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Flare Header Sizing


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#1 Sara Owens

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Posted 07 February 2019 - 02:16 PM

i am sizing the relief valve outlet lines. The outlet lines are connected to a flare header where the battery limit back pressure is minimum 2 psig and max of 65 psig.

how do i determine the relief valve outlet lines? At 65 psig max backpressure, this will be used to determine what type of relief valve selection, bellows, conventional, etc. when i make the flare backpresssure to 2 psig, i get a mach number of 1, which forces me to increase the line size. (when i use the 65 psig backpressure, I had no problem with the line size) what is the general practice to size the outlet lines to flare header? what is the rule of thumb for mach number on header and flare outlet lines? for the flare header and subheader, i want 0.5, and for the lateral outlet lines, i want to keep a mach number of 0.7. please let me know. 



#2 Bobby Strain

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Posted 07 February 2019 - 05:21 PM

Your employer should have procedures for you to use. If not, you should have a discussion with your supervisor.

 

Bobby



#3 fallah

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Posted 08 February 2019 - 05:38 AM

i am sizing the relief valve outlet lines. The outlet lines are connected to a flare header where the battery limit back pressure is minimum 2 psig and max of 65 psig.

how do i determine the relief valve outlet lines? At 65 psig max backpressure, this will be used to determine what type of relief valve selection, bellows, conventional, etc. when i make the flare backpresssure to 2 psig, i get a mach number of 1, which forces me to increase the line size. (when i use the 65 psig backpressure, I had no problem with the line size) what is the general practice to size the outlet lines to flare header? what is the rule of thumb for mach number on header and flare outlet lines? for the flare header and subheader, i want 0.5, and for the lateral outlet lines, i want to keep a mach number of 0.7. please let me know. 

 

Hi Sara,

 

General guidelines:

 

1- The mach no. values of 0.5 and 0.7 for headers/sub-headers and tail pipes are acceptable 

2- You should consider total back pressure (superimposed+built up) for PSV and relevant tail pipe sizing/selection

3- You should size the tail pipes for maximum back pressure

4- In the case of higher mach no. you should well support the tailpipe against subsequent vibration

5- As Bobby well mentioned you should have a discussion with your supervisor in this regard



#4 SyedAhmed

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Posted 08 February 2019 - 07:03 AM

You have a static pressure of 65 psig (flare header) and calculate the superimpose back pressure. 

In a conventional pressure relief valve application, built-up back pressure should not exceed 10% of the set pressure at 10% allowable over pressure. However, on the basis of total back pressure the type of PSV (Conventional, balance bellow or Pilot operated) can be selected.
 
0.7 mach number is general practice for tail pipe but need to concern with supervisor for project requirement.





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