What to do if the pressure in the spherical tank exceeds 6.4 MPa and the diameter exceeds 50 mm?

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According to standard GB12337, the value shall not exceed 6.4 MPa for spherical tanks supported by columns； The thickness should not exceed 50 mm. How small can the volume of a spherical tank be? 【Original】Rules for determining the thickness of spherical tanks and their practical application: What are the maximum thicknesses that have been used in actual projects? As the editor understands it, the maximum thickness achieved in previous years was 54/56 mm (Q370R\15MnNbR); Jingmen Hongtu has reached a maximum thickness of 57 mm (Q370R). The Luoyang Institute has designed ethylene spheres made of 66mm (09MnNiDR) material; these are likely the thickest spheres ever built to date. If the thickness is large, then the requirements for the press are also very high. Currently, the largest press in China has a capacity of 3,000 tons; it is estimated that it can handle a maximum pressing thickness of around 100 mm without any major issues. Minimum thickness requirement: The minimum thickness of the spherical tank shell plates is not specified by standards, unlike the maximum thickness ； For the minimum thickness, as long as it meets the stiffness and transportation requirements of the spherical shell, it is generally acceptable. However, based on years of design experience, if the steel plate is too thin, the design institute usually considers increasing its thickness. The lower limit of the shell plate wall thickness is primarily determined by the stiffness requirements of the shell. During the sheet pressing process, deformation, bulging, and wrinkling can occur easily; sometimes repeated pressing and reshaping are required to achieve good pressing accuracy. Shell plates are also prone to deformation during transportation, storage, and lifting. Generally, when the plate is thinner, the design institute will divide it into more sections and install more shell plates. In actual engineering projects, what are the smallest thicknesses that have been used? It is understood that for spherical tanks with a volume of 2,000 cubic meters or less, the minimum wall thickness has been as low as 14–18 mm. For spherical tanks with a volume of 3000 cubic meters or more, the minimum thickness is above 22 mm, and the shell plates are arranged in more zones. Conclusion: Spherical tanks are generally used in medium and low pressure applications, that is, at pressures not exceeding 10 MPa; theoretically, they can be manufactured as such. However, when the pressure exceeds 7.5 MPa, it may be necessary to evaluate the cost-effectiveness of using spherical tanks. The design pressure for spherical tanks is, in principle, not more than 6.4 MPa; however, if it exceeds 6.4 MPa, special approval can be obtained through a separate review process, though this method may take a longer time. There is another approach as follows. For containers with a pressure exceeding 6.4 MPa, they can be designed in accordance with the standards GB150 and JB4732. GB150 applies to pressure vessels whose design pressure is not greater than 35 MPa; it does not specify any requirements regarding the thickness of such vessels. As long as the factory’s manufacturing capabilities and the steel rolling capabilities permit it, it is feasible to use these standards for such designs. GB150 and 4732 are general design requirements for pressure vessels; spherical tanks, being pressure vessels as well, must also comply with these two standards ； In addition, the fixed volume gauge standard is also one of the reference standards. There is no requirement as to whether a cylindrical shape or a spherical shape should be chosen. So, from now on please stop asking whether spherical tanks can still be used when the pressure exceeds 6.4 MPa; just call them spherical containers and use a different standard – they can still be used. Note that spherical tanks are a type of spherical vessel, but pressure vessels in a spherical shape are not necessarily spherical tanks.