Underground Leakage Testing for 2" Pipe 500 meter Length.

Depending on the size of leak you're looking for, I would use water to pressurise the pipe and watch the pressure drop...

As to pinpointing where the leak(s) is/are there are various instruments on the market that can listen to leaking pressurised water pipes underground.

John.

water, oil, gas pipe? How deep. Does it leak now?

Put a cap on one end and a cap on the other with a valve and a meter on it. Put 10 PSI in the pipe, close valve tightly, and watch the meter for a week.

Value engineers? Did you know that value engineering is something...a kind of engineering, not related to your questions? Or did you mean, esteemed engineers?

45 years ago I saw an underground gas pipe tested . They capped one end, then had an arrangement of valves, a sight glass with water and a pressure source. The pipe and both sides of the sight glass were pressurized to the same source. Then the supply to the pipe was shut off. If there was any leakage it would bubble through the water and into the pipe to replace the leaking gas. I believe they used nitrogen from a bottle and dropped it to some reasonable pressure similar to the operating pressure of the pipe.

Hope this gives you some ideas.

The design pressure of the pipe needs to be stated.

Putting an innocuous liquid in the pipe would be preferable to using a gas; catastrophic rupture of a pipe containing a pressurised liquid is preferable to it containing a gas, as the energy released by the sudden expansion of the gas could cause injury or damage.

Were the fluid to be water, any loss of pressure would be accompanied by a wet spot somewhere near the leak, indicating where to excavate and repair.

In 1992 an elderly 6in cast-iron water main, already suspect and then overpressurised by the authorised commissioning of a new fire-water pump, caused the spectacular emission of several tonnes of mud and stones , and fracture and displacement of a 10m2 piece of reinforced roadway, causing much disruption to the road traffic at this pharmaceutical factory for several days. As a result of the incident, the location of the pipe section requiring repair became obvious. A colleague passing the location at the time of the rupture remarked, "It was great to watch", he said, "just like in Thunderbirds when the 'Mole' breaks through!" The culprit and the works maintenance engineer continued an excellent working relationship despite the disruption caused by this incident...

Portable Helium leak detector is usefull:pressurize the tube with helium ;make test with sniffer along the tube to set out the leakage diagramm .So you can find the leaks with a precision less then 0.5 m

First you need to determine if you want to carry out a simple leak test or if you need to do a strength test to a specified pressure related to a percenage of operating pressure. If you suspect a leak - that is you simply want to check if your pipe has been breached by mechanical damage or corrosion then you will easily verify that with a low pressure air test using a compressor or bank of nitrogen. Keep your air test no more than 20% of the normal operating pressure of the line or 20 psi whichever is less. Cap one end and put a gauge, tee and compressor fitting on the other. You will easily know of there is a leak and you will not get any catastrophic failure leading to serious damage or injury - take normal precautions and keep personnel away form the route of the line during the test. If as I suspect you need to re-certify the product line in accordance with a standard by carrying out a strength test then really you must employ a specialist. I cannot in a few lines explain to you the intricate details of strength testing and what constitutes acceptance criteria. Find a hydrostatic testing specialist company to carry out the test and certification for you. There are plenty around in malaysia.

The correct way to test the pipe is to do a hydro test. The pipe would be capped or valved off at each end. The pipe would be completely filled with water making sure there is no air or other gas trapped in the line. The pressure would then be raised to one and a half times the operating pressure and held for thirty minutes or an hour. There should be no pressure drop.

Testing the pipe at one and half times the operating pressure both checks for leaks and proves the integrity of the pipe.

You use water as a medium because it is not compressible and if you have a failure the instant the failure occurs all pressure is released.

Using air or other gas is dangerous because if you have a failure the compressed gas the gas will take a long time to be completely released and things (pieces of pipe, valves, etc) may blow a long way and can do a lot of damage to either people or equipment.

You may want to be careful that 1.5 times the operating pressure does not exceed the rated strength of the pipe material... Just a thought.

