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.
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.
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.
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.
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:
More likely the pipeline was installed years ago, and the townhomes were built on top. It happens all the time.
I should add the townhomes are not directly on the pipes, there is a gap between buildings where the pipes run. .
You can (almost) never get all the air out. Besides, it’s all relative. Note the example given was a boiler that holds thousands of cubic feet. 2 cubic feet of 200 psi air isn’t going to move tons of water very fast if it fails. When testing compressed air cylinders (think scuba or welding tanks) there’s maybe a cubic inch or 2 of air.
You want as small an air pocket as possible anyway. If it’s too large, you wind up having to pump in lots of air to get the pressure up. When you’re 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.