What happens to air in a hydrostatic test

AI Thread Summary
In a hydrostatic test, if air is present in an enclosed pipeline and pressure is increased, the air will dissolve into the water, especially at higher pressures like 150 PSI. The solubility of air in water increases significantly under pressure, allowing more air to be absorbed. If a contractor cannot find a leak and the pressure drops, it may indicate that air is present, but it will stabilize quickly if dissolved. A rough estimate of the air volume can be determined by the amount of water needed to eliminate the air pockets. Ultimately, at high pressures, the air can be fully absorbed, leaving no air pockets in the system.
Contractor
Messages
2
Reaction score
0
I am a contractor. I install water lines. Once installed we have to pressure test them. We pump the lines up to 150 PSI of water. If the PSI drops one of 2 things is wrong, either i have a leak in the line, or there is a small amount of air in the line. Generally if it is air, it stabilizes in a very short time and we get a passing test. I currently have a line that will not hold a test and I can not find the leak. My question is/are:

1. In an enclosed pipeline, supposing no leak, if there was air in the pipeline and i continue to hydrostatically pump until the pressure stops dropping, what happens to the air?

2. Is there a way to calculate how much air is in the line by how much water it takes to pump it up?
3. What is the air speed velocity of a coconut laden swallow (asking for a friend).
 
Physics news on Phys.org
With no expertise in the field...

1. The air dissolves into the water. At atmospheric pressure, not much dissolves. At 150 PSI, significantly more is able to dissolve. When you apply pressure, the bubbles slowly dissolve into the water and the pressure is reduced.

2. A good approximation would be that the volume of bubbles in the line is equal to the amount of water you pumped into make them go away.

3. African or European?
 
Your answer to 1 is very intriguing. So if i had 10 gallons of water and a gallon of air in the system, and then injected water up to 150 PSI and held it there, eventually all of the air would be absorbed into the water? so there would be no air pockets at all?

And I will counter you with, "Who is this man who is so learned in science?"
 
As I said, I am no expert. A quick trip to Google says that at 70 degrees Fahrenheit and 100 psig, the solubility of air in water is about 1 part in 7. That is, one gallon of air into seven gallons of water. So yes, one gallon of air would fit into ten gallons of water at 150 psig with no problem.

https://www.engineeringtoolbox.com/air-solubility-water-d_639.html
 
  • Like
Likes anorlunda
Hi there, im studying nanoscience at the university in Basel. Today I looked at the topic of intertial and non-inertial reference frames and the existence of fictitious forces. I understand that you call forces real in physics if they appear in interplay. Meaning that a force is real when there is the "actio" partner to the "reactio" partner. If this condition is not satisfied the force is not real. I also understand that if you specifically look at non-inertial reference frames you can...
I have recently been really interested in the derivation of Hamiltons Principle. On my research I found that with the term ##m \cdot \frac{d}{dt} (\frac{dr}{dt} \cdot \delta r) = 0## (1) one may derivate ##\delta \int (T - V) dt = 0## (2). The derivation itself I understood quiet good, but what I don't understand is where the equation (1) came from, because in my research it was just given and not derived from anywhere. Does anybody know where (1) comes from or why from it the...
Back
Top