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Api 520 Part Ii, Section 7.3.7.3

relief valves inlet line pressure drop 3% prv api 520

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#1 siewmoi_hong

siewmoi_hong

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Posted 05 September 2019 - 10:12 PM

Hi, I have a further question based on the following thread, but it has been archived.  i am creating this forum to further discuss my question:

https://www.cheresou...d-on-equipment/

 

The above query discussed about the statement made in API 520, Part II, 7.3.7.3

" When a pressure-relief valve is installed on a normally flowing process line, the 3 % limit should be applied to the sum of the loss in the normally nonflowing PRV inlet pipe and the incremental pressure loss in the process line caused by the flow through the PRV..."

 

If the scenario is a block outlet where all the blocked stream is directed to the PRV, is the "incremental pressure loss" mentioned above still applicable?

For example, at normal operation, the pressure drop at the process line is 5 psig between pressure source and PRV tap-off line.  When blocked outlet occurred, all the fluid is now diverted to the PRV.   PRV rated capacity results in pressure drop at process line = 7 psi, PRV inlet line = 4 psi.  

 

So this case, what is the inlet line pressure drop? 11 psi (7 + 4) OR 6 psi (7 - 5 + 4) (considered only "incremental" from the normal dP)

 

Appreciate your insight on this.

 

Thanks.

 

Regards,

SM

 

 

 



#2 fallah

fallah

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Posted 06 September 2019 - 08:25 AM

Hi, I have a further question based on the following thread, but it has been archived.  i am creating this forum to further discuss my question:

https://www.cheresou...d-on-equipment/

 

The above query discussed about the statement made in API 520, Part II, 7.3.7.3

" When a pressure-relief valve is installed on a normally flowing process line, the 3 % limit should be applied to the sum of the loss in the normally nonflowing PRV inlet pipe and the incremental pressure loss in the process line caused by the flow through the PRV..."

 

If the scenario is a block outlet where all the blocked stream is directed to the PRV, is the "incremental pressure loss" mentioned above still applicable?

For example, at normal operation, the pressure drop at the process line is 5 psig between pressure source and PRV tap-off line.  When blocked outlet occurred, all the fluid is now diverted to the PRV.   PRV rated capacity results in pressure drop at process line = 7 psi, PRV inlet line = 4 psi.  

 

So this case, what is the inlet line pressure drop? 11 psi (7 + 4) OR 6 psi (7 - 5 + 4) (considered only "incremental" from the normal dP)

 

SM,

 

For your case the 3% limit should be applied to (7-5+4) psi...



#3 siewmoi_hong

siewmoi_hong

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Posted 08 September 2019 - 06:59 PM

SM,

 

For your case the 3% limit should be applied to (7-5+4) psi...

 

 

Thanks Fallah.  






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