Ultrasonic Leak Detection

I think it would, if your detector was very sensitive.

Why not just dunk it in a bucket of water and look for bubbles?

Compartment is 12 X 5 X 1 ft. and not something you would want to put in the water.

Specifically, I would like to know if airflow can be used as a carrier for an added ultrasonic

wave.

Thinking about it more I would say no. I believe the ultrasonic wave is completely in-dependent of the air flow. E.g. yelling help in a Hurricane would not transmit you yell miles away tot he next town in it's path. - Never mind.

Sound decays as the square of distance. So, if your detector was close enough it would pick it up.

See Sound intensity probe - Wikipedia, the free encyclopedia

You just sold an AccuTrak, where should they send the commission?

To the Volkswagen shareholders....Flushfernugen..

I'm not exactly sure I understand your question...but here goes.

Ultrasonic leak detectors detect the sound made by a gas escaping through the leak. The detector needs to be on the low pressure side. So if the compartment has positive pressure, it needs to be detected from the outside. Negative pressure needs the detector on the inside.

Does there have to be sonic flow for it to work? i.e. pressure inside > about 2bara, as it's atmospheric pressure outside. If so maybe the compartment can't take the pressure.

Yes, I thought after posting #8, flow may not need to be sonic to produce ultrasonic frequency.

an accurate description of what you're trying o achieve would yield a higher quality answer

Thanks for the replies. I apologize for the vagueness. At this point the objective is not important. I was curious about airflow being a carrier of an ultrasound wave.

However, The idea did cause thought of the pressure changing the mechanics of the compartment's ability to maintain air tightness under stress.

So why is the compartment under pressure in the first place, Mildred?

Actually the concept of ultrasonic leak detection using a transmitter and receiver has been around for sometime. There simply needs to be pathway, or source of the leak, for the wave to travel. Albeit a piece of paper can block the wave. However if there were a pin hole in the paper the receiver would pick it up. E.g. there are specific units designed for detecting hatch leaks in ships. These units usually operate in the milliwatt power range.

They typically operate at 40 KHz. My idea was to use a 40 khz ultrasonic cleaner transducer that operates at 50 watts. The transmitter is to be fitted with a directional or omni antenna, say e.g. 1 or 4 times the 8.6 mm wave length is on one side of test unit and the receiver on the other side using tube, horn or parabolic antenna - depending how accurate you need to be in location of the leak.

Regardless the geometry, if there is an air path, some of the 40 Khz will pass. Because of distance of travel through this unit the amplitude of the signal becomes the issue and sensitivity of the receiver.

Regarding the alternative i.e. looking for bubbles- Given the size of what I'm looking to test that be would lotta soap. LOL

be patient, his PHD is written with fresh ink

Nope, just some graphene and beer. It works.

I don't think using a transmitter is going to work. If the leak is big enough that 8.6mm sound waves will go through, you can probably put your finger in it.

It works and works well. Here is a piece on testing SeaCans as a preventative to water damaged cargo, http://www.sdthearmore.com/products/sdt-sherlog for underground tanks they vacuum the tank and listen for bubbles this can accommodate volatile and flammable contents. SDT is just one of several competent companies in this field.

OK, I stand corrected. Here is a leak detector that uses a transmitter. Learn something every day!

http://www.amprobe.com/amprobe/usen/hvac-tools/ultrasonic-leak/amp-tmuld-300.htm?pid=73418

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Amprobe TMULD-300 Ultrasonic Leak Detector with Transmitter

This is an amazing field in ND testing but very difficult to get it past ignorant management. In one case I was sent to change a noisy pump and it was very noisy but I listened to it and determined that the pump was just fine problem was cavitation due to the process pressures. (Propane in gas plant) saved them $ 15000.00 on these pumps 3 times in 6 months. Another time on a huge gas compressor some valves were failing and I was able to identify three out of 16 that were different in sound and they told me the savings over all by just replacing these was well over $ 100,000.00 yet they still could not see the advantage in utilizing this technology themselves. AGHHHHH.

