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Storage tanks are widely used in the fluid industry for storing raw materials, finished products, and intermediate products. They play an irreplaceable role in ensuring the safe operation of facilities, promoting energy conservation and emission reduction, and improving overall management efficiency. **Strategic reserves also rely on various types of storage tanks. Industrial storage tanks are generally made of steel; materials such as carbon steel, low-temperature steel, and stainless steel are chosen based on the properties of the substance to be stored, as well as parameters such as storage temperature and pressure. Other materials like fiberglass and plastics are not considered due to issues related to fire resistance and compressive strength. Storage tanks are classified by structure into: spherical tanks, horizontal tanks, dome tanks, external floating roof tanks, and internal floating roof tanks. Spherical tanks: Spherical tanks are large-capacity, pressure-resistant spherical storage vessels that are widely used in process industries such as petroleum, chemicals, and metallurgy. They are often employed as storage containers for liquefied petroleum gas, liquefied natural gas, liquid oxygen, liquid ammonia, liquid nitrogen, and other substances. It can also be used as a storage tank for compressed gases (air, oxygen, nitrogen, city gas, etc.). Spherical tanks are used for storage at normal temperatures, low temperatures, or ultra-low temperatures. It is generally used to store materials whose saturated vapor pressure at storage temperature is greater than atmospheric pressure. At-ambient temperature spherical tanks, such as those for liquefied petroleum gas, nitrogen, gas, oxygen, etc. Such spherical tanks have high pressure, which depends on the saturated vapor pressure of the liquefied gas or the outlet pressure of the compressor. The design temperature for spherical tanks at normal temperatures is greater than -20°C. Low-temperature spherical tanks: These tanks are designed for temperatures of -20°C or lower, usually not lower than -100°C. Deep-cold spherical tanks, designed for temperatures below -100°C, are often used for storing substances at temperatures below their liquefaction point; the pressure is not high, and it is sometimes at atmospheric pressure. Due to the high requirements for heat insulation, a double-layer spherical shell is often used. Horizontal tank: Horizontal tanks have a small volume (usually less than 100 m3) but require a large amount of floor space. It is mainly used for storing chemicals such as acids and bases, and in production facilities it is also often used for storing other substances in small quantities (substances whose saturated vapor pressure at the storage temperature is greater than or equal to atmospheric pressure). The cylindrical body of a horizontal tank is parallel to the ground; saddle supports are commonly used. It is typically used for pressure storage and can withstand high positive and negative pressures, classifying it as a pressure vessel. Dome tank: A dome tank is a steel container with a spherical roof and a cylindrical body. Roofed storage tanks are simple to manufacture and inexpensive, which is why they are widely used in many industries both domestically and internationally. The most common capacity range is 1000 to 10,000 m3, while the maximum capacity of roofed storage tanks used in China has reached 30,000 m3. Vault tanks are generally low-pressure or atmospheric pressure storage tanks that are widely used in the fluid industry. They are commonly used for storing liquids of categories B and C, and can also be employed for storing liquids of categories A B and B A when special storage requirements exist. Abroad, they are also used for large-scale cryogenic storage of LNG. Arched roof tanks can sometimes also be used for large acid and alkali storage tanks. Floating roof tank: A floating roof storage tank consists of a floating roof that floats on the surface of the medium, along with vertical cylindrical tank walls. The floating roof rises and falls as the volume of the medium inside the tank increases or decreases. An annular sealing device is present between the outer edge of the floating roof and the tank wall, ensuring that the medium inside the tank is always directly covered by the inner floating roof, thereby reducing vaporization of the medium. Floating roof tanks are commonly used for storing Class A B and Class A C liquids whose saturated vapor pressure at storage temperature is below atmospheric pressure. Floating roof tanks are divided into internal floating roof tanks and external floating roof tanks. External floating roof tanks are open, cylindrical steel storage tanks commonly used to store volatile petroleum products such as crude oil, gasoline, or kerosene; unlike dome tanks without a floating roof, they do not have any space for vaporization. It not only reduces product evaporation losses but also decreases environmental pollution, lowering the risk of flammable substances mixing with air to form explosive gases. A gap of 100–500 mm exists between the tank shell and the external floating roof to prevent jamming during operation. An edge sealing system is used to reduce evaporation at the edges, and a central drainage system is installed on the floating roof to ensure that water accumulated during rainy or snowy weather can be drained properly, thereby