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Cost efficient pipe inspection solution

max_torch

Feb 9, 2014
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Putting the TLDR at the top here just in case the wall of text below dismays you:
What's a cheap and easy way to inspect and mark the location of leaks in a 5 kilometer long pipe section with no manholes in between?

On to the details:
We have a drainage system at my company which consists of HDPE pipes, 2 foot diameter, buried in the ground. We absolutely cannot have a leak in these pipes. We're talking potential shutdown of the company upon groundwater contamination. Thinking of using cameras in order to inspect for leaks. The longest pipe section that doesn't have any manhole access in between is five kilometers.

I am proposing to have a regular inspection and maintenance of the pipes in order to meet the vision of having no leaks. Once a leak is identified we will dig up only at the section where the leak was identified and patch it up with HDPE welding equipment (Which was also originally used to join the pipe segments). So far I have identified three possible options:

1. Craziest idea is to have a guy crawl into the pipes holding a camera. The guy will be fully covered head to toe. Not so sure if this is safe though. The problem is this will only work in the sections where manhole-to-manhole distance is sufficiently near so as not to endanger the person. There are pipe sections where there is no manhole for five kilometers. I really don't want to have to choose this option.

2. Robot-mounted camera. So far I haven't yet found where this can be bought, but I have seen DIY projects to make one, such as from instructables.com, and also examples of this kind of device on Youtube. I suppose for the five kilometer pipe section the way to go about it would be to have the remote control transmitter be at the manhole at the pipe opening, design the RF transmission to be unidirectional point-to-point between the robot and the transmitter propagating down through the pipe, and make sure that the RF transmission can reach at least 3 kilometers (to inspect the remaining portion, just deploy robot from the other side of the pipe section). Will it also make sense to choose a particular frequency that matches resonance to be optimized propagating down through a 2 foot wide pipe? Also attach a 3 kilometer rope to the robot just in case the RF signal gets lost so that the robot can be manually pulled out by hand.

3. Snake camera endoscope. So far the longest ive found available online has only been 100m in length. It wouldn't be possible to inspect the 5km long pipe section. But this is just a fiber-optic cable correct? And isnt it telecoms companies run kilometer long fiber-optic cables?

Would greatly appreciate anyone's additional ideas and suggestions. Selection criteria for the methodology would be cost, safety, speed, ease of operation, etc but weighted more towards cost and safety.
 

Harald Kapp

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A visual inspection, by whatever means, probably cannot turn up all possible leaks.Depending on the noxious stuff that is fed through the pipes a pinhole may be enough to contaminate the environment. Afaik, the classic method is a smoke test or a pressure test.
I suggest you get in contact with a company specialized in that kind of test. You'll probably have to repeat the test at regular intervals. Having a certified contractor do these test (and handing you a certificate with a "pass" stamp) will probably be your best chance to get away in case a leak happens anyway.

The safest (not the cheapest) solution would possibly encompass a double walled pipe with built-in leak detection.

Addendum: There may even be legal requirements to be considered if the pipe is used for noxious substances.
 
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Alec_t

Jul 7, 2015
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How deep is the pipework buried?
Is the 5k stretch reasonably straight with no obstructions?
Are there any hazardous residues in the pipe?
Can the pipework be totally emptied before an inspection?
Can it be pressurised to conduct an inspection?
 

duke37

Jan 9, 2011
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You do not say what the pipe is transporting. If it is a conductive liquid you could fill the pipe and electrically isolate the ends and measure the resistance to earth. If there is a leak, then the soil locally will be at a different voltage. Polyethylene is a good insulator and a Megger could check the overall resistance. A larger current may be needed to find the location of a leak.
 

Martaine2005

May 12, 2015
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We have a drainage system at my company which consists of HDPE pipes, 2 foot diameter
AFAIK, ground water does not contaminate drainage. The reverse is usually true, leaking drainage into the ground.
But a clean water SUPPLY can be contaminated via leaks at joints or damage. However, a small leak normally on a butt welded joint blows water out like a jet wash so dirt can’t enter. Damage by plant machines/diggers allows tonnes of soil/dirt etc into the pipe. The pipes usually have valves so sections can be replaced or isolated for pressure testing.
Most cost effective is to have inspection chambers where possible.
Or a ferret.

Martin
 

Bluejets

Oct 5, 2014
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AFAIK, ground water does not contaminate drainage. The reverse is usually true, leaking drainage into the ground.
But a clean water SUPPLY can be contaminated via leaks at joints or damage. However, a small leak normally on a butt welded joint blows water out like a jet wash so dirt can’t enter. Damage by plant machines/diggers allows tonnes of soil/dirt etc into the pipe. The pipes usually have valves so sections can be replaced or isolated for pressure testing.
Most cost effective is to have inspection chambers where possible.
Or a ferret.

Martin

Exactly, however an undetected water leak can certainly hit one in the pocket.
Friend of mine had an undetected water leak in a fire main (2" line) which cost him $4,000.00 in excess water fees.
I say undetected as the council were the only ones who had access to a newly installed radio meter which was locked away from vandals etc. so no way for my friend to realise he had a problem.
So much for chucking out the old mechanical meter simply because the council decide they don't want to get out of their car to read the meter.
I believe there are detectors that will identify a leak to a depth of around 600mm or so but the tried and true pressure drop still seems the best alternative for periodic before-the-event checks.
In Aus at least, plumbers pressurise a system over a week or so in new installs and it seems to work extremely well.
 

max_torch

Feb 9, 2014
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Need to post some corrections to the firs post detail:
Longest pipe section without man hole is only about 800meters, straight, no obstruction, this section is only 16 inches in diameter.
The rest of the other pipe sections, with length of about 140 meters between manholes, are 2 ft in diameter.

After reading first few replies I'm adding additional detail:
  • The pipe is a combination drain meaning it handles both rain water, and wastewater from draining inland fish ponds so the main contaminant would be organic waste. I would consider this as semi-risky hazardous residue and I will not expose someone to it without protection. Sad to say that other places require people to wade in this kind of muck without any protection at all(I've seen it but I don't condone it).
  • Pipework buried about 2 meters deep
  • the 800m stretch is completely straight without obstruction
  • Clean ground water can be pumped into the pipe to flush it out.
  • Pipes are not designed to withstand any pressure at all. These pipes are grooved at the exterior wall, wherein the pipe wall thickness at the grooves is thin.
  • @duke37 I have seen papers from IEEE database which detail a High voltage DC method for detecting leaks in polyethylene lined ponds. What you describe sounds similar to that method. I suppose multiple probes would have to be buried in the soil to narrow down the region containing the whereabouts of the large current.
 
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Nanren888

Nov 8, 2015
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For organic waste, combustable vapours, the equipment may have to be "intrinsically safe" as well as other certifications. Not sure you can megger a potentially explosive volume.
Not sure he meant large rather than just larger than a megger provides. You probably don't want to be putting large currents thorugh the ground if any people or livestock about.Potential difference should roughly steer you towards a single fault. Sort of depends on the soild types, too.
 

duke37

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Looks as if the electrical leak method has already been used in ponds. You will need a sufficient current if there is a leak to generate a potential gradiant in the ground. Some experiment would be necessary to find the current to give sufficient sensitivity - perhaps a few amps.

You do not need to bury ground probes, just use a probe on a reel of wire.
My brother did some experiments, putting an audio signal into the ground. I think he could detect this up to many metres if his transmitting electrodes were widely placed. The problem was mains hum from the neutral connection.

The pipe may well be sensitive to UV light and will split if embrittled so do not leave it in the sun.
 
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