Thanks for the reply. Yes, I have checked this unit out on the internet. I have a similar unit. It also operates in the milliwatts. I understand adding pressure to the test will only exacerbate and potential mechanical issues e.g. gaskets and loose sealant. So adding some pressure differential is good. Also. the sound generated by the emitter is specific as compared to a a random sound generated by a leak. I will be constructing a 50 watt emitter next month for testing. this should overcome most geometry and absorption issues.. All this discussion has certainly helped me align my thoughts and getting to a solid reasonable plan and approach.

Thanks you all.

The complete wave length is not needed. The receiver is capable of detecting only fractions of the original wave length.

Since you are using an emitter inside the enclosure the ultrasonic waves are not dependent upon the air flow for the detection of a leak. Barring the use of an emitter then a differential pressure is required and the ultrasonic detector will pick up the sound from the air (gas) flowing through the leak.

Either with or without an emitter; obviously, if any internal (or external pressure) differential is expected, then the enclosure should be tested with that pressure applied during leakage testing to see if pressure load deflections in the container's structure will result in leakage.

For any pressure tight structure, possible differential pressures created by any differential temperature between the internal and surrounding environmental temperature also need to be tested.

Really? I cant hear you!

Too much air in between!

Your posts stink!

So do you.

I think your mother is calling you.

Nope, I am not kidding you, nor Ideasmith. Really if the guy has some success on his project, it could even measure signature of "fart" and tell who's the culprit. That is the wildest capability of that instrument I could think of, although he works on a specific bandwidth. I do not understand why do you and your gang always rating me "off topic" on post, when there's validity on my point, thus CR4 tolerate that?

Now I want more than air in between! The internet is seemingly not wide enough for that one.

Unintentional farting is almost inevitable, but at least not deliberate, you know.

Thanks for the interesting replies.

This activity involves is static leak detection not pressure leak detection. I'm looking for potential leaks without the use of pressure. Not looking for microscopic leaks, not necessarily air tight, but should be water tight as in driving rain.

If there were pressure differentials involved they it would not exceed 15 psi.

The subject part is a panel made up of many fabricated parts. I need to determine, with out chambers, test walls or mock ups, would that panel as installed, leak air, and would leak water in a rain storm. BTW- re. previous replies, I do not need an instrument to know it leaked a fart.

I cannot use water, smoke or pressurization to perform the test.

It doesn't take a lot of pressure differential to generate enough of a flow through a pinhole that an ultrasonic detector can find it. I have found leaks in a gas-blanketed power transformer (it was deenergized at the time!) when the gas pressure was only 4-5 psi (which is typical for transformer gas blanket and gas regulator). The sound of the nitrogen escaping through the leak was clearly audible when I passed the detector near it.

I would assume adding an ultrasound source would work, but not necessary for the detector to dothe job. Just do a Google search for "ultrasonic leak detector" and you'll get lots of hits. Ours is from Ultraphonic, but there are many options.

Yes, as long as the beam was directed at the leaking area.

Thank you for the reply. In this case the signal frequency is "above" human detectable range.

My presumption is - If I increase the power of the emitter/transmitter. I increase the chances of picking up the signal from an air path e.g. .005" Diam. (?)

All ultra sound detectors work in the ultra sound range and the noise is created by the movement of the gas. The sound from a pin hole is local and will produce sound only if there is air movement however you can use the ultra sound generator to get same results if it can be placed in the tank. The ultra sound generated will leave through the hole and be detectable. There is some valuable training involved but even with out official training you will be able to detect leaks of a gas with ultrasound just with what the sales person can show you.

http://assets.tequipment.net/assets/1/26/Documents/Flir/applications-buildingenvelopes.pdf

E.g. would the escaping air act as a carrier of the ultrasonic wave?

I would be concerned that a very small leak might generate ultrasonic noise and create interference. Leave the pressures at atmospheric.

You apparently have the ultrasonic set up already. The better choice for what you are doing is a helium leak detector. We use them on tanks for vacuum processes.

Thanks for reply.