5 replies to this topic

[DoraeS]

Hi,

I would like to ask the following question:
When we determine the PSV minimum design temperature, do we consider the low temperature when relief fluid flashes across the PSV? In my previous project, we took the lead line minimum design temperature as the PSV min design temperature and did not consider the relief fluid outlet temperature.

 

Thanks.

[breizh]

http://satshamanagem...d-outlet-pipes/

 

Hi,

Consider the link above, in particular for the choice of MOC at the outlet .

Good luck

Breizh

[Chemitofreak]

Without a doubt you need to consider the low temperature during the relief case and define the MOC of the piping as per that.

 

I would suggest you use a simulation software for the same as most of the times the relief would be a mix of different components rather than a pure component.  

 

Also, you need to find the exact point up to which there will be the low temperature effect and define the MOC as per that. The low temperature can be up to the tail pipe, sub header, you need to calculate and find that. Just defining the MOC of the relief headers based on the MOC of the vessel will be a costly affair.

Edited by Chemitofreak, 10 August 2020 - 11:57 AM.

[Bobby Strain]

Common practice is to use materials suited to low temperature for the entire PSV.

[fallah]

 

I would like to ask the following question:
When we determine the PSV minimum design temperature, do we consider the low temperature when relief fluid flashes across the PSV? In my previous project, we took the lead line minimum design temperature as the PSV min design temperature and did not consider the relief fluid outlet temperature.

 

 

Hi,

 

Yes, you should do a low temperature study to consider the lowest temperature among flashing, j-t effect, auto refrigeration... for relevant component/line...

[Jiten_process]

In majority cases, PSV design conditions are aligned with vessel design condition on which it is located. For vessel, generally rigorous calculation is performed to derive lowest possible temperature and so the MDMT. The same conditions can be specified for PSV. In my view, even if you do simple flash calculation across the PSV due to pressure loss, the resultant low tempertaure would be higher than than rigorous MDMT calc performed for vessel. Hence, if you specify vessel MDMT for PSV, that would suffice.