It is not a common practice to provide only web plate to support the vessel, for the reason stated by "marty007" above.
Since only limited design data is available in the question, approx. check yields a thick of 2 to 3 mm, considering this thickness, if the overall weight of the equipment is...
To be more specific, during steam out the steam will be sent inside the vessel for cleaning during the maintenance as explained by Mr.Bhushan above, once steam is sent in, some portion of the steam will get condensed inside the vessel, during condensation some vacuum will form inside the vessel...
hi aiwa7777,
i hope after adding the corrosion allowance to the calculated vessel thickness, definitely you would have rounded off it to have a nearest integer or to obtain the commercially available plate thickness, then in that case you are increasing the plate thickness more than what...