Issues regarding the external pressure calculation of long cylinders
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This post was last edited by 311yj on 2023-11-20 at 18:58. There is a stainless steel pipe with dimensions of φ108×4, a length of 2 meters, and a flange at each end. Vacuum it. Calculated using SW6 software as follows: This cylinder is already a prolate cylinder, with a critical length of 739.43. Question 1: What does this critical length mean? Question 2: My cylinder length has exceeded the critical length; do I need to install reinforcing rings? Question 3: Does the calculation process in the image indicate that the calculation was successful?
1. The critical length is a value calculated based on the outer diameter and finite thickness; those greater than this value correspond to oblong cylinders, while those less than it correspond to rigid short cylinders； 2. No need to install a reinforcement ring ； 3. Calculation passed – approved
The critical length determines which formula should be used for calculation
If the calculated length is less than the critical length, it is considered a short cylinder; the critical pressure value depends on the calculated length； If the calculated length is greater than the critical length, it is considered a long cylinder. The critical pressure is independent of the calculated length; in such cases, once the diameter and thickness are determined, the critical pressure remains a constant value.
If you pass, there’s no need to do the work anymore. If it does not meet the requirements, the oblong cylinder can be modified into a short cylinder by adding reinforcing structures; for example, a reinforcing structure can be added every 700 units, after which the calculation methods applicable to short cylinders can be used for verification.
1. External pressure vessels can be divided into three types based on the length of their cylinders: long cylinders, short cylinders, and rigid cylinders. Rigid cylinders generally have sufficient stiffness, so stability issues need not be considered. Generally, the distinction between long cylinders and short cylinders is indicated by the critical length LCr; for example, if the container length L is greater than LCr, it is considered a long cylinder, while L
The critical length refers to the point at which, once exceeded, the calculated thickness no longer needs to increase as the length increases; conversely, the calculated thickness increases as the length grows.