What happens to air in a hydrostatic test

In summary, the conversation discusses the process of pressure testing water lines and how air can affect the results. It is noted that air can dissolve into water under pressure and that the volume of bubbles in the line can be approximated by the amount of water pumped. The conversation also includes a humorous question about the air speed velocity of a coconut laden swallow. The expert provides a link to information about the solubility of air in water and explains how it relates to the discussion.
  • #1
Contractor
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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).
 
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  • #2
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?
 
  • #3
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?"
 
  • #4
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
 
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1. What is a hydrostatic test?

A hydrostatic test is a method used to check the strength and integrity of a vessel or system by pressurizing it with a liquid, typically water. This test is commonly used in industries such as construction, plumbing, and oil and gas.

2. How does a hydrostatic test work?

In a hydrostatic test, the vessel or system is filled with water and then pressurized to a predetermined level. The pressure is then held for a specified amount of time to check for any leaks or abnormalities. The test is typically performed with the liquid at room temperature.

3. What happens to air during a hydrostatic test?

Air is typically removed from the vessel or system before the hydrostatic test begins. This is because air is compressible and can affect the accuracy of the test. Any air trapped in the vessel or system may also cause false readings or lead to potential damage.

4. Why is a hydrostatic test important?

A hydrostatic test is important because it ensures the safety and reliability of the vessel or system being tested. It helps to identify any weak points or defects that could lead to failure or accidents in the future. It is also a requirement for many industries and regulatory agencies.

5. Can a hydrostatic test damage the vessel or system?

A hydrostatic test is designed to put the vessel or system under a higher than normal pressure, but it is carefully controlled and monitored to prevent any damage. However, if the vessel or system is not in good condition or if the pressure is not properly managed, there is a possibility of damage. This is why it is important to have a trained professional conduct the test.

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