11 replies to this topic

[farhan ahmed]

I have come across a problem regarding the discharge line size of psv. 

 

PSV tail pipe is sized based on the Rated flow of PSV . Due to this Discharge line dia become higher than the main header.

 

Can we go for the larger  tail pipe size than the main header . Please give suggestion and codes and industry practices recommendations.

 

 

 

[fallah]

 

PSV tail pipe is sized based on the Rated flow of PSV . Due to this Discharge line dia become higher than the main header.

 

Can we go for the larger  tail pipe size than the main header . Please give suggestion and codes and industry practices recommendations.

 

Hi,

 

This can be happened if 1) there would be high difference between required and rated flow of PSV and 2) there is just one PSV at any time from which the relevant relief will be handled by flare main header and the relief from a PSV with highest required relief area has been considered as governing case.

 

In such rare case you can take the same size of PSV tail pipe for the main header...

[farhan ahmed]

Thanks Fallah 

 

Actually I am working on the existing flarenetwork and PSV to be added in the existing system. Here I want to avoid the changes in existing flare header. For this case , can I use the higher tail pipe size than the existing header size as I am considering rated flow in tail pipe.

[fallah]

Thanks Fallah 

 

Actually I am working on the existing flarenetwork and PSV to be added in the existing system. Here I want to avoid the changes in existing flare header. For this case , can I use the higher tail pipe size than the existing header size as I am considering rated flow in tail pipe.

 

You can, but the relieving bottleneck will be shifted from tail pipe to main header...!
 

[Sardar Shahnawaz]

Hi Farhan,

 

Please note that if you are having problem related to the back pressure and it resolves by increasing tail pipe size then it is OK, but you must also check velocity criteria for both header and tail pipe. 

[flarenuf]

hi farhan

what is your calculated size for the tailpipe and what is your size for the header?

 

normally the tailpipe is sized for rated flow but once it reaches the main header you should be using design flow.

what are you sizing the TP on , backpressure or velocity ?

the built up back pressure from the tie in to header back to the PSV outlet flange shouldn't be that large surely ?

is this PSV flowing individually or part of a scenario ?

are you saying you have to have a large diameter TP in order to meet BP limits on valve ?

conventional PSV ?

please give more info

 

brian

[Bobby Strain]

Seems that maybe you are not properly analyzing the system. If you provide details, we can all stop guessing.

 

Bobby

[S.AHMAD]

Agree with Bobby. Proper sizing and piping for psv  is critical in process units for safety reasons.

 

s.ahmad

Edited by S.AHMAD, 27 January 2016 - 03:38 PM.

[farhan ahmed]

Dear Flarenuf

 

what is your calculated size for the tailpipe and what is your size for the header?

Calculated tail pipe size is 14'' and header size is 10''

normally the tailpipe is sized for rated flow but once it reaches the main header you should be using design flow.

what are you sizing the TP on , backpressure or velocity ? I am considering Backpressure.

the built up back pressure from the tie in to header back to the PSV outlet flange shouldn't be that large surely ? Back pressure is increasing largely. 

is this PSV flowing individually or part of a scenario ? PSV  is flowing in blocked oulet case.individually and collectively in fire scenario.

are you saying you have to have a large diameter TP in order to meet BP limits on valve ? YES

conventional PSV ?YES

[Bobby Strain]

If you show us your calculation results, along with flow and properties, and a sketch with dimensions, maybe we can help. Something about your analysis seems wrong. But you fail to supply sufficient information.

 

Bobby

[flarenuf]

judging by the lack of response in over 2 weeks to bobbys comment on this topic Farnhan i guess you have found out where you have gone wrong in your calcs

thanks for the update

[christopherchoa]

Any updates Farnhan?