The equipment has a constant-pressure inner cylinder and a positive-pressure jacket; how is the calculation for the inner cylinder done?
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I encountered a mixing tank of this type: the inner cylinder operates at atmospheric pressure, while the jacket is fed with 0.4 MPa steam; the lower end cap of the inner cylinder is an elliptical cap, and the upper end cap is a flat cover. Since the inner cylinder is at atmospheric pressure, the flat cover is very thin; whereas, based on the external pressure of the jacket and given the high water pressure in the inner cylinder, the flat cover would have to be thick, resulting in material waste. In this case, how is the inner cylinder calculation sheet prepared? Should it be set at 0.001?
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For the mixing tank you described, where the inner cylinder is at atmospheric pressure while the jacket is under a positive pressure of 0.4 MPa, the following points need to be considered during equipment design and calculation: 1. **Inner cylinder pressure**: Since the inner cylinder is at atmospheric pressure, its internal pressure can theoretically be considered as 0 MPa. However, in practical design, a small safety factor or operating pressure (such as 0.05 MPa or lower) is usually considered for strength calculations to ensure the safety of the container. 2. **Basis for calculation**: In accordance with China’s relevant pressure vessel standards (such as GB 150.1-2011), the inner cylinder, being a vessel under normal pressure, can be designed and calculated in accordance with the specifications for vessels under normal pressure. Even when the inner cylinder is subjected to external pressure from the jacket, the focus is primarily on the structure’s resistance to that external pressure. 3. **External pressure effect**: Since the steam in the jacket may exert a certain external pressure on the inner cylinder, it is necessary to perform calculations regarding the external pressure resistance of the inner cylinder’s structure (especially the flat cover section), to ensure that excessive external pressure does not cause deformation or damage to the inner cylinder. 4. **Flat cover design**: For the flat cover on the upper head, since it is used under atmospheric pressure and is subjected to external pressure, its design thickness cannot be determined based solely on internal pressure; rather, the minimum thickness required to withstand external pressure must also be taken into account. If only the calculation method for normal-pressure containers is used here (for example, by using 0.001 MPa), it may result in a lid that is too thin to meet the safety requirements under actual operating conditions. In summary, the calculation of the inner cylinder should be carried out as for a pressure vessel at normal pressure, taking into account both the internal pressure and the effect of external pressure to ensure design safety. It is recommended to consult experienced pressure vessel design engineers in detail or refer to relevant design standards in order to carry out more accurate pressure vessel design and calculations. .
Alternatively, calculating with a flat cover reinforcement is also an option; it depends on the diameter of the equipment
Does the external pressure of the jacket cover the flat lid? The jacket usually only covers the lower head and the cylinder body of the inner tube; since there is no jacket on the upper flat cover, external pressure need not be considered.
This post was last edited by wanlirn on 2024-7-24 at 10:56. You have mixed up design pressure and calculated pressure; the inner cylinder is at atmospheric pressure, while the jacket is at positive pressure. The calculated pressure used for determining the internal pressure of the inner cylinder is based on the pressure in the jacket； The jacket hydrotest pressure is used as the calculated pressure for external pressure verification.
The design pressure of the inner cylinder definitely can’t be reduced; flange covers are essential, so costs can’t be cut that much
As mentioned on floor 7, if the flat cover is not covered by a jacket (generally, the jacket of a reaction vessel covers only the inner cylinder body and the lower head), then the flat cover is considered to be under normal pressure. However, when calculating the thickness of the flat cover, it is necessary to take into account the loads it must withstand, such as the weight of the mixing system, snow loads, as well as the required stiffness.