What is Eddy Current Inspection

Eddy current testing is a non-destructive test method that can be performed on conductive materials. A test coil that is energized with alternating current is placed close to the test surface. This generates an alternating magnetic field that produces eddy currents in the test piece. Variations in eddy current flow produce a measurable change in the test coil. These changes are shown on a screen and interpreted to identify defects. The presence or absence of flaws in the test specimen can be determined by monitoring changes in the impedance of eddy current test coil. Changes in coil impedance are displayed as voltage changes in terms of signal amplitude and signal phase. These variations in phase angle and/or signal amplitude are correlated to flaw conditions, such as percent wall loss and volumetric wall loss.

 

Why is Eddy Current Inspection used

EC allows inspectors to find defects on the surface and subsurface level of an object easily and with a high degree of accuracy—but that’s just one of the reasons inspectors commonly use it to look for defects in a material.

  • It is incredibly versatile in terms of accuracy and portability/ease of use).
  • Its results are highly reliable, providing data of a high quality.
  • It is highly sensitive, allowing inspectors to identify defects as small as .5mm.
  • It is effective on surfaces that have paint or some other type of coating on them.
  • It can be used on high-temperature and underwater surfaces.
  • It provides immediate data.
  • It takes a relatively short amount of preparation time to perform (i.e., not much pre-cleaning or couplant is needed).
  • It can be automated for testing uniform parts, such as boiler tubes or wheels.
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