, high-pressure vessels, and ultra-high-pressure vessels. |
| Containing medium | Non-flammable, non-toxic; flammable or toxic; highly toxic. |
| Different roles in the process | Reaction vessel is used to complete the physical and chemical reactions of the medium.
Heat exchange vessel is used to complete the heat exchange of the medium.
Separation vessels are used to complete the mass exchange of media, solid, liquid, gas purification, and gas separation of containers.
Storage and transportation containers are used to hold liquid or gas materials, storage media, or pressure to play a balancing buffer role in the container. |
Multi-chamber pressure classification
Multi-cavity pressure vessels (such as heat exchangers and shell process, jacketed vessels, etc.) in accordance with the category of the high-pressure cavity as the category of the vessel and according to the category of use management. But each pressure cavity should be in accordance with the respective categories of design, and manufacturing technology requirements. The pressure cavity for the category delineation, design pressure to take the design pressure of the pressure cavity, and the volume to take the geometric volume of the pressure cavity.
Classification of multiple media vessels in the same cavity
A pressure cavity with a variety of media, according to the group of high media classification.
Media content of very small container classification
When a hazardous substance in the medium content is very small, should be considered by the degree of harm and its content, and the pressure vessel design unit to decide on the media group.
Species classification
In a pressure vessel, if more than two process role principles are at the same time, should be divided into varieties according to the main role in the process.
The specific division is as follows.
Reaction pressure vessel
Reaction pressure vessel is mainly used in industry to complete physical and chemical reactions in media pressure vessels.
Heat exchange pressure vessel
Heat exchange pressure vessel is mainly used to complete the medium of heat exchange pressure vessels, such as shell and tube waste heat boilers, heat exchangers, coolers, condensers, heaters, sterilization pot, dyeing apparatus, drying cylinder, steam frying pan, preheating pot, solvent preheater, steam pot, steam off the machine, electric steam generator, gas generator water jacket, etc.
Separation pressure vessel
Separation pressure vessel is mainly used to complete the medium of fluid pressure balance buffer and gas purification and separation of pressure vessels, such as separators, sub-vapor cylinders, filters, oil collectors, buffers, scrubbers, copper wash towers, drying towers, steam towers, absorption towers, deaerators, etc.
Storage pressure vessel
Storage pressure vessel is mainly used for storage, holding gas, liquid, liquefied gas, and other media pressure vessels, such as various types of storage tanks.
Product inspection of pressure vessel
External inspection
External inspection, also known as operational inspection, the main content of the inspection are pressure vessel external surface cracks, deformation, leakage, local overheating, and other abnormal phenomena; safety accessories are complete, sensitive, and reliable; fastening bolts are intact, all tightened; foundation sinking, tilting and corrosion layer damage and other abnormalities. External inspections are usually part of the inspectors' and operators' daily tour inspection programs. Found safety-threatening phenomena (such as cracks in pressurized components, deformation, serious leakage, etc.) should be shut down and promptly reported to the relevant personnel.
Internal and external inspection
Tests for internal and external inspection of the pressure vessel must be cleaned after stopping and internal cleaning of the vessel is sufficient. In addition to the main content of the inspection, including all the external inspection, but also tests the internal and external surface corrosion and wear phenomenon; Checking all welds, head transition zones, and other stress concentration areas for cracks with the naked eye and magnifying glass, and checking the internal quality of welds with ultrasonic or radiographic flaw detection if necessary; measurement of wall thickness. If the measured wall thickness is less than the minimum wall thickness of the container, should be re-calibrated for strength, pressure reduction, or repair measures; may cause changes in the metallurgical organization of the metal material container, if necessary, should be metallurgical inspection; high pressure, an ultra-high-pressure container of the main bolts should be used to check for cracks using magnetic powder or coloring, etc. Through internal and external inspection, the defects detected should be analyzed and proposed to deal with the causes. Repairs to be re-inspected. Pressure vessel internal and external inspection cycle for every three years, but the strongly corrosive media, highly toxic media container inspection cycle should be shortened. The operation of the vessel was found to have serious defects and poor welding quality, the material of the medium corrosion resistance of unknown containers should also shorten the inspection cycle.
Comprehensive inspection
In addition to the above-mentioned inspection items, a comprehensive inspection of the pressure vessel also requires a pressure test (generally a hydrostatic test). A sampling of the main welds for non-destructive testing or all weld testing. For very low-pressure, non-flammable, or non-toxic, non-corrosive media containers, if no defects are found, after some experience, cannot be non-destructive flaw detection inspection. Comprehensive inspection cycle of the container, generally at least once every six years. Containers for air and inert gas manufacturing qualified containers, in the use of experience and one or two internal and external inspections to confirm that no corrosion, a comprehensive inspection cycle can be extended.
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