Finding a leak location - underground 4in utility line 2

[thermmech]

Our 4" utility line has a bad leak.
Fluid: water
Pressure: 5 barg
Temperature: ambient (above 0 deg)
Pipe lenght: 800 m
Depth: 1 m, covered with 30 cm of concrete

The leak is quite bad indicating construction issue, and not corrosion. I am trying to understand capabilities of various inspection techniques to locate the leak. Pigging is not feasible. I have in mind either long range UT or eddy current testing.

Any advice on the most suitable technique, number of locations for excavation, etc. would be appreciated.

 

[LittleInch]

If you can't get access to the inside of the pipe, the options are fairly limited. Even if you can't pig, if you can insert a moveable plug then these can be activated at different points, but probably a bit excessive for a 4" line.

There are acoustic systems about - search acoustic leak detection - which you dig down, expose the pipe at certain intervals (50m?) and then they listen for the leak sound and gradually narrow it down using stereo connections. - typical see

http://ashtead-technology.com/productgroup/instruments/663/

The alternative is simply to dig down, break in and isolate at the 400m point, pressure up from one or both sides and find out which side the leak is, then half that distance and repeat and repeat until you identify a 15-20m lenght which you then just excavate the lot. A bit brutal, but effective. You don't say what the line is but if it is PE, then you can just squeeze it off to effect an isolation which it then recovers from.

If you have any fittings or connections on this line you could try those first.

Murphys law normally applies here which is that the leak will be in the worst possible location....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[stanweld]

I've used acoustics for leak detection of steel pipe with excellent results.

 

[rustbuster]

Ground penetrating radar might help to narrow down the leak location. Should be able to see the missing earth from the leak.

 

[LittleInch]

You could also try flushing and pumping through hot water and either get an IR camera or probe with temperature sensors. 30 cm of concrete pose an issue for most external sensing equipment. Need to get a breaker out.....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[thermmech]

Belated feedback:

We have used acoustic vibration successfully over the length > 800m. The leak was identified with +/- 5m accuracy.

Thank you all!

 

[inspect58]

If you could live with a reduced flow, you may consider cutting the line at each end, slide a 3" line inside the existing 4".

 

[Ripz]

Your suggestion of Long range Guided Wave UT would be best given the layout. It'll give you the location and you can excavate for followup. LRGW UT covers about 30 meters from the source. Different systems may be more.

Acoustic is good if you have a growing crack, but if you don't then that's pretty limited.