Calculation of flanges for non-standard long-neck equipment
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Why is a minimum thickness for the butt joint of the cylinder specified in the equipment flange standard NB/T47023? For example, a DN300, PN4.0 flange with a thickness of 16 at the smaller end and a minimum thickness of 8 for the butt joint section – it is clearly not designed for welding. So where does this minimum thickness come from? When the temperature and corrosion margin exceed the standards, for the flanges of the calculation equipment, the thickness at the smaller end can be calculated based on the thickness of the smaller end of the cylinder. But some people don’t calculate it this way; they consider only the flange, and since the thickness at the smaller end is greater than that of the cylinder body, the thickness of the flange decreases. However, the calculation is done solely for the flange itself, and it seems that the issue related to the cylinder body isn’t taken into account. I don’t know how everyone calculates it. Since the temperature at this point already exceeds the standard, without performing calculations, is it correct to select the minimum thickness for the butt joint cylinder according to the standard?
How should the minimum thickness be determined? For example, the flange for equipment with DN500 and PN4.0 specifications, in accordance with NB/T47023 standards, has a larger end diameter of 26 and a smaller end diameter of 16. Connecting cylinder 10, corrosion margin 3, temperature 220. When the temperature is outside the standard range, it is calculated as a non-standard case. There are two methods: one is to use standard flanges, with a diameter of 23 at the larger end and 13 at the smaller end, and then increase the total height; after the calculation is completed, standard flanges are used again. Another case is big-endian 23 and little-endian 7, and the calculation also works. The small end diameter of the flange produced at this time is 10; 7 is the result after corrosion. The slopes of the two are the same; it’s just that the cross-sections used in the calculations are different. The latter is thicker than the former due to its smaller thickness at the minor end. My question is, according to the WATERS method, where should this little-end thickness be chosen?
According to the Waters method, the axial bending stress induced by the flange moment has essentially been reduced to zero in the conical neck section. Therefore, in flange design, the thickness of the smaller end should be the thickness at the end of the taper neck slope, independent of the straight edge section. The standard specifies a minimum thickness for the shell in order to prevent designers from arbitrarily trimming the flange’s straight edges within the limits defined by the standard; such trimming could lead to the edges reaching the smaller end of the flange, thereby causing excessive stress on it.
Could you please take a look at my post? As you said, is the input of the images and calculation sheets correct? https://bbs.hcbbs.com/thread-2365240-1-1.html