Discuss a problem existing in a design
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In the workplace, has anyone experienced this: a device that was the subject of thorough discussions during its design and has proven to be safe in practical use, yet it is not possible to produce the required strength calculation documents. How did you solve this problem?
Apply the specified pattern. I have encountered the problem raised by the original poster. For example, when the cylinder is under external pressure, reinforcement is generally done using section steel rather than circumferential reinforcement. But without axial reinforcement of the cylinder, it seems there is no fixed pattern. Therefore, only the prescribed model can be used for design calculations.
I’ve encountered this situation before as well; after going through a great deal of information, I managed to get by, but I still felt uneasy. :L
There’s no need for a fixed format either; as long as you have your detailed calculation sheet, that’s sufficient.
Relevant foreign standards can be referred to for calculations
This problem is common in normal-pressure or external-pressure design; it usually arises because standard formulas cannot be applied or because the calculations are complicated. However, since the level of risk is low, empirical design is the best approach.
GB150 \"Steel Pressure Vessels\" 1.4 For pressure components for which the structural dimensions cannot be determined using this standard, it is permissible to use the following methods for design, provided that such methods are evaluated and approved by the National Technical Committee for Standardization of Pressure Vessels. ——Stress analysis, including the finite element method ； ——Verification experimental analysis (such as experimental stress analysis, verification hydrostatic tests) ； ——Empirical design is carried out by comparing with comparable structures that are already in use. So you can proceed with your design according to this rule
Provide all previous data on similar devices as a basis for design, and proceed in accordance with the relevant specifications
Haha, the original poster can be considered a beginner in this field – that’s something common. Many designers with decades of experience manage to develop various products, but when asked why they chose a certain type of valve, they sometimes can’t explain it clearly. Actually, there are two ways to approach this: 1. Do what others do; this works well for development purposes. 2. When it’s impossible to make accurate calculations, estimate based on the worst-case scenario or on experience
For example, I once designed an evaporator with a diameter of 3600, and the diameter of its tube sheet was 3800; clearly, this exceeded the specifications set by GB151. Calculations were not carried out according to GB151 standards, but you can’t just say that no calculations were done. Instead, the calculation was performed using the method of calculation flanges, and it can be said that factors such as the heat exchange tubes and control elements were not taken into account.
We deal with custom equipment, and we often encounter such situations; usually, we look for something similar to the standard and use analogous design methods. At the same time, it’s slightly more conservative than the standard requirements, to provide peace of mind, hehe.
When our factory used to manufacture pressure vessels, the supports were not calculated at all; many of the custom designs were chosen based on analogy or experience. During the last renewal process for the pressure vessel design approvals, experts stated that it was necessary to calculate the supports. It seems that software cannot be used for this purpose, and manual calculation is quite troublesome.
Analogous to previous designs, but more attention must be paid to safety issues, seeking change while maintaining stability.
Go by experience; as long as there is a basis for it, that’s fine