Leak Detection of Natural Gas Pipeline During Hydrostatic Test

"LNB-like probes"

????

PG&E Talk get it !

As far as I know, natural gas pipe lines should be checked by the API standard and there you have info about minimum pressure and time depending on wall thickness and outer diameter.

Isaac

I have not seen the instrument - LNB-like probes and laptop for signal processing. However if you have found leak by the instrument and not located on the line, effectiveness of any instrument is zero. Pressure indicator, pressure recorder, dead weight tester and recorded chart serves the same purpose whether line has leak or not. When there is no leak on the line no problem. But when you have reached to the decision that the line has leak somewhere that is problem - to locate the leak. If the pipeline is buried, experienced line walker's job starts. To locate leak on buried pipeline is a difficult job specially when the line is buried in sandy soil or in waterlogged area. For this reason precaution against leak and facilitating visual inspection to locate leak is given much importance during pipeline laying. I would narrate a Case History of pipeline leak and locating it. In 1983 I was handed over a project - 24" dia x 1.25" wall thickness, 56 KM pipeline buried in sand at Shedgum Gas Field, Saudi Arabia to write a hydrostatic test procedure and test it at 4000 psi. We found the leak through pressure recorder within 48 hours and located it after 45 days. It was leaking through the factory made anchor flange, water passing through the concrete block emerged by wetting two square foot on top of the soil and about 15 away from the concrete block. This means that what ever instrument you use to find leak in the line unless you locate the leak, instrument is just to log the pressure drop and arrive on decision whether it has leak or not.

dear friends

Actually I'm exactly aware of the hydrostatic test standards and also I'm somewhat familiar with some of the leak detection methods like tracer gas, penetrating radar and ... . But I've met some one that claims he can find leaks using electromagnetic waves. He says that by using these waves, he can find the location of leakage by finding the location of flaws in the pipe in addition to finding the places that there is a contact of water with the soil.

I want to know if you ever have heard about this and if yes, let me know it works.

Thanks a lot

Dear maryko, I have heard about these technique but not seen any one using it. But the emphasis remain on the visual inspection with these technique too. Once you have filled the line with water and without additive, then no option left but pressurize it till the leak is wide open, line burst or wetting the crown or run into the desert guessing the location of leak. Yes! when you are prepared and anticipate the leak, tracer gas is injected but again unless the tracer is smelled during walking, you are shooting in the dark.

I have used a similar technique to find leaks in an in-ground pool. The walls must be non-conductive, as in a vinyl lined pool. I doubt that it would work with most pipe materials of construction, I think even concrete may be too conductive. I'll describe how it works in the pool, and you can perhaps relate to the pipe.

Water in a pool is conductive. It is isolated from ground by the walls, with exception of any penetration in the wall such as a drain or a leak. If you apply a voltage to the water and the other end to the ground, current will flow through the water into the ground where leaks are located.

At these points, current and voltage fields are high. You look for leaks by an increase in current detected by a probe consisting of an ammeter with 2 electrodes about a foot apart in a piece of PVC pipe. You go over the interior surface of the pool (in the water). As you approach a leak, the current increases. When the PVC pipe probe is oriented so that the two sensor electrodes are in line between the voltage electrode in the water and the leak, the max. current is observed, which increases the closer you get to the leak.

Other penetrations such as vents give "false alarms" as will the voltage electrode placed in the water. However, these are pretty easy to sort out.

I could see how this would work if you had a way to remotely sweep the interior. I don't know if it would help by probing the outside dirt. Obviously, any metal pipe would not work. Concrete pipe maybe. Plastic pipe definitely.

Tad

It is easier to use the Ultrasound approach. Please go to the UE systems Inc. and can know more about motheds of detecting leakages.

sure, can you please?

Simple, by moving along the leakage line, the

detecting leakage device gives sound and visual signal. The signal intensifies as moves to the point of leakage. One can also use infra-red sensing device. The only problem is to be well trained to understand how to interpret the detected signal .

You might find a cheap version in the middle east. Seems the Iranians have a patented(?) hydrostatic tester (hydro static leak locator system for gas pipelines) that's pretty small. See the link below.

http://www.techpark.ir/?m=news&cat=84&pageNum_Recordset1=2&totalRows_Recordset1=195

hi.. I have never use this type of gas detection method , I have install a gas detector at my work area to detect the leakage of the gas.
https://www.aesolutions.com.au/products/gas-detectors-portable.php