Narin, yes, hub per the Figure. Possibly both sides of both inner & outer tubesheets, depending on the service. However it seems to me that if both shell & tube sides were in the same lethal service there would be no need for double tubesheets. Also See UW-2(a)(3) & (4).
TEMA has rules applicable to double tubesheet design you may find helpful.
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand