Thread Content
Chapter 4 Classification of Pressure Vessels The \"Regulations on Safety Technical Supervision of Pressure Vessels\" issued by the Bureau of Quality and Technical Supervision (Document No. 154 issued by the Bureau, hereinafter referred to as the \"Vessel Regulations\") classifies pressure vessels into three categories based on factors such as the operating pressure of the vessels, the degree of hazard posed by the medium, the function of the vessel, its structural characteristics, the materials used, and the overall impact on the vessel’s safety performance. (1) Category I pressure vessels: Low-pressure vessels (except those specified in paragraphs (2) and (3)). (II) Class II pressure vessels (one of the following situations, except as specified in paragraph (III)): (1) Medium-pressure vessels ； (2) Low-pressure vessels (only for media with extremely high and high toxicity) ； (3) Low-pressure reaction vessels and low-pressure storage vessels (only for flammable media or media with moderate toxicity) ； (4) Low-pressure shell-and-tube waste heat boiler ； (5) Low-pressure glass-lined pressure vessels. (III) Class III pressure vessels (one of the following situations): (1) High-pressure vessels. (2) Medium-pressure vessels (only for media with extremely high and high toxicity) ； (3) Medium-pressure storage vessels (only for flammable or moderately hazardous media with pV greater than or equal to 10 MPa·m3) ； (4) Medium-pressure reaction vessel (only for flammable or moderately hazardous media with pV greater than or equal to 0.5 MPa·m3) ； (5) Low-pressure vessels (only for media with extremely high or high toxicity levels, and where pV is greater than or equal to 0.2 MPa·m3) ； (6) High-pressure and medium-pressure shell-and-tube waste heat boilers ； (7) Medium-pressure fiberglass-lined containers ； (8) 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) ； (9) Mobile pressure vessels, including railway tank cars (for liquefied gases and cryogenic liquids), tank trucks, liquefied gas transport (semi-trailers), cryogenic liquid transport (semi-trailers), permanent gas transport (semi-trailers), and tank containers (for liquefied gases and cryogenic liquids) ； (10) Spherical storage tanks (volume greater than or equal to 50 m3) ； (11) Low-temperature liquid storage containers (capacity greater than 5 m3). From the perspective of safety technology management, pressure vessels can be classified into two main categories: fixed vessels and mobile vessels. 1. Fixed containers refer to those that have a fixed location for installation and use, with relatively constant process conditions and operators; they are generally not installed separately but rather connected to other equipment through pipelines. Such as synthesis towers, steam generators, shell-and-tube waste heat boilers, heat exchangers, separators, etc. 2. Mobile containers refer to types of storage containers, such as gas cylinders, road tankers, and railway tank cars. Its main use is to transport pressurized gases. Such containers have no fixed location for use, generally lack dedicated operators, operate in constantly changing environments, are complex to manage, and are prone to accidents. Classified by their principle of operation in the production process, pressure vessels can be divided into reaction vessels, heat exchange vessels, separation vessels, and storage and transportation vessels. 1. A reaction vessel refers to a container primarily used to carry out physical and chemical reactions of a medium. Such as reactors, reaction kettles, generators, decomposition pots, decomposition towers, polymerization kettles, autoclaves, synthesis towers, shift reactors, cooking pots, steam balls, etc. 2. Heat exchange vessels refer to vessels primarily used for facilitating heat exchange of fluids. Such as shell-and-tube waste heat boilers, heat exchangers, coolers, condensers, evaporation pots, heaters, vulcanization kettles, disinfection kettles, autoclaves, cooking vessels, dyeing machines, etc. 3. A separation vessel refers to a vessel primarily used for achieving fluid pressure balance of the medium and for gas purification and separation. Such as separators, filters, oil collectors, buffers, energy storage devices, washers, absorption towers, copper washing towers, drying towers, etc. 4. Storage and transportation containers refer to containers primarily used for holding raw material gases, liquids, liquefied gases, etc., for industrial and domestic use. Such as various types of storage tanks, tank cars (railway tank cars, road tank cars). In a container, when there are two or more process principles operating simultaneously, it should be classified according to the primary function within the process. The Classification of Pressure Vessels in the Regulations: To facilitate safe technical management and supervision and inspection, the Regulations classify the vessels within their scope of application into three categories, based on factors such as the vessel’s pressure level, the hazard level of the medium contained within it, and its importance in the production process. The terms related to waste heat boilers mentioned in the above classification are defined as follows: Waste heat boiler – a device that uses waste heat such as heat from chemical reactions or exhaust gas to generate steam. Depending on the heat source, the former primarily utilizes the heat from chemical reactions, while the latter makes use of the waste heat from flue gas. The waste heat boilers in the aforementioned classification are of the shell-and-tube type; such shell-and-tube waste heat boilers are regulated in accordance with the Provisions on Safety Inspection of Pressure Vessels, while those of the flue type are regulated in accordance with the Provisions on Safety Inspection of Steam Boilers. Other classification methods: 1. Based on the wall thickness of the container, there are thin-walled containers and thick-walled containers. a. Thin-walled vessels: K = (Do/Di) ≤ 1.2; Thick-walled vessels: K = (Do/Di) > 1.2. 2. Based on the geometric shape of the shell, there are spherical vessels, cylindrical vessels, and conical vessels. 3. Based on the manufacturing method, they are divided into welded containers, forged containers, riveted containers, cast containers, and various container types manufactured through combined methods. 4. Based on the structural material, containers can be classified into steel containers, cast iron containers, non-ferrous metal containers, and non-metallic containers. 5. Based on the way in which they are installed, containers can be divided into vertical containers and horizontal containers, among others. Additionally, when classifying them according to manufacturing permission levels, the following factors are generally taken into consideration: (1) Classification by pressure, type, medium, and flammable media. A. Classified by pressure, they are divided into low, medium, high, and ultra-high pressure categories; the first three categories have similar requirements regarding materials, failure criteria, calculation methods, and manufacturing standards, whereas ultra-high pressure containers require entirely different approaches. B is classified according to the toxicity and flammability of the medium, primarily for safety reasons, that is, to determine the severity of potential hazards in the event of an accident (explosion, leakage, etc.). (2) Classification by manufacturing permission level: Under classification by manufacturing permission level, factors such as safety and the difficulty of manufacturing are generally taken into account. These include parameters such as P, P·V, medium properties, and material strength levels. The location where the equipment is installed can be fixed or mobile; higher safety requirements apply to mobile installations, and special considerations must be given to reducing weight, preventing impacts, and installing various instruments. As for materials, there are significant differences in manufacturing and inspection methods between metal and non-metal containers. Manufacturing characteristics should also be considered to facilitate specialized production, such as in the case of spherical tanks. Different resource requirements and safety and quality standards are set for enterprises at different manufacturing permission levels. “Permission Conditions”