Inleakage Test Performace

[isapiens]

Hi Everyone.

 

I am trying to perform a test on a system that will determine the integrity of the piping. It can be a pressure or a vacuum test.

My idea was to 1) Cap off one side of the system 2) pressurize the line or draw vacuum from the open end 3) trend the change of pressure over time (say 20 minutes)

 

Given that data i am a bit puzzled on how to calculate the "in-leakage" rate. I dont want that in-leakage to dilute my sample by more than say 10 percent.

I dont think i can use PV=nRT because it is not a enclosed system - i am adding air to it or air is escaping.

 

Please provide some guidence,

 

Let me know if you have other ideas on how to get the same result performing a different test.

Edited December 13, 2010 by isapiens

[CaptainPanic]

Hi Everyone.

 

I am trying to perform a test on a system that will determine the integrity of the piping. It can be a pressure or a vacuum test.

My idea was to 1) Cap off one side of the system 2) pressurize the line or draw vacuum from the open end 3) trend the change of pressure over time (say 20 minutes)

First of all, piping may withstand high pressure, but may not withstand vacuum.

Given that data i am a bit puzzled on how to calculate the "in-leakage" rate. I dont want that in-leakage to dilute my sample by more than say 10 percent.

I dont think i can use PV=nRT because it is not a enclosed system - i am adding air to it or air is escaping.

You can use PV=nRT to calculate how much air is entering or escaping if you know the change in pressure (and temperature, if that's relevant).

 

Please provide some guidence,

 

Let me know if you have other ideas on how to get the same result performing a different test.

You have to give a little more information - right now it's difficult to understand what you try to do. What's wrong with your data? What data do you measure? Pressure? Could there be a reaction with air? Can air dissolve into a liquid (like water)?

[isapiens]

Well, help me out with PV=nRT part.

 

I know that P(initial)V(initial)=nRT should be equal to P(finall)V(final)=nRT. Is that correct? I am not concerned with temperature because temp change in this case is negligible.

 

So after i pressurize the system I will get my P(initial). I am confused about the volume (init) and volume (final). Is the volume in this case, the volume inside of the piping or the valume of air? If it is the piping, then V would be constant and something else would need to change. If V is the volume of air, then i dont know how that changes... Or does air spread evenly, meaning R would change?

 

 

In regards to pressure vs vacuum, i am not really concerned because the piping is stainless steel and can withstand both. The system operates at slight vacuum anyway.

 

The data i am measuring is the change in P after I pressurize the system and cap it off on both sides, basically testing whether there is any air leakage or in-leakage.

[CaptainPanic]

Well, help me out with PV=nRT part.

Say please.

 

I know that P(initial)V(initial)=nRT should be equal to P(finall)V(final)=nRT. Is that correct? I am not concerned with temperature because temp change in this case is negligible.

 

So after i pressurize the system I will get my P(initial). I am confused about the volume (init) and volume (final). Is the volume in this case, the volume inside of the piping or the valume of air?

I use SI units... I hope you do too... otherwise you need to convert everything.

P = pressure in the pipe (Pascal)

V = the physical dimensions of the container - in this case the pipe. V is constant in this case. (m3)

n = amount of moles of gas in the container - if you have a leak, this is NOT constant!! (moles)

R = 8.3145 J/(mol K) - the gas constant. If you do stuff in English units, it's a different value. (J/(mol K))

T = temperature (in Kelvin!). Probably constant. (K)

 

So: P*V = n*R*T

Or: P/n = R*T/V = constant

(P/n)_initial = (P/n)_final

 

In short: a change in pressure is linearly dependent on the amount of moles of air entering, (n). And, since you want to know the amount of air entering your pipe, n is exactly what you need! And you're measuring P!

 

The data i am measuring is the change in P after I pressurize the system and cap it off on both sides, basically testing whether there is any air leakage or in-leakage.

 

You're good to go then. Good luck!

[isapiens]

Thank you for the response,

 

So n is going to be an unknown because i cant measure it. The only data i have is time vs pressure.

 

I am still confused how i am going to use the data i have (time vs pressure change) to come up with a leakage value.

 

I will work on it and see if i can come up with anything.

[CaptainPanic]

Thank you for the response,

 

So n is going to be an unknown because i cant measure it. The only data i have is time vs pressure.

 

I am still confused how i am going to use the data i have (time vs pressure change) to come up with a leakage value.

 

I will work on it and see if i can come up with anything.

Just calculate PV = nRT twice, please.

Once at the beginning. Once at the end. Both times your n is the only unknown. The difference between the two is how many moles of air leaked in or out of the pipe. And you're done.

Edited December 15, 2010 by CaptainPanic