Valve leakage rate 1

[Arman77]

Hi guys,

I am working on a project in the NGL plant and trying to calculate the leakge rate via a vlave, the upstream fluid is liquid with some associated vapour fraction.
I have the final leakage test pressure data after 45min of test.
also downstream volume in known and is fixed.
question is as liquid is passing through the valve it is flashing and making two phase mixture,therfore liquid by the time is compressing the vapour and pressure increases.
I want to know how to calculate leakage rate(both for the liq and gas mixture) under this condition? is still ideal gas law applicable?
any idea?

thanks

Mark

 

[JLSeagull]

I don't know about calculations. My guess is that you would test with atmospheric pressure on the valve outlet. I assume that you are dealing with metal seats. The outlet per API STD 598 would likely be vapor thus use the bubbles per minute rate.

 

[uu78hswang]

Control valve seat leakage testing is accomplished in accordance with FCI 70-2. Please refer his document, within this, there are six leakage classes defined ranging from Class I ,most allowable leakage, to Class VI ,the tightest requirement.

The leakage class most often specified with hard seated control valves is leakage class IV. Class IV leakage allows a leak rate equal to .01% of rated capacity.

 

[JLSeagull]

Control valve leakage rates are very different than block valve leakage rates.

API STD 598 includes maximum allowable leakage rates with a table by valve sizes and seat types. For all resilient seated valves the no leakage is permitted during the test duration. this means zero drops for liquid and zero bubbles for gas. For metal seated valves the per minute observation includs a limited quantity of liquid drops and gas bubbles based upon the body size. API STD 598 also includes tables with the duration based upon body size. Much more detail applies to the low and high pressure testing requirements related to valve materials and flange ratings.

Although not the lates copy, I use a downloaded copy of the Fisher Control Valve Handbook for the FCI 70-2 and IEC control valve seat leakage rates. The data in the control valve handbook may lack the latest standard changes.