Were you going to tell us about the CA for specific fluid and a specific Vessel MOC ?
It is impossible to answer your question for ALL liquids, gasses and temperature ranges ... Others may agree ..
Your selection, for example, of a Carbon Steel pressure vessel with a 0.25 inch CA may be cheaper than OR more expensive than the same 304/316 Austenitic Stainless vessel with a 0.00 inch CA ... Increase the operating temperature by 200 degrees and it's the other way around !
... and when your boss rushes in at the last moment and tells you the client says the process stream now has 1,000 ppm of chlorides .... change the design, material selection (and the CA) again !!!
MJCronin
Sr. Process Engineer