This is wrt ASME S8D1 edition 2007 para UHX-14.5.9(b) which deals with checking the tubes for buckling stress in case of a floating head heat exchanger.

Can anybody explain the reasoning/logic behind this para which is relevant for floating head shell and tube heat exchangers?

As this para is valid for FLOATING head heat exchangers, I am unclear as to how compressive stresses and correspondingly how bucking stresses are induced in the tubes.

Thanks in advance to share your perspective.