I haave not handled large tanks. Max. storage capacity handled was 50 MT. We had carbon steel tanks with epoxy inner lining and silica gel as absorbent in the vent. As far as I know we did not face any problems for three years.
Does this help you

Commonly used adsorbents are: Molecular Sieves, Silica Gel, Activated Alumina, etc.  Keeping moisture out of the concentrated sulphuric acid keeps it's corrosiity down (the higher the % acid, lower the % water, the less corrosive).  A mild steel tank and piping (if velocity not too high) can handle conc H2SO4 (98% if I recall correctly).  Corrosion tables in Pery's handbook bear this out, if I recall correctly.  Of course, you have to change out the dessicant when it gets saturated; colour indicating dyed dessicants help here (colour change indicates saturation with moisture and need to replace it).
Adsorbent suppliers could help you specify dessicant for a vent; details may depend upon your local atmosphere (temperature, relative humidity).
Good luck.

Have stored conc H2SO4 in CS tanks for 25 years - no problem except when we had Silica gel absorbers in the original vents!! They HAVE to be maintained on a rigorous schedule otherwise they block the vent. We went to polypropylene vent piping and no Silica gel -no problems! Still inspect the vents annually in case something blocks them, we found no obstructions over the last 15 years and the tank internal inspections found no metal loss. Have a look at the corrosion rates in any std book and they do not get significant until in the lower 80%'s. You never get into that region with normal operation. A word of caution when reading the corrosion rates - corrosion in H2SO4 is extremely velocity sensitive, hence the suitability of CS for tanks. Keep an eye on the tank floor where the liquid hits it when filling. A bit more than your request but hope that this helps.

Thanks a lot, folks. You all have been great help. I was under the notion that when large quantities of Conc. Sulphuric acid is stored in unlined mild steel storage tanks, absorption of moisture from a highly humid atmosphere (through the vent) might pose problems due to dilution and corrosion. From the replies, it appears that these problems do not arise.
Thanks again

Deelta16,

No, you should be concerned about generation of dilute acid from improper venting....

Corrosion can and will occur if a dilute surface layer of sulfuric acid forms within a carbon steel tank.

See page 12 of:

www.genchemcorp.com/pdf/tsr5078.pdf

GENCHEM has a long history of handling H2SO4


MJC