Pressure vessel, generally refers to the industrial production used to complete the reaction, mass transfer, heat transfer, separation and storage and other production processes, and can withstand the pressure of airtight containers. It is widely used in petroleum, chemical, energy, metallurgy, machinery, textile, medicine, defense and other industrial fields. First, the basic knowledge of pressure vessels 1 pressure vessel operating conditions (1) pressure. Pressure vessel pressure can come from two aspects, one from outside the pressure vessel, one from within the pressure vessel. The maximum working pressure of the pressure vessel, the pressure vessel under internal pressure, refers to the pressure vessel during normal use, the maximum pressure may occur at the top of the container; for external pressure to withstand pressure vessels, refers to the pressure vessel during normal use , The maximum pressure that may appear on the top of the jacket. The design pressure of a pressure vessel means the pressure used to determine the thickness of the vessel shell at the corresponding design temperature, ie the design pressure of the vessel marked on the nameplate, which shall not be less than the maximum working pressure. When all parts of the container or pressure components to withstand the liquid column static pressure reaches 5% of the design pressure, then the design pressure and liquid column should be static pressure and the design of the parts or components should be calculated; with safety relief device Pressure vessels, the design pressure shall not be lower than the safety relief device opening pressure or burst pressure. The design pressure of the container shall be determined according to the corresponding provisions of GB 150. (2) temperature. Metal temperature refers to the average temperature of the container pressure element along the cross-sectional thickness. In any case, the surface temperature of the component metal shall not exceed the allowable temperature of the steel. The design temperature refers to the temperature of the metal of the pressure element set under the corresponding design pressure of the container under normal operating conditions and its value should not be lower than the highest metal temperature that the element metal may reach; for the metal temperature below 0 ° C, The design temperature must not exceed the lowest metal temperature that the component metal may reach. The design temperature of the vessel (ie, the design medium temperature marked on the nameplate of the vessel) refers to the design temperature of the shell. (3) media. Production process involved in a wide variety of media, there are a variety of classification methods. According to the classification of the material state, there are gases, liquids, liquefied gases, simple substances and mixtures, etc. According to the chemical characteristics, there are four kinds of flammable, flammable, inert and combustion-supporting; I), high risk (Ⅱ), moderate harm (Ⅲ), mild harm (Ⅳ) four. Flammable medium: refers to the air mixed with the lower explosive limit of less than 10%, or the difference between the upper limit and the lower limit of explosion greater than or equal to 20% of the gas, such as monomethylamine, ethane, ethylene and so on. Toxic media: "pressure vessel safety technology supervision regulations" (hereinafter referred to as "compliance") for the degree of division of the medium with reference to GB 5044 "Occupational exposure to toxic hazard classification" is divided into four levels. The maximum allowable concentrations were: extreme harm (I level) <0.1mg / m3; highly hazardous (Ⅱ level) 0.1 ~ <1.0mg / m3; moderate harm (Ⅲ level) 1.0 ~ <10mg / m3 ; Mild hazard (Ⅳ grade) ≥ 10mg / m3. When the medium in pressure vessel is a mixture of substances, the degree of toxicity of the medium or the degree of toxicity of the medium shall be decided by the composition of the medium and according to the degree of toxicity or the principle of division of flammable medium, or whether the medium is toxic medium. Corrosive media: Petrochemical media pressure vessel material with corrosion resistance requirements. Sometimes due to impurities in the medium, the corrosion increases dramatically. Corrosive media of different types and properties, coupled with different process conditions, the corrosive media is not the same. This requires the selection of pressure vessel material, in addition to meet the mechanical properties under the conditions of use requirements, but also have sufficient corrosion resistance, if necessary, take some anti-corrosion measures. 2 pressure vessel classification. There are many ways to classify pressure vessels. In order to facilitate the monitoring and management of safety technologies, Yung Regulations classifies pressure vessels into three categories. (1) A third type of pressure vessel is one of the following: high pressure vessels; medium pressure vessels (extreme and highly hazardous media only); medium pressure storage vessels (flammable or toxic to moderately hazardous agents only , And pV is greater than or equal to 10MPa · m3); medium pressure reaction vessel (only flammable or toxic medium degree of hazard medium, and pV greater than or equal to O.5MPa · m3); low pressure vessel (toxicity only extreme and high Hazardous medium, and pV greater than or equal to O.2MPa · m3); high pressure, medium pressure shell and tube waste heat boiler; medium pressure glass-lined pressure vessel; the use of high strength level (referring to the corresponding standard tensile strength lower limit of greater than or equal to 540MPa); Mobile pressure vessels, including rail tankers (liquefied gases and cryogenic liquids), tank cars [liquefied gas transportation (semi-trailer) vehicles, cryogenic liquid transportation (semitrailers), permanent Gas transport (semitrailer)] and tank containers (medium for the liquefied gas, cryogenic liquid); spherical tank (volume greater than or equal to 50m3); cryogenic liquid storage container (volume greater than 5m3). (2) One of the following types of pressure vessels is: Medium pressure vessels; Low pressure vessels (Extremely toxic and highly hazardous media only); Low pressure reaction vessels and low pressure storage vessels (Flammable or flammable Degree of hazardous media); low pressure shell and tube waste heat boiler; low pressure glass-lined pressure vessel. (3) Low-pressure vessel is the first type of pressure vessel. Second, the safety Annex 1. Safety valve Safety valve is a kind of automatic pressure relief valve opened by the import of static pressure. It discharges a certain amount of fluid by the pressure of the medium itself to prevent the pressure in the container or system from exceeding the predetermined safety value. When the pressure in the container resumes normal, the valve closes itself and prevents the medium from being discharged. Safety valve points all-safety valve and micro-Kai safety valve. According to the overall structure of the safety valve and loading can be divided into static weight, lever type, spring type and pilot type 4 kinds. 