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#1
Old 07-02-2018, 05:21 PM
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Water used to test natural gas lines?

Very close to my house they are installing or upgrading natural gas lines. They had a sign about hydro testing. Is that using water or something else?

Also there were 3 pipes rather than 1, each around 10 inches in diameter . Is it common to have 3 pipes running next to each other? I assume this must be a major line to have 3 big pipes. The pipes are above ground now but I guess they get buried later.
#2
Old 07-02-2018, 05:27 PM
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They pressurize the line with water to see if it is welded / assembled correctly. Using water (instead of air) means that if the pipe fails, it doesn't become a bomb.
#3
Old 07-02-2018, 08:31 PM
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Also, water (often soapy water) is used to test gas pipe fittings after they are installed & pressurized.

The technician coats the fitting with it, and then looks for bubbles escaping. Much easier to see with the soap water covering the fitting. For other leaks, they often use an electronic sniffer. But when working on fittings, there is often an amount of loose gas around from when the fitting was disassembled or previously leaking, and that can confuse the sniffer. The bubble test is easy for an experienced technician.
#4
Old 07-03-2018, 08:31 AM
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These pipes run right through the middle of a set of townhouses instead of following a road. I suppose they were just taking a shortcut.
#5
Old 07-03-2018, 08:38 AM
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Same thing when boilers are tested. It is filled almost full with water then more air is pumped into the minor air pocket that is left. If there is a failure you get water spritzing out until the -- say -- two cubic feet if air at 200-psi expands expands to about 25 cf and the pressure drops to ambient. It's a lot safer than thousands of cubic feet of air trying to reach the new equilibrium.
#6
Old 07-03-2018, 09:50 AM
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Quote:
Originally Posted by DesertDog View Post
Same thing when boilers are tested. It is filled almost full with water then more air is pumped into the minor air pocket that is left. If there is a failure you get water spritzing out until the -- say -- two cubic feet if air at 200-psi expands expands to about 25 cf and the pressure drops to ambient. It's a lot safer than thousands of cubic feet of air trying to reach the new equilibrium.
Why would they use any air at all? two cubic feet of air @200 psi is still a lot of energy to dissipate, especially if there's a major rupture instead of a pinhole leak.

The OP might find this informative:
https://en.wikipedia.org/wiki/Hydros...peline_testing
#7
Old 07-03-2018, 09:58 AM
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Which came first...

Quote:
Originally Posted by Bijou Drains View Post
These pipes run right through the middle of a set of townhouses instead of following a road. I suppose they were just taking a shortcut.
More likely the pipeline was installed years ago, and the townhomes were built on top. It happens all the time.
#8
Old 07-03-2018, 10:13 AM
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I should add the townhomes are not directly on the pipes, there is a gap between buildings where the pipes run. .
#9
Old 07-03-2018, 10:15 AM
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Quote:
Originally Posted by Machine Elf View Post
Why would they use any air at all? two cubic feet of air @200 psi is still a lot of energy to dissipate, especially if there's a major rupture instead of a pinhole leak.
You can (almost) never get all the air out. Besides, itís all relative. Note the example given was a boiler that holds thousands of cubic feet. 2 cubic feet of 200 psi air isnít going to move tons of water very fast if it fails. When testing compressed air cylinders (think scuba or welding tanks) thereís maybe a cubic inch or 2 of air.

You want as small an air pocket as possible anyway. If itís too large, you wind up having to pump in lots of air to get the pressure up. When youíre using a hand pump, it can take just a couple of pumps to get the pressure up in a small volume. In a large volume, it takes much longer.
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