What are the principles for selecting internal floating roof tanks, external floating roof tanks, and fixed-roof tanks? Thank you

External floating roofs are mainly used in large storage tanks – those over 40 meters in height, and those in which mesh shells or vaulted roofs cannot be installed; in such cases, external floating roofs are employed. Internal floating roof tanks are primarily used for storing media with volatile properties, as well as toxic, harmful, and flammable substances. The main function of the floating roof is to prevent volatilization. Generally speaking, media of types A, B, C, and D all fall into this category. Vault tanks are used to store substances that have low volatility, are non-toxic, and are not flammable.

For details, see SHT3007 4.2 Tank Selection

1.1 Above-ground storage tanks 1.1.1 Vaulted storage tanks These types of storage tanks are widely used; they are typically employed for petrochemical products with a flash point above 60°C. They can be used to store materials at room temperature as well as those at higher temperatures (up to 200°C). 1.1.2 Floating roof tanks: The tank roof is positioned above the liquid surface of the stored medium and rises and falls with it. There is essentially no gas space between the floating roof and the liquid surface, which reduces gas evaporation losses and also lowers the degree of environmental pollution caused by gases. Due to the gap between the side of the tank top and the tank wall, a small amount of rain, snow, and wind-blown dust may seep into the tank; therefore, it is only suitable for storing lightweight liquid petroleum products (with a flash point of less than 60°C) for which the requirements regarding water and dust resistance are not very strict. This structure is more suitable for storage tanks with a volume greater than 1x10 m3. For light diesel, which requires large-volume storage tanks, when the capacity of a vaulted tank is not sufficient, a floating roof tank should be used. Due to the constraints of the sealing system design, the operating temperature of the medium generally does not exceed 70°C. 1.1.3 Internal floating roof tanks: Internal floating roof tanks are designed by adding a floating roof to an arch-shaped roof tank. In addition to reducing evaporation losses of the stored material and minimizing pollution from gases to the surrounding environment, they offer better waterproofing and dustproofing properties compared to ordinary floating roof tanks; hence they are more suitable for storing petrochemical products for which high standards regarding product quality are required. When the flash point of the material is below 60°C and the volume of the storage tank is less than 1×10m3, a storage tank with an internal floating roof structure is recommended. 1.1.4 Spherical and horizontal cylindrical storage tanks: Storage tanks of this type can be used to store liquefied petroleum gas, light gasoline, liquid ammonia, inert gases, etc., depending on the design pressure of such tanks. In addition, horizontal cylindrical storage tanks are also commonly used to store residual liquids recovered from oil and gas venting systems, chemical reagents, and as storage tanks in vacuum systems. 1.1.5 Gas Cylinders: Commonly used are wet-type gas cylinders, which are primarily employed for collecting and storing combustible gases as well as inert gases in oil and gas venting systems. 1.2 Underground storage tanks: Due to factors such as high investment costs and long construction periods, this type of storage tank is rarely used; it is only chosen in situations where there are certain special requirements from the perspective of the processing process. For example, the fuel stations used for internal use in petrochemical enterprises and those in cities typically employ underground buried storage tanks (horizontal cylindrical structures), and the transfer storage tanks used for unloading crude oil from trains are also of the underground buried type. In summary, when storing petrochemical products and other fluids in different external environments, storage tanks with varying structures and installation methods should be selected based on the specific conditions of each case. The tank selection table lists the petrochemical products and other fluids suitable for storage in above-ground steel tanks of various designs. https://bbs.hcbbs.com/thread-3276464-1-1.html