3 replies to this topic

[Priolo]

Hi,

I'm a process engineer working for the design of a unit processing LPG. The unit includes columns, heat exchangers pumps etc.
In P&ID under development I noticed that several LOCAL drain and vent, with simple valve and cap, have been added for example between control valve isolation valves, heat exchangers isolation valves etc. Being LPG a flammable and hazardous fluid is this correct? One should not connect all vent and drain to flare/closed drain system? Is it acceptable to have local drain and vent when processing hazardous fluid?

Thanks for your help

Edited by Priolo, 14 February 2026 - 02:03 PM.

[Pilesar]

Local vents and drains are common for light gas processes. Vents and drains to flare/closed drain system is expensive and has its own safety issues which require layers of additional controls. Local valve with cap is completely safe when closed. Between isolation valves, the piping volume may be small enough not to be much concern when venting. It is likely that your local vents and drains are not used routinely but are needed for maintenance purposes for purging and sweeping to enable breaking containment. 

[Priolo]

Hi,

Thank you Pelisar.
Is not a risk to depressurize LPG to atmosphere even if a small volume?

[latexman]

Hi,
Thank you Pelisar.
Is not a risk to depressurize LPG to atmosphere even if a small volume?

It’s Pilesar. Everything has a risk associated with it! You have to manage the risks! To depressurize a small volume of LPG, be sure there is no ignition source, be sure everything is grounded, be sure the vapor cannot be trapped, release it slowly so it dissipates. Don’t breathe the fumes; move away to fresh air. Take an experienced operator or maintenance person with you.