1.5 times operating pressure on a hydro test is not a leak test - that is a strength test. You WILL get a pressure drop and unless you pig the line while filling and carry out a P/V plot to determine air entrainment you will muddle around for a week trying to figure out if you have a leak or not. Low pressure air testing is a perfectly safe and normal way of leak testing and many standards provide the basis for methodology and acceptance criteria. My message is again to get an expert or you will hurt yourself, someone else or the pipe if you do not know exactly what you are doing. If none of that happens your QA people will not accept any test results as valid anyway.

I agree use an expert - there are a lot of inspection companies that specialise in pipe inspections. And too any inspection must follow the QA/QC guidelines.

If I was going to use a pipe that had not been used for several months and there was fear that it may have deteriorated to the point I feared a leak, then I would like that pipe line checked for it integrity (hydro test).

Check with the pipe manufacturer. They can provide specific guidance for testing there product. If it is a hydrostatic test any air (gas) entrained in the pipe will cause you difficulty. There are allowances to make up liquid volume lost to compression of entrained gas.

Pressure tests are always great fun.

Just an after thought. What is the "product" in the pipe?

If it is water or air then a small leak is not catastophic. If it is natural gas or gasoline then it is a huge issue.

Hydrostatic testing a natural gas line may not show leaks, but would prove strength. Since water is a larger molecule and more viscous than gas it would not prove leakage adequately for a gas.

The risk of failure would probably determine the end approach I would take. If it was a 2" water or air line at 100psi and risk of failure was small I would do a simple check and go use it. If it was for gasoline or high pressure natural gas I would take the situation very seriously and go for hydrostatic pressure testing and leakage testing by a certifying company.

I have observed that hydraulic systems in industry are routinely checked for leaks with high pressure nitrogen. It is rather noisy when a joint lets loose. However they can do a simple ultrasonic check for leaks. I believe final hydrostatic testing is done with oil. Again I have seen 100 gal of oil lost to the basement.

Your local gas company or water company may have the instrumentation necessary for these tests or tell you who does their testing for them. A hydraulic company will have test equipment suitable for hydraulic systems.

Your pipe contains roughly 430 cubic feet at one atmosphere. Block the other end with a leak free plug. Connect clean, dry compressed air to your pipe (with no leaks at your connection) and locate a gauge close to the point of connection.

1. Pressurize to 15 psig. You now have roughly 430 cubic feet of air above atmosphere. Close a ball valve or similar shut off to block further flow and note the time. Observe the gage for a few minutes.
2. If the pipe holds the pressure and the gauge stays at 15 psig 10 minutes, Congratulations. Check it again in one hour.
3. If the pressure drops from 15 psig to 10 psig in 10 minutes you have a big leak as in replace this darn leaky 2" pipe.
4. If the pressure drops to 14 psig in 10 minutes you have leaks roughly equal to a 3/8" orifice.

If by "pin point" the leak you mean identify roughly where they are you might fashion a bladder (from a bicycle inner tube or similar) to the end of a 1/2 or 3/4" hose. This assembly must not leak.

Feed the hose a known length into your pipe and pressurize the bladder through the hose to block pressure. Repeat steps 1 and 2. The bladder position affects the volume so the decay rate will change but with patience and effort you should find most of the leaks and know roughly where to dig.

As an alternative to digging there may be a fluid sealer that would be used to seal leaks as it flows into and through them similar to the automotive tire sealants.

Tom Kreher

I see you have a many good answers here. Is there any information regarding the rated working pressure of the pipe. You do have two options, a hydrostatic test or an air pressure test. I would opt for the air pressure test seeing that currently there is no product in the pipe. If the normal product in the pipe is other than water, air would be the easiest. On testing a pipe, any pressure drop is seen as a failure. I would use 2 psi. for a period of 2 hrs. This is consistant with our specifications for pipe testing and interstitial space testing. The method would be using a pipe cap for both ends, one with an air pressure gauge fitting and one the other with an air compressor fitting with a ball valve for isolation. Monitor the gauge for 2 hours @ 2 psi. If you feel comfortable over 2 hours then make the duration whatever you feel comfortable with. To me the duration should depend on the pipe coupling method. Welded, mechanical or glued etc.

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