I have the feelint that liquid volume (and consequently its weight) is computed considering the same internal diameter, regardless that the vessel is lined or not.
Could you please confirm this?

The difference in the final operating weight can be considerable: for example, I'm just analysing a dia=4 m vessel with 230mm of antiacid lining.
PvElite is computing the liquid volume without considering the reduced diameter 4-2*0.23, so the operating weight is definitely higher then the expected.

Best regards
Federico