Regarding the selection of saddles for horizontal containers
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Saddles are classified into Type A (light) and Type B (heavy). Category B is further divided into five types. JB 4712.1 \"Saddle Supports\" states that it is necessary to determine whether to use a light or heavy saddle support based on the actual loading capacity of the saddle. It also specifies that the choice between a saddle support with a 120° cover angle or one with a 150° cover angle should be made according to the strength requirements of the container’s cylinder. The instructions are rather vague, and it’s not clear exactly how to make this selection
The choice between light and heavy types is determined by whether the allowable load specified in the saddle standards is applicable. The saddle wrap angle is determined by the stress at the saddle wrap angle during the design calculations of the container.
Generally, the saddle is selected based on the engineering diameter of the cylinder and the load it must bear; the wrap angle is determined primarily from a stress perspective
Are there any more specific ones? For example, what nominal diameter determines the choice of A?
They’re all specified in the saddle standards, on pages 5/6
Either AB is acceptable, but it must be calculated. The selection of saddles differs from that of equipment flanges; equipment flanges can be selected according to standards and thus do not require calculation, but saddles must always be calculated (except for heat exchangers). Although the maximum allowable load value is specified in the saddle standards, this applies only to the saddle itself. The position of the saddle, the wrap angle, as well as the size and thickness of the shims are all directly related to the stresses experienced by the equipment housing. Study NB/T47042 and its standard interpretations carefully, and it is recommended to read Brunel’s book \"Design of Pressure Vessels\".
That book is a bit old, but its content is still very useful. Thank you for the recommendation and sharing
What if the nominal diameter exceeds the specified range?
This answer is truly patient and very instructive; thank you!
Just saw it, so I’m replying: 1. When the user has no specific requirements, choose type A first. 2. Read the load value specified in the standards, and compare it with the weight of the equipment when filled with water or its operating weight (whichever is higher) plus any external loads (such as platforms or auxiliary equipment). If the value is appropriate, proceed; otherwise, choose type B instead. 3. Calculation... The most common issue here is that, due to the thin wall thickness of low-pressure equipment, it is very likely that the shear stress in the cylinder at the gasket area will not be sufficient. 4. If the shear stress is not acceptable, then change the wrap angle to 150°, add reinforcing rings, or adjust the position of the saddle. 5. If the shear stress cannot be reduced no matter what, then don’t hesitate – thicken the cylinder; even in this case, changing it to type B will not solve the problem.