2. Bursting disc bursting disc device is a non-reclosing pressure relief device, by the import of static pressure bursting disc rupture and venting out of the media to prevent the pressure inside the container or system exceeds the predetermined safety value. Bursting disc, also known as burst film or explosion-proof film, is a fracture-type safety relief device. Compared with the safety valve, it has a simple structure, pressure relief reaction, sealing performance, adaptability and so on. 3. Combination of safety valve and rupture disc device When the safety valve and rupture disc device are combined in parallel, the bursting pressure of bursting disc shall not exceed the design pressure of the container. Safety valve opening pressure should be slightly lower than the bursting disc calibration burst pressure. When the rupture disc device is installed in series between the inlet of the safety valve and the container, the following conditions shall be met: the discharge capacity of the combination of the safety valve and the rupture disc device shall meet the requirements; the discharge area after rupture of the rupture disc shall not be less than the inlet area of ​​the safety valve , At the same time, it shall be ensured that the fragments which rupture the rupture disk do not affect the normal operation of the safety valve; the pressure gauge, cock, vent or alarm indicator shall be installed between the rupture disc device and the safety valve to check whether the rupture disk is broken or infiltrated leak. When the rupture disc device is installed in series on the outlet side of the safety valve, the following conditions shall be met: the medium in the container shall be clean and free of adhesive substances or obstructive substances; the relief valve of the safety valve shall meet the requirements; when the safety valve and bursting disc The valve can still be opened accurately under the cracking pressure; the discharge area of ​​the rupture disc should not be smaller than the inlet area of ​​the safety valve; the vent pipe or sewage pipe should be set between the safety valve and the rupture disc device to prevent The pressure in this space is accumulated. 4. Explosion cap Explosion cap is closed at one end, with a weak section in the middle thick-walled short tube, burst pressure error smaller, smaller discharge area, more for ultra-high pressure vessel. Overpressure when the tensile stress on its weak surface reaches the material strength limit fracture. Because of their work usually have temperature effects, therefore, are generally selected heat treatment performance is stable, and with small changes in temperature of high strength steel materials (such as 34crNi3Mo, etc.), the explosion pressure and the material strength ratio is generally O. 2 ~ 0.5. 5. Fusible plug Fusible plug is a "melted" ("temperature type") safety relief device, its action depends on the temperature of the container wall, mainly for medium and low pressure small pressure vessels, in the liquefied gas Cylinder is more widely used. 6. Emergency shut-off valve, pressure relief valve Emergency shut-off valve is a special structure and special purpose valve, which is usually mounted in series with the shut-off valve on the media outlet pipe close to the container in order to emergency stop Leakage; generally also has over-current shutdown and over-temperature shutdown performance, and can operate independently in the short-range and long-range. Emergency shut-off valve according to the different operating modes, can be divided into mechanical (or manual) traction, hydraulic control, pneumatic control and electric control and other types of the first two currently used in liquefied petroleum gas tank car is very extensive . Pressure reducing valve is the use of diaphragm, spring, piston and other sensitive components to change the valve flap and the gap between the seat, when the medium through the throttle, the pressure drop to make it decompression valve. When the adjustment screw tightened down, the spring is compressed, the diaphragm pushed down, open the pulse valve flap, part of the high pressure side of the medium through the high pressure channel into the gap between the pulse valve flap and the valve into the gap Annular channel into the cylinder, pushing down the piston and open the main valve flap, then the high-pressure side of the medium valve from the main valve seat and valve seat through the gap between the throttle and decompression. At the same time, part of the low-pressure side of the medium through the low-pressure channel into the space below the diaphragm, when the pressure due to high-pressure side of the medium pressure increases and is sufficient to offset the elastic spring, the diaphragm upward push the pulse valve flap gradually closed Reduce the medium into the cylinder, the piston and the main valve flap move up, the main valve is closed, so as to reduce the amount of medium flow to the low pressure side, so that the low pressure side of the pressure will not rise due to high pressure side to achieve automatic pressure adjustment the goal of. 7. Pressure gauge, thermometer, level gauge (1) pressure gauge. Pressure gauge is to indicate the media pressure container, is an important safety device pressure vessel. According to its structure and principle of action, pressure gauges can be divided into liquid column, flexible components, piston and power four categories. Piston pressure gauge is usually used as a calibration standard instruments, hydraulic column pressure gauge is generally only used to measure very low pressure, pressure vessels are widely used in various types of elastic component type pressure gauge. (2) level gauge. Level gauge, also known as liquid level gauge, is used to observe and measure the level of container liquid level changes in the instrument. Especially for containers containing liquefied gases, the level gauge is an essential safety device. (3) Thermometer. Thermometer is used to measure the degree of hot and cold substances can be used to measure the temperature of the pressure vessel medium, for the need to control the wall temperature of the container, you must also install a thermometer to test the wall temperature. This article Keywords: safety valve
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