Eliminate Gas Blow-by PSV

[patchlam]

Hi fellow engineers,

May I ask if we are allowed to eliminate Gas Blow-by PSVs by having a level transmitter and a shutdown valve which closes during low level detected?

Thank you for your time.

 

[LittleInch]

Not as a blanket rule no.

You may be able to argue this is an equivalent level of safety, but each design is its own.

So depending on what would happen if the blowby occurs, what the consequences of that are and what SIL level is required to prevent it.

PSVs are very reliable and relatively cheap. SIL 3 or 4 loops require multiple sensors, a logic solver rated to the same level of redundancy / reliability and similar for the shutdown valve itself.

For me you should have one of these (TX and S/D valve) already to prevent the issue and then the PSV takes care of what happens if it all goes wrong

 

[shvet]

@patchlam

We practice such regularly for similar issue for governing cases as all industry practicies/codes prohibit double jeopardy.
We install a shutoff valve upstream of a large column reboiler connected to a 2oo3 pressure sensor at the column overhead. This allows us to justify ignoring uncontrolled heat input case.
Sometimes we practice such for liquid level control (as you described), but only for minor cases, as we have a consensus that a level trip is not equial to a PSV from the point of ultimate reliability of the whole system.

As per my experience in industry such issues are site specific and case specific both and are subject to a local practice or philosophy. As per my experience some companies fully refuse such practice while some practice constantly.

 

[patchlam]

Apologies for my late reply. Thank you so much

LittleInch​

shvet​

for your comments. I was trying to find if SIL3 Level indicator ESD function will be enough to prevent the blowby and eliminate the PSV. But I found nothing.