Hi,
The latest edition of API STD 650 (13th) addresses vacuum design or design for external pressure in Annex V but mentions that the procedures in the Annex are limited to an external pressure of 1 psi (-1 psig). Full vacuum conditions are not addressed. API STD 620 also does not address full vacuum design. Essentially based on these two standards a full vacuum design is not available.
Only the PV code ASME Section VIII is the one that includes a full vacuum design.
So going strictly from codes and standards limits you in the design of a suitable tank for your application. However, special designs can be done with due testing and certification from the fabricator wherein the tank is certified to operate under deep vacuum conditions (full vacuum is a hypothetical value). You will have to find a fabricator who can provide such a special design and who can provide you references for a similar installed tank working satisfactorily and with due certification of the design conditions of the tank. Cost would be an unknown factor for such a design (probably quite expensive).
BTW, you can hookup your tank vent or multiple tank openings to some kind of a closed system so that you don't have to worry about environmental release during steam-out and avoid going for such a special design of full vacuum. My 2 cents.
Regards,
Ankur.