in this we will discuss about eddy current testing

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*EDDY CURRENT TETING
*By:
Zoha Nasir
Assistant professor
JIT, Barabanki

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Electromagnetic analysis is a term which describes the broad
spectrum of electronic test methods involving the intersection of
magnetic fields and circulatory currents. The most widely used
technique is eddy current method.
Eddy currents are composed of free electrons under the
influence of induced electromagnetic field which are made to
“drift” through metal.
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When an alternating current is passed through a coil, it
develops a magnetic field around the coil, which in turn
induces a voltage of opposite polarity in the coil and opposes
the flow of original current.
 If this coil is placed in such a way that the magnetic field
passes through an electrically conducting specimen, eddy
currents will be induced into the specimen.
The eddy currents create their own field which varies the
original field’s opposition to the flow of original current.
 The specimen’s susceptibility to eddy currents determines
the current flow through the coil.
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5. Eddy current inspection can frequently be performed without
removing the surface coatings such as primer, paint, and
anodized films.
It can be effective in detecting surface and subsurface
corrosion, pots and heat treat condition.
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Pulsed Eddy Current Technique
Transmission Method
Reflection Method
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Concentric Coil
Probe Type Coil
Bobbin Coil
Encircling Coil
Absolute And Differential Coil
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Low cost.
No final cleanup required.
ECI is very sensitive to small cracks and defects.
Equipment are portable.
Minimum part preparation required.
Applicable to both ferrous and non ferrous metals.
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Trained operators are generally required.
Surface finish and roughness may interfere.
Depth of penetration is limited.
Only applicable to conductive materials.
Interpretation may be difficult.
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In field of welding, casting, forging.
For crack detection.
Material thickness measurement.