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Eddy current testing (ET):

 

In ET, a coil carrying an AC current is placed close to the specimen surface, or around the specimen. The current in the coil generates circulating eddy currents in the specimen close to the surface and these in turn affect the current in the coil by mutual induction. Flaws and material variations in the specimen affect the strength of the eddy currents. The presence of flaws, etc. is therefore measured by electrical changes in the exciting coil. Both voltage and phase changes can be measured, but some simpler instruments measure
only the voltage changes. The strength of the eddy currents produced depends on the:

 

  • electrical conductivity of the specimen

  • magnetic permeability (for a ferromagnetic specimen)

  • stand-off distance between the specimen and coil

  • AC frequency used in the exciting coil

  • dimensions of the coil and specimen

  • presence of flaws.

 

Much of the success of ET testing depends on separating the effects of these variables. Most eddy current instruments require calibration on a set of test specimens and the flaw sensitivity can be very high.

 

Equipment vary from simple portable meter-read-out instruments, to more complex oscilloscope read-out displaying both phase and voltage; recently the outputs have been digitized to produce fully automated computer programmed equipment with monitored outputs for high speed testing.

 

Applications vary from crack detection to rapid sorting of small components for either flaw, size variation, or material variation. Many applications are to bar, tube and wire testing. Metal sorting is also a common application of ET.

 

Limitations

 

  • Requires highly skilled operator
  • Applicable to conductive materials only
  • Depth of penetration in limited
  • Its application to ferromagnetic materials is difficult

 

Advantages

 

  • Gives instantaneous response
  • Can be easily automated
  • Versatile
  • No contact between the probe and the test specimen is essential
  • Its equipment can be made portable

 

Source: IAEA

 

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Useful links

 

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NASA Durban (Pty) Ltd.

 

Internationally approved NDT training and Certification. NASA has a clear vision to be the undisputed leader in Training, and Service, Amplified from the initial enquiry right up to developing you into a High Performance, Competent Technician.

American Society for Nondestructive Testing (ASNT)

 

The American Society for Nondestructive Testing, Inc. (ASNT) is the world’s largest technical society for nondestructive testing (NDT) professionals.

British Institute for Nondestructive Testing (BINDT)

 

The Institute’s aim is to promote the advancement of the science and practice of non-destructive testing (NDT), condition monitoring (CM), diagnostic engineering and all other materials and quality testing disciplines.

NDT Resource Center

 

This site was designed to be a comprehensive source of information and materials for NDT and NDE technical education. The site was created by nondestructive testing professionals and educators from around the world.

NDT.Net

 

Where expertise comes together - since 1996 - The Largest Open Access Portal of Nondestructive Testing (NDT) Conference Proceedings, Articles, News, Exhibition, Forum, Network and more.

NDT.Org

 

Jobs, News, Companies and Equipment for Industrial Inspection, Welding and Nondestructive Testing.

NDT.Ed.Org

 

Hosted by the Iowa State University center for nondestructive evaluation, the site is dedicated to NDT education.  

The International Atomic Energy Agency (IAEA)

 

The IAEA promotes the use of non-destructive testing technology to maintain the stringent quality control standards for the safe operation of nuclear and other industrial installations.

Radiation Control - South Africa

 

Radiation Control regulates all activities involving electronic generators of ionising radiation as well as radioactive sources used outside the nuclear fuel cycle.