Application scenarios of spherical storage tanks

Spherical tanks can withstand greater pressure than other types of storage tanks, as the substances stored in them are often high-pressure and toxic.

It is also widely used in low-temperature environments, perhaps due to the convenience it offers in terms of heat retention and material savings.

Spherical storage tanks are one of the common pressure vessels used for storing various gases and liquefied gases, and they are widely employed in industries such as petroleum, chemicals, metallurgy, and urban gas supply

The key is the high pressure; spheres distribute forces well.

A comparison of the wall thickness calculations for spherical tanks and cylinders reveals the advantages of spherical tanks. At the same pressure, diameter, and material, the thickness of a spherical tank is only (approximately) half that of a cylinder.

Source: Internet. Spherical tanks are large-capacity, pressure-resistant spherical storage vessels that are widely used in industries such as petroleum, chemicals, and metallurgy. They can be used 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). 　　Compared to vertical cylindrical storage tanks, spherical tanks have the smallest surface area at the same volume and pressure, thus requiring less steel ； At the same diameter, the internal stress in a spherical tank is minimal and uniform; its load-bearing capacity is twice that of a cylindrical vessel. Therefore, the wall thickness of a spherical tank needs to be only half that of the wall thickness of a corresponding cylindrical vessel. 　　Based on the above characteristics, the use of spherical tanks can significantly reduce steel consumption, typically saving 30% to 45% of the steel needed ； Furthermore, spherical tanks occupy less space and require less foundation work, thus saving land area. 　　(1) Structure and Classification of Spherical Vessels 1. Structure of Spherical Vessels A spherical vessel consists of the main body, struts (supports), and accessories. 　　(1) Sphere tank body The sphere tank body is the main component of the sphere tank structure; it is the element that enables the tank to store materials and withstand the working pressure of those materials as well as the hydrostatic pressure. Due to the different diameters of the spherical shell, the number of shell plates also varies. Spherical shells come in three structural forms: annular type (orange segment type), football-segment type, and mixed type. 　　(2) Spherical tank supports The spherical tank supports are structural elements used to bear the weight of the spherical tank itself as well as the weight of the materials stored within it. There are various types of such supports, including column-type, skirt-type semi-submerged types, and elevated types. 　　1) Column-type bearing. The equatorial tangent column support is the most commonly used type; in addition, there are V-shaped supports or combined three-column supports. 　　2) Skirt-type support. This structure is characterized by low supports made of steel plates; its advantages are good stability and reduced steel usage. 　　3) Semi-embedded support. This structure features a hemispherical shape supported on a reinforced concrete foundation. 　　(3) Accessories of the spherical tank 1) Ladder platform. Typically, spherical tanks are equipped with a top platform and an intermediate platform, the top platform serving as the process operation platform. 　　2) Manholes and connections. Manholes are provided for operators to enter and exit the spherical tank for inspection and maintenance; they are also used during on-site assembly and welding of spherical tanks for post-welding heat treatment, as well as for air intake, combustion ports, and exhaust of smoke. 　　3) Water spray device. Water spray systems are installed on spherical tanks to provide insulation for the liquefied petroleum gas, flammable gases, and toxic gases stored there, and they also serve a fire protection purpose. 　　4) Insulation and cooling facilities. Insulation and heat retention are generally used to maintain a certain temperature of the stored medium. Spherical tanks and supports used for storing liquefied petroleum gas, flammable gases, liquefied gases, and toxic gases should be equipped with insulation facilities. When storage tanks are used to hold low-temperature materials such as ethylene and liquid ammonia, insulation devices should be installed. 　　5) Level gauge. To monitor the liquid level inside spherical tanks, a level gauge is generally installed in tanks used for storing liquids and liquefied gases. 　　6) Pressure gauge. A pressure gauge is installed to measure the pressure inside the spherical tank. Considering situations such as pressure gauges failing for some reason or being removed for inspection, a pressure gauge should be installed at both the upper and lower parts of the sphere. 　　2. Classification of spherical tanks The structure of spherical tanks is diverse; different structural forms exist depending on various operating conditions (medium, capacity, pressure, and humidity). They are usually classified according to differences in appearance shape, housing structure, and support method. 　　(1) Classified by shape into spherical and elliptical types. (2) Classified by the number of shell layers into single-layer shells and double-layer shells. 1) Single-layer shells are the most common and are used in spherical tanks operating under normal temperature and high pressure, as well as high temperature and medium pressure conditions. 　　2) Double-shell spherical tanks, consisting of an outer sphere and an inner sphere, have excellent thermal insulation properties due to the high-quality insulating material placed between the two shells, allowing them to store liquefied gases at low temperatures. Double-shell spherical tanks are manufactured using bimetallic composite sheets, and they are suitable for storing ultra-high pressure gases or liquefied gases; however, they are not widely used at present. 　　(3) Based on the combination pattern of the spherical shell, they are classified into pure orange-petal type, pure football-petal type, and football-orange petal mixed type. 　　1) The pure orange segment-style shell is formed by dividing and combining elements in an orange segment structure (also known as watermelon rind segments); this structure is referred to as the pure orange segment shell. The characteristic of this spherical shell is that its assembly welds are relatively regular, making construction simple. The pure orange-petal type shell structure has equatorial zones, and the supports for such spherical tanks are mostly in the form of equatorial tangent columns. 2) Football-petal type shell. Its advantage is that the sizes of the spherical lobes are the same or similar, making the production of splits simple and saving material. The downside is that assembly is relatively difficult, as some of the struts rest on the welds of the spherical shell, resulting in complex welding stresses in those areas. 　　3) Football orange-petal mixed shell. Its structural feature is that the equatorial band adopts an orange segment design, while the upper and lower polar plates use a football segment design. The advantages are less work required for manufacturing the sphere shell, shorter welds, and faster construction progress; it also avoids the drawbacks associated with supports resting on the sphere shell’s welds. The disadvantages are that assembling and aligning the two dome segments is complicated, and high standards are required for the manufacture of the sphere shell. 　　(4) Classified by the supporting structure, they include column-type supports and skirt-type supports, as well as semi-buried supports and elevated supports.