Design of stiffness rings

The critical load to cause buckling in a ring under a uniform radial load Fc is given by the following expression 

Dr = diameter of the ring (approximately equal to the shell outside diameter). 

Combining equations 13.55 and 13.56 will give an equation from which the required dimensions of the ring can be determined  

In calculating the second moment of area of the ring some allowance is normally made for the vessel wall the use of Ir calculated for the ring alone will give an added factor of safety. 

In vacuum distillation columns, the plate-support rings will act as stiffening rings and strengthen the vessel see Example 13.2. 

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