What should the Blowdown valve (BDV) status be after depressuring ? After reaching the isolated vessel pressure of 50% of design pressure or 100 psi (according to API Std 521), should the BDV be closed or keep in open position ? If in open position, the vessel pressure will be equalized with the flare system pressure. Any associated problem ?
BDV would be in open position (Fail safe position) to ensure evacuation of Hydrocarbon inventory…
To equalize the vessel pressure with the flare system pressure would take very long. Normally, an operator would take action to initiate the closure of the BDV for last few bar.