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Jacketed vessels are typical two-chamber pressure vessels; GB/T 150.1 4.3.3 specifies that \"when determining the design pressure or calculated pressure, the design pressure for each pressure chamber shall be determined separately, and when determining the calculated pressure for common components, the maximum pressure difference between adjacent chambers shall be taken into account.\" It can be understood as follows: 1. The design pressure of the inner cylinder is determined based on the operating pressure of the inner cylinder, while the design pressure of the jacket is determined based on the operating pressure of the jacket. 2. The calculated pressure for the jacket cylinder is usually the design pressure of the jacket cavity; however, when the hydrostatic pressure exerted by the liquid column on the jacket cylinder is greater than or equal to 5% of the design pressure of the jacket cavity, this hydrostatic pressure must also be taken into consideration. 3. The inner cylinder surrounded by the jacket (the pressure-bearing element in the middle) is subjected to pressures from both sides; the calculated pressure for this section depends on the design pressures on those two sides. It should be determined based on the most severe combination of operating or non-operating conditions that may occur in the two chambers, including hydraulic testing. The design pressure parameters for the intermediate pressure element are selected based on the following different operating conditions: 1. The inner cylinder is at normal pressure while the jacket is at positive pressure; the wall thickness of the intermediate pressure element is determined as if it were a vessel under normal pressure conditions ； The calculated pressure using the jacket design pressure as the external pressure ； The jacket hydrostatic test pressure shall be used as the calculated pressure for external pressure verification, and the calculation results shall meet the requirements in each case. Under these operating conditions, if the external pressure check fails, priority should be given to installing reinforcing rings around the inner cylinder to prevent it from becoming unstable. 2. The inner cylinder is under positive pressure, and the jacket is also under positive pressure; if it is not possible to ensure that both sides are under pressure at all times, the design pressure of the inner cylinder shall be used as the calculation pressure to determine the wall thickness ； The calculated pressure is determined based on the jacket design pressure as the external pressure ； The jacket hydrostatic test pressure shall be used as the calculated pressure for external pressure verification, and the calculation results shall meet the requirements in each case. Under these operating conditions, if the external pressure test fails, priority should be given to installing reinforcement rings on the inner cylinder, or maintaining pressure in the inner cylinder during the jacket pressure testing. If it can be ensured that both sides are under pressure simultaneously under any operating conditions, the design pressure difference shall be used to calculate the pressure for the intermediate pressure-bearing elements and to determine the wall thickness; when the pressure inside the inner cylinder is higher than that in the jacket, the calculation shall be based on the internal pressure ； When the pressure inside the inner cylinder is lower than the pressure in the jacket, calculate based on the external pressure ； The jacket hydrostatic test pressure shall be used as the calculation pressure for checking the external pressure on the intermediate pressure-bearing components, and the calculation results shall meet the requirements in each case. Under these operating conditions, if the external pressure test fails, priority should be given to installing reinforcement rings on the inner cylinder, or maintaining pressure in the inner cylinder during the jacket pressure testing. 3. The inner cylinder is under vacuum, while the jacket is at positive pressure; the design pressure difference is used as the calculation pressure for the intermediate pressure-bearing element to determine the wall thickness ； The jacket hydrotest pressure is used as the calculated pressure for external pressure verification; if this test is not successful, measures such as installing reinforcement rings or maintaining pressure in the inner cylinder during the jacket testing can be taken. 4. The inner cylinder is at atmospheric pressure, and the jacket is under vacuum; the wall thickness is determined as for a vessel at atmospheric pressure ； The calculated pressure using the design pressure difference as the internal pressure ； The jacket hydrotest pressure is used as the calculated pressure for external pressure verification; if this test fails, measures such as installing reinforcing rings or maintaining pressure in the inner cylinder during jacket testing can be taken. It should be noted that the calculated pressure for the element under compression in the middle is, numerically, neither the design pressure of the inner cylinder nor that of the jacket; rather, it is determined by selecting the most severe combination of the pressure conditions on both sides. The above content is excerpted for reference from GB/T150 and the book \"Design of Chemical Pressure Vessels – Methods, Problems and\" written by Teacher Wang Fei