Dissolved Air Volume/Fill Volume vs. Hydrostatic Testing Pressure

[cornsnicker1]

Hello everyone,

I have an assignment to plot the volumetric ratio of air to water vs. the Hydrostatic Testing pressure for a pipeline hydrostatic test.

I have already researched Henry's law, but am struggling to find a volumetric variant of it and its equivalent constant to relate with pressure. Air trapped in the line also seems to vanish at a certain pressure (~600 psig?). How can dissolving oxygen be continuously a function of pressure if the air just sort of "snaps" into the water?

I would appreciate some direction.

Cheers!

 

[btrueblood]

some data here:

https://www.engineeringtoolbox.com/oxygen-solubility-water-d_841.html

 

[zdas04]

I think you've been sent on a fools errand. When you compare the amount of air that the water can dissolve to the volume of the line, the air-volume is way smaller than the error in the calculations (the Henry's law stuff is never better than ±20%, and I've found research that can't even agree on the direction that the constant changes with pressure).

The underlying issue is always "how much free gas is there in the hydrotest water that can collect in the high points?". The answer to that is indeterminate. I always fill the line with all the vents open and shut each vent when I get water out it. At the end of the fill, I leave the very highest vent open for 24 hours. Then I fill the line until I get water out the highest vent, and then go to each closed vent and open it until I get water. Then fill till the highest vent has water again, shut the highest vent and start the test. This technique has worked for tests in some pretty rough country in the Rockies. The only time it didn't work was when "the highest vent" was no where near the highest point in the line. We fought that test for a week before we got a good chart.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

Try and get a copy of BS PD 8010-1. Section 11.6.5

The air volume is found either by plotting pressure rise vs volume and then tracking back to zero pressure based on a straight line. Or plotting the pressurisation line and seeing how far out you are.

Air is 80% nitrogen....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[chicopee]

LI tell us more about D,t and the units used in eq. 19.