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Technique to detect thin metal film break?

  1. Mar 31, 2009 #1
    The thin metal film is scored with some pattern to 50-80% of its thickness. When exerted shear stress, the film will crack/open at score. I wonder what simple/practical techniques can be used to detect its pinhole or opening in real time?
     
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  3. Mar 31, 2009 #2

    Ranger Mike

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    Micromagnetic Method (Barkhausen Noise Analysis)
     
  4. Mar 31, 2009 #3

    Andy Resnick

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    Electrical resistance?
     
  5. Mar 31, 2009 #4

    Ranger Mike

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    this is a technique we use to check for grind burn when making gears..the gear grinder may over heat the metal during machining and cause sub surface flaws that can not be detected.

    so by placing a probe on the surface and generating flux lines ( alternating) you then use another probe to scan the surface..and check for resistance..a good gear will have a low current reading since the surface is a good conductor
    a flawed or cracked surface will require more current..and you have indication of cracks..
     
  6. Mar 31, 2009 #5
    Thank you. Our thin metal disc is used inside a pipeline and block fluid from one side to the other. When over pressure, it breaks at score and release fluid. Need to send fail-safe signal as breaking.

    This method also report peak signal in score area without breaking through. I also hope to use some non-moving part ( no scan) as detector and donot use analysis tools (idealy by using electric circuitry and filter or bridges)

    Any simple technology can be applied, which is sensitive to examining metal film (0.005 inch in thickness or so) rupture (break-through, not surface crack) ?
     
  7. Mar 31, 2009 #6
    Thank you , Andy.

    Do you have some idea on how to measure the change in resistance of such disc (say 6in in diameter and 0.005in in thickness)? The resistivity of metal is about 10E-8. This is a nice idea (simple to implement) if I find a way to measure the R properly.
     
  8. Mar 31, 2009 #7
    Do you mean 1.0 x 10^-8 ohm meters? (copper is about 1.5 x 10^-8 ohm meters) Is this a measurement prior to installation, or an in-situ measurement? Is this a magnetic or non magnetic material (e.g., nickel or copper) ? Are you looking for scores or pinholes? How long a score? I presume this is a non-contact measurement. Eddy current tests in the 10-100 kHz using a ferrite pickup are a good way for detecting scores, but not pinholes.
     
  9. Mar 31, 2009 #8

    MATLABdude

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    Bright light or laser shining through or being reflected off of the metal? You could pick up the light with a photodiode.
     
  10. Mar 31, 2009 #9

    Andy Resnick

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    I'm vaguely familiar with your application, but not the specifics. I was assuming some sort of rapid and catastrophic rupture occurs, so I was just thinking to apply contacts on either side of the score- when the disc ruptures, the resistance would very rapidly increase.

    Engineering fail-safe signals is not something I have experinece with, tho.

    It should be easy enough to establish a proof-of-concept with a simple multimeter and a couple of leads.
     
  11. Mar 31, 2009 #10
    My application is:

    1. Disc material is stainless steel (resistivity is 7.5E-7ohm-m, non magnetic) but sometimes uses nickel (magnetic).

    2. The examination is done when it is installed in the pipeline but we can isolate the disc from the disc at the flange.

    3. Score is pre-made and I am not to detect it. It is a circular line on the surface. If there is weakness on some part of the score and further into a pinhole, that is the part to inspect.

    4. If the disc is full open at all area of the score I can detect so my problem is only to detect if there is pinhole on the score.

    5. I try to look for either electrical or electromagnetic technology in use, but did not find a way out.
     
  12. Mar 31, 2009 #11
  13. Mar 31, 2009 #12
    Are you talking about detecting it while it is opening, or before it opens? Will this detection device be installed 100% of the time or used only during inspection? Can something be attached to the foil, or is this a non-contact measurement? What is the pressure difference across this foil? I have seen foils like this used up to 15 psi (vacuum).
     
  14. Apr 2, 2009 #13
    I detect the disc immediately after a opening (either fully tearing at score or a small slit/pinhole, the latter is for this discussion) and the examination is continuous during pipeline process for maybe 24 hours or more. One side of the film is fluid (liquid or gas) the other is atmeosphere. Sensor can be attached to the foil and it should only at the atmosphere side.

    So I hope some simply, small power consumption sensing element will work for this.

    1. Is Eddy Current probe suitable for continuous working without overheat problem?
    2. Can piezo-electric and/or acoustic work for it? If fluid come out of the film, the vibration character is changed. If so, where I can find the dynamic model to start with, and is it easy to filter the pipe noise?
     
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