Detecting coils inside steel cylinders

[alan123hk]

Maybe you can try to do an experiment.

Just try to apply a frequency of about several kilohertz to several tens of kilohertz, and also try to adjust the current of the outer coil, you can study the data and evaluate the feasibility.

By the way, what is the thickness of the inner steel pipe?

 

[Tom.G]

What is the purpose of the outer pipe, does it transport anything, is it just a redundant container when the inner pipe fails, something else?

Details please! In engineering data/information is golden. So far we seem to be playing a game of "20-Questions".

 

[Fredbonyea]

OK how about a single coil that you resonate with a capacitor (probably best at low frequency). Using a signal generator/analyzer you could look at the Q as the coil is scanned down the pipe. Like a metal detector, sort of.

A steel pipe will conduct a local field via eddy currents. The conduction will be week, but at the right frequency, and with a differential detector, in most cases it is possible to detect a coil inside a steel barrier at very short distances.
Your source current must be very close to the pipe, preferably within a millimeter. The frequency of the source should be the same or a multiple of frequency of the resonant circuit you have constructed.
A differential detector could have two field coils, both butting the steel pipe at the same distance. What you would look for is small current variations between your two bridged fields as you pass the paired coils along the pipe, and it will be very small. The thicker the pipe, the more current you will need to couple the eddy currents.

 

[DaveE]

A steel pipe will conduct a local field via eddy currents. The conduction will be week, but at the right frequency, and with a differential detector, in most cases it is possible to detect a coil inside a steel barrier at very short distances.
Your source current must be very close to the pipe, preferably within a millimeter. The frequency of the source should be the same or a multiple of frequency of the resonant circuit you have constructed.
A differential detector could have two field coils, both butting the steel pipe at the same distance. What you would look for is small current variations between your two bridged fields as you pass the paired coils along the pipe, and it will be very small. The thicker the pipe, the more current you will need to couple the eddy currents.

This idea, like most in the thread doesn't work. We all thought he was looking for the presence or position of an internal coil. Later, we found out he is looking for physical damage (or not) to said coil, which means we have to evaluate structure, not just existence.

My latest idea: a portable x-ray machine.

 

[Averagesupernova]

My latest idea: Forget about this thread. Too much info is coming too late. No good description from the get-go. My question has still not been answered, so I say what's the point?

 

[kinsler33]

This calls for some experimentation. To an old-time radio engineer your steel pipe would provide your inner coil with splendid magnetic shielding, and to a first iteration it would do just that. If, however, you were able to provide an alternating magnetic field of sufficient magnitude to magnetically saturate your pipe, then the inner coil (which would not saturate magnetically) would feel that alternating magnetic field and produce some sort of signal in your outer coil.

All this is great except that you'll be looking for the tiniest of signals amid an enormous alternating field, and some exceptionally fancy electronics would likely be needed to filter out the slight distortions caused by the presence of your inner detector coil, and these would likely be swamped out by the hysteresis distortion of the waveform as it magnetically saturates your steel pipe.

Your essential task is to extract some sort of a signal from this assembly, but I don't think an electrical signal will be the best choice. I'd consider acoustics, for while you won't have access to the inner pipe after assembly you likely will be able to listen to the fluid flow down that pipe and also down the outer pipe.

If a single microphone is installed between the pipes you'd be able to hear the dam burst on that one. If you installed an additional microphone far upstream inside the inner pipe you'd be able to calculate the location of the break by measuring the time lapse between the inner mic's signal and the outer mic's signal. You'd need to know the speed of sound in the fluids involved.

 

[shjacks45]

Summary:: If I have a coil inside a piece of steel pipe, can I detect it from outside of the pipe using a tuned transmitter / receiver array?

Just some idle Sunday musings. I have a steel pipe that is 2" ID, 2.5" OD, 10' long. I want to place a coil inside the pipe midpoint along the pipe and detect it's presence with a transmitter / receiver array. The array can consist of two coils wrapped around the outside of the pipe and can be adjacent to the inner coil.

Can I detect the inner coil?

Depends on whethe your steel is magnetic or not. Some types of stainless steel are nonmagnetic.

 

[shjacks45]

My latest idea: Forget about this thread. Too much info is coming too late. No good description from the get-go. My question has still not been answered, so I say what's the point?

I worked for the City of Seattle Engineering Department and we routinely located water, sewer, and natural gas piping as well as electrical conduits. No one I know has successfully tried your method. Iron is magnetic and blocks magnetic fields. There are non-magnetic steels that might work. Since you didn't specify the steel I'll assume you have no idea so its probably cast iron.

 

[alan123hk]

Iron is magnetic and blocks magnetic fields. There are non-magnetic steels that might work

From a certain angle, it seems to block the magnetic field, but from another angle, its role is to guide the magnetic field to the inner coil wound on the inner pipe.

Therefore, if the OP cannot provide details, such as whether there will be a large non-magnetic conductive gap layer between the inner pipe and the outer pipe, the physical data of the relevant materials, and other necessary information, it is difficult to conduct a comprehensive feasibility assessment.