Value of A in saddle calculation
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The standard for horizontal vessels specifies that the distance A from the center of the support to the tangent line of the head should be as small as possible, equal to or less than 0.5Ra, and should not exceed 0.2L. There is a question: if the end face of the cylinder is not a head but a flange, how should this value of A be determined? The head is provided with rigid support, so the value of A is determined by adding in the length of the straight sections of the head. For flanges as well, they themselves offer rigid support; therefore, should the value of A be increased by the length of the shorter end? It’s better to be cautious; what is the A value, and what does it represent – the distance to the flange sealing surface?
If the end face of the cylinder is a flange, the value of A should be the distance to the flange sealing surface. Since flanges do not possess as high surface rigidity as end caps, a more conservative approach is to determine the value of A based on the distance from the flange sealing surface. .
The value of A is chosen with the aim of balancing the effects of bending moments as much as possible; therefore, the standard uses the term \"appropriate\" from a stress perspective. As a result, it can be seen that the positions of the saddles in many drawings do not meet this requirement. This is due to layout considerations and specific needs – in short, it is acceptable as long as the calculations meet the required standards. The poster is currently in France; whether the exact position of the saddle is suitable or not, there’s no need to pay too much attention to that 0.2 value – it’s better to rely on the results of the final strength calculations instead
I’m currently using PV for the calculations. If I calculate based on the flange sealing surface, the calculation for the saddle doesn’t work; but if I calculate based on the smaller end of the flange, it works.
That means that in your saddle calculation, the local stress value of the cylinder is at the allowable limit; when the head serves to reinforce it, the stress remains within the allowable range, otherwise it exceeds the allowable stress value. Make adjustments based on the results from the calculation sheet
Yes, it’s operating at the allowable stress level; there isn’t much margin left. It’s a long story – the sending and receiving cylinders have the same inner diameter, DN150; the steel plates can’t be rolled, and the position of the saddle has also been determined.