preventing sinkage incidents. An internal floating roof tank is a floating roof tank equipped with a roof; it is also a storage tank that combines elements of an arch roof and a floating roof, with an arch roof on the outside and a floating roof on the inside. Internal floating roof tanks have unique advantages: first, compared to floating roof tanks, the presence of a fixed roof enables effective prevention of the intrusion of wind, sand, rain, snow, or dust, thus ensuring the quality of the stored liquid. At the same time, the inner floating disk floats on the liquid surface, eliminating any vapor space above the liquid and reducing evaporation losses by 85% to 96% ； It reduces air pollution and the risk of fires and explosions; even in the event of a fire, it prevents widespread burning. It also helps to maintain the quality of the stored liquid, making it particularly suitable for storing high-grade gasoline and jet fuel, as well as toxic petrochemical products ； Since there is no gas space on the liquid surface, corrosion of the tank walls and roof is reduced, thereby extending the service life of the storage tank. Secondly, under the same sealing conditions, it can further reduce evaporation losses compared to floating roofs. Compared to dome tanks, internal floating roof tanks require more steel plates and have higher construction requirements ； Maintenance is inconvenient (due to the sealing structure), and it is difficult to make storage tanks larger; currently, their capacity generally does not exceed 10,000 m3. Classification of tank areas: In the fluid industry, storage tanks are generally grouped together based on their purpose or pressure level, and such groups are referred to as tank areas. Based on the medium and pressure level, they are generally classified into atmospheric pressure tank areas, spherical tank areas, acid and alkali tank areas, and cryogenic tank areas. By purpose, they are usually divided into raw material tank areas, intermediate tank areas, and finished (produced) product tank areas. Within each tank area, further subdivisions into different tank groups are made based on the type of storage tank, the properties of the medium, pressure levels, as well as explosion-proof and fire-safety requirements. Standard specifications are adopted in the design of tank farms. The domestic standards commonly used in such designs include: SH/T3007 \"Code for Design of Tank Farms in Petrochemical Storage and Transportation Systems\", SH/T3014 \"Code for Design of Pumping Stations in Petrochemical Storage and Transportation Systems\", SH3136 \"Code for Safe Design of Spherical Storage Tanks for Liquefied Hydrocarbons\", GB/T20368 \"Production, Storage, and Transportation of Liquefied Natural Gas (LNG)\", GB50160-2008 \"Code for Fire Protection Design of Petrochemical Enterprises\", and GB50493-2009 \"Code for Design of Detection and Alarm Systems for Flammable and Toxic Gases in Petrochemical Industries\". The safe operation of tank farms and storage and transportation systems is crucial; industrial storage tanks often hold flammable, explosive, or toxic substances, so ensuring safe operations in these areas is of top priority. Appropriate measures must be taken to prevent fires, explosions, leaks, and other hazards. For flammable and toxic media, detectors shall be installed in accordance with regulatory requirements, and the alarm signals shall be transmitted to a manned on-site control room or fire duty room. The installation of on-site detectors should take into account factors such as the properties of the medium, environmental conditions, and wind direction, as well as the limitations of the detectors themselves. In addition to arranging the tank area in accordance with fire protection regulations, the fire protection requirements of the instruments themselves must also be taken into account. Flame-retardant cables are typically used, and the cables can be laid in metal trays or buried; they should be led from the top of the dike to outside it, or effective fire sealing measures should be applied. To prevent the expansion of accidents in the event of a fire, emergency shut-off valves should be installed at the inlet and outlet of tanks that store flammable materials. It is necessary to ensure that these valves remain in their safe position in the event of a power failure or gas supply failure. Emergency shut-off buttons should also be installed at the entrances and exits of the enclosures; such buttons are typically installed on a per-tank basis, meaning that in the event of a fire, all valves for entering and leaving the tanks within that enclosure will be shut off. When pneumatic valves are used, PVC or nylon tubing should be used to wrap around the valve body. Emergency shut-off valves must have a fire-resistant structure. Appropriate instruments should be installed to prevent overfilling and emptying of the storage tanks, and the consequences of instrument failure or malfunction must be taken into account. Depending on the continuity and level of risk associated with tank area operations, solutions such as two-out-of-one, two-out-of-two, or three-out-of-two systems can be employed. The instruments in the tank farm should also adopt appropriate anti-static and lightning protection measures in accordance with the specifications. For the measuring instruments such as those for liquid level, temperature, and pressure in flammable liquid storage tanks, armored cables