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Leak Detection and Testing with Hydrogen Tracer Gas

Leak Testing




THE GAS / How do I get hold of 5%H2/95%N2 tracer gas?

CALIBRATION / How do I calibrate my hydrogen leak detector?

SAFETY / How can it be safe to use a mix of 5% hydrogen in nitrogen when the Lower Explosion Limit (LEL) for hydrogen is 4%?

THE GAS / What does the tracer gas mix, 5% Hydrogen in Nitrogen, cost and how much will I consume ?

THE SENSOR / How often must I change the sensor ?

METHOD / When should I choose a tracer gas method instead of pressure decay ?

EFFICENCY / I work with manual leak locating and have an H2000 detector. Do you have any good ideas or experiences on how to become even more efficient ?

THE GAS / Can the hydrogen and nitrogen separate? If so is there a possibility of accumulating dangerous levels in my building?

LEAK DETECTION / How small leaks can I find with hydrogen tracer gas?




THE GAS / How do I get hold of 5%H2/95%N2 tracer gas?

ANSWER:

Contact your local gas supplier and ask for the standard 5% Hydrogen in Nitrogen mix. It is commonly used as a shielding gas for welding and other industrial applications and goes by names such as - Formier5 or Formiergas 5/95 (AGA/Linde) - Naton-5, Nidron5 (France) - N2-H2 95/5 (Air Liquide) The gas supplier sometimes tries to sell you a very expensive specially mixed gas. The price for this one is many times higher than the standard 5%H2 in Nitrogen mix. Do not accept this and insist on getting the standard industrial grade mix. The non-negotiated gas price should be about 0,01 Euro per liters.



CALIBRATION / How do I calibrate my hydrogen leak detector?

ANSWER:

There are two ways to calibrate our hydrogen leak detectors; With a reference gas or a reference leak. The reference gas, available at gas suppliers, has a known concentration of hydrogen (recommend 10 ppm) which is used to calibrate the leak detector. A reference leak, supplied by Adixen Sensistor, has a fixed leak rate (flow or g/y) which is used to calibrate the detector. Both methods take less then 2 minutes to perform.



SAFETY / How can it be safe to use a mix of 5% hydrogen in nitrogen when the Lower Explosion Limit (LEL) for hydrogen is 4%?

ANSWER:

It is the nitrogen that does the trick. No combustion can take place without oxygen. The 4% limit refers to hydrogen in air which contains oxygen. When the 5% hydrogen/nitrogen mix is released into the air it dilutes the air. No matter how much you release, there will either be too little hydrogen or too little oxygen to allow the gas to ignite. Any mix of hydrogen and nitrogen containing less than 5.7% hydrogen is classified as a non-flammable gas. The safety margin is actually greater than that. Even a 10% hydrogen/nitrogen mix is extremely difficult (but not impossible) to ignite.



THE GAS / What does the tracer gas mix, 5% Hydrogen in Nitrogen, cost and how much will I consume ?

ANSWER:

The Hydrogen gas-mix costs about 5 USD per 1000 liters which makes it the least expensive tracer gas of all. How much you will have to use depends on what you are using it for. You can calculate the gas per test by knowing the internal volume of the object and the pressure used at the test. Then you just multiply by the number of test per day/month/year and you will get your consumption figure.



THE SENSOR / How often must I change the sensor ?

ANSWER:

Normally twice a year at continuous use. But in many cases less than once a year. It´s like answering "How long will a light-bulb last?." The sensor is not used up in the same sense as a light bulb but it ages and may become insensitive over time. It all depends on how much you use it.



METHOD / When should I choose a tracer gas method instead of pressure decay ?

ANSWER:

a) when you are looking for leaks smaller than what pressure decay can find.
b) when you have variations in temperature in your test objects
c) when you have soft objects
d) where you risk having leaking connections
e) when you also want to locate your leaks



EFFICENCY / I work with manual leak locating and have an H2000 detector. Do you have any good ideas or experiences on how to become even more efficient ?

ANSWER:

For certain applications you can speed up the process by using a bit of plastic foam, 5mm thick and of open cell type. If you apply the foam around for example a tube joint, it is often enough just sticking the probe into the foam at one point and get a gas indication even if the leak is on the other side of the tube. This is of course dependant on the dimension of the tube in question. You will have to try this specifically for your case. The reason why this happens is that the foam does not hinder but actually protects the gas from being vented away by the normal movements (draft) of the air. The gas seeps throughout the foam which will give you a gas indication whereafter you can remove the foam and start locating the leak. The foam actually gives you a fast and early indication if it is worth while to search the entire joint. Try it out and please let us know what you think about it.



THE GAS / Can the hydrogen and nitrogen separate? If so is there a possibility of accumulating dangerous levels in my building?

ANSWER:

Hydrogen and nitrogen are totally soluble in each other. Once mixed they will not naturally separate. Even heavy gases properly mixed will stay mixed. Carbon dioxide, for example, is a heavy gas and will stay at floor level, however when properly mixed with the air, it will not exhibit this feature. Even liquids, if totally soluble in each other, stay mixed. For example, no matter how long you left a bottle of liquor standing up, the alcohol, which is lighter than water, will not float to the top



LEAK DETECTION / How small leaks can I find with hydrogen tracer gas?

ANSWER:

It depends on the way you do the test. If you move the sensor probe along the surface of your test object you can detect leaks down to 5 x 10E-7 cc/s (equivalent to 0.1 g/y refrigerant gas). If you use a clam shell type of arrangement (locally enclosing the test point) you may detect leaks down to 2.5 x 10 E-6 (equivalent to 0.5 g/y refrigerant). If you need to do an integral test on the entire object in order to detect leaks from anywhere on the object you will have to use an accumulation chamber. The sensitivity will then be proportional to the time you allow gas to accumulate in the chamber and inversely proportional to the air volume into which the gas spreads.



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