Depressuring Query

Dear all,

I am doing depressuring for the first time. I need advice for the following:

Let me give you the background of my system. It’s an LPG Mercury Adsorber. Operated at 8.0 barg and Designed for 40 barg based on the maximum shutoff pressure of upstream LPG supply pump. It’s an liquid filled system at normal operating condition with entry from top of the vessel and exit from bottom.

As per standard practice for depressuring, I have considered two cases. Fire Case for calculating maximum flow rate and Cv size and other is non-fire case for considering the minimum metal temperature.

Could you please clarify the following:

1) Do we need to consider piping liquid volume for calculation of total volume?
2) There are various options for the vapour equation for the Cv calculation. Which to select based on which condition?
3) For Non-fire case (adiabatic case) do we need to depressurize upto atmosphere or upto 50% or 7 barg whichever is lower (by manipulating the time required to depressurize)?

Do anyone have any guidelines/basis/any doc related to depressuring, please forward to me at gunjan8882@gmail.com.