or conduit pipes should be used for wiring; the cable insulation or the conduit pipes must be electrically connected to the tank body. Meters installed on-site must meet the environmental requirements; electronic meters installed on-site should have a protection rating of at least IP65 as specified by the IEC60529 and GB4208 standards, while non-electronic meters installed on-site should have a protection rating of at least IP55. All electronically operated instruments installed on-site shall be selected in accordance with the classification of the hazardous area, and must be products that meet the IEC60079 standard or GB3836 standard and possess an **explosion-proof certification. It is worth noting that low temperatures in the environment may increase the explosive power. The temperature range for which the explosion-proof certification specified in GB3836 applies is above -20°C; therefore, when the ambient temperature is below -20°C, appropriate measures should be taken or another type of explosion-proof design should be used. Common instruments for tank areas and storage and transportation. Storage tanks are storage devices widely used in the fluid industry; their parameters such as liquid level, temperature, density, and pressure (for tanks under pressure) are measured in order to calculate the volume and mass of the stored liquid. Additionally, these instruments are used for controlling the inlet and outlet valves as well as for measuring the flow rates at these points. The refrigeration of low-temperature storage tanks is not discussed here. Storage tanks are generally divided into two main categories: intermediate tanks and trading tanks (for raw materials and finished products). The intermediate storage tank only monitors parameters such as liquid level, temperature, and pressure (for tanks under pressure) in order to prevent accidents such as overfilling or vacuum formation in the oil tank; there is no need for volume measurement at transfer times ； The level, temperature, density, volume, and mass of the medium contained in the tanks used for trading must be monitored and measured with high precision. Oil tanks of different volumes and types require level gauges with varying performance characteristics. Therefore, it is necessary to select the appropriate level gauge based on the user’s needs and investment constraints, in order to achieve the best possible performance-to-price ratio. For instruments other than those used for measurement, the requirements for stability and reliability are higher than those for accuracy. When selecting instruments, appropriate ones should be chosen based on environmental conditions (temperature, humidity, altitude, marine climate, wind and sand, etc.), the type of storage tank, the maintenance and operation cycles of the tank farm, as well as the full life cycle cost. Sonic external level gauge – Dinghua Electronics’ sonic external level gauges are widely used in the petrochemical industry, with thousands of users having adopted them successfully. An external level gauge operates on the principle of sonar-based distance measurement; it is a device that uses \"micro-vibration analysis\" technology to measure the liquid level from outside the container. It requires no holes to be made in the tank wall, no flanges, and no need for welding or cleaning of the tank. It does not come into contact with the liquids or gases inside the tank, allowing for online installation and maintenance – making it a completely non-contact, isolated type of gauge. Advantage analysis: Technical advantages: Stable page tracking. It features patented \"micro-vibration analysis\" and \"small blind zone\" technologies that, through advanced intelligent processing methods, overcome interference factors such as the significant attenuation of sonar signals when passing through container walls and changes in the sound speed of liquids. It can identify and reject disturbances such as residual vibrations on the container walls, multiple echoes, and false echoes; its intelligent echo recognition algorithm ensures that the liquid level can always be effectively tracked and monitored. Maintain the highest level of precision at all times. When the temperature and composition of the liquid change significantly, it has a substantial impact on the speed at which sonar signals travel through the liquid, leading to measurement errors. The patented \"self-calibration\" precision technology addresses this issue by using a section of known length on the tank as a reference to determine the current speed of signal propagation; based on these calculations, real-time adjustments are made to the level measurement results, thereby eliminating the effects of changes in liquid temperature and composition on measurement accuracy. The automatic calibration function ensures high precision in the measurement of instrument levels at all times. Product advantages: 1. The isolated, contactless level measurement technology is very safe. 2. Installation and commissioning, thereby reducing construction costs and maintenance expenses. 3. More reliable and durable – the measurement probe and the main unit have no mechanical moving parts, and they are tightly sealed to isolate them from the outside environment, preventing wear or corrosion. 4. It has passed the \"Functional Safety Integrity\" level certification by the Shanghai Instrumentation and Automation System Testing Institute, obtaining a SIL3 certificate.