Hello,
It is unclear from your P&ID if the vessel V110 is located on the ground.
From the look of the P&ID, the vessel seem to also serve a gas/liquid seperation purpose, If such is still the case, use the maximum level of liquid normally operated in the vessel, using the sight glass indication of such maximum level.
If that is the case, the impact of the fire on this liquid need to be considered, vaporisation normally generate more capacity requirement than thermal expansion of gas.
In both case, fire case normally consider the first 25 ft of elevetion to be exposed to fire. This will mean the total surface area of the pressure vessel if the total height is less than 25 ft.
Some Client standard will exempt the area behind the skirt from exposition to fire if only 1 opening of limited dimension is present, confirm if such standard is applicable to your case before considering using this exemption as it is not the conservative approach.
Regards.
Marc-Andre
Edited by Marc-Andre Leblanc, 28 August 2014 - 03:05 PM.