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Instantaneous Flow Rate Due To Choke Failure

instantaneous rate choke failure

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#1 SweAks

SweAks

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Posted 19 February 2015 - 10:52 AM

Hello,

 

I am sizing a pressure relief device on the manifold system. This is an onshore well pad, there is a choke (Choke 1) at the well head that reduces the pressure down to 4500 psig form 10,000 psig. Flow from the choke flow through the sand separator and then through another choke (Choke 2) at the line heater. The pressure is reduced from 4500 psig to 250 psig at Choke 2. The flow from Line Heater goes to Manifold and then to production/test separators. There is a PSV set at 1440 psig on the manifold to protect the manifold and downstream separators from Choke Failure and Blocked Outlet scenarios.

 

I evaluating the choke failure at Choke 2. Normal flow rate through this line is two phase mixture of 8 MMSCFD Gas and 40 BBLD Water. When i did the choke failure calculation, because of the high pressure difference (4500 psig to 1440 psig) at the choke and high Cv (35.5), i am getting huge flow rate of 145 MMSCFD of gas and 963 BBLD water. I understand this is an instantaneous rate and probably will only last for fraction of seconds, do we have to size the PSV for this instantaneous rate? The main problem is this PSV is relieving to Vent Knock Out Pot, now i need to size the Vent KO pot for this big rate. Thanks for your help.



#2 shan

shan

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Posted 19 February 2015 - 01:57 PM

1.  If you have wellhead master valve and wing valve as 2 SDV's controlled by independent PSHs, you may eliminate the PSV per Table A-3.2 (6) of API 14C.

2.  Max piping flow rate will be limited by Mach No. = 1.

3.  There is no problem to Vent KO pot because there is no liquid droplet requirement for vent release per 6.3 of API 521.






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