7 replies to this topic

[R_Gowtham]

Hi all,

 

Is any code or standard or good engineering practice available to calculate PSV bypass line size? 

 

[breizh]

Hi ,

Please clarify , you can't  have bypass line on PSV . 

Thanks to describe your scenario.

Breizh

[R_Gowtham]

Please refer the below image. how to size the yellow highlighted line? 

 

is there any criteria?

Attached Files

•  bypass line.jpg   84.8KB   3 downloads

Edited by R_Gowtham, 08 June 2022 - 02:06 AM.

[breizh]

Hi,

Consider to read : https://www.cheresou...s-line-for-psv/

 

I don't  see the need for this line .

 

Breizh

[Bobby Strain]

It doesn't appear to be a PSV bypass. But a manual depressuring means, not meant to function as an alternate relief method. Most jurisdictions in the USA allow isolation valves with a single PSV. But a means of manned depressuring mechanism is required. Hence a "bypass" valve.

 

It seems your highlighted line is already sized.

 

Bobby

[Chemitofreak]

It is a manual depressurizing line. Minimum size used is 2" (same is specified in your P&ID). It can be based on the volume that needs to be depressurized. You should check your philosophy documents for guidance.  

[fallah]

Hi all,

 

Is any code or standard or good engineering practice available to calculate PSV bypass line size? 

 

Hi,

 

Although looks like it's a bypass, the purpose of the mentioned line which is mostly 2" size, isn't really as a PSV bypass. In fact, it is a connection from the vessel to the flare network for maintenance to allow purging when the vessel is out of service.

[abhi_agrawa]

This is not a bypass. PSV bypass is a misnomer in itself.

 

Personally, I call this depressuring line. I have used this line extensively during initial start-up. The usual scenario is:

a. You have a vessel filled with Nitrogen and you would like to introduce hydrocarbons in to this vessel.

b. When you introduce Hydrocarbons - where does this Nitrogen go? You cannot open the vent and vent to atmosphere as you may vent hydrocarbons as well, this is dangerous.

c. You need a connection to flare that can be opened to let this Nitrogen go to flare.

 

The line to be used is this so called PSV bypass.

 

The line size should be determined based on how fast you would like to bring in hydrocarbons. For large vessels 2" may not be adequate.

 

Hope this helps,

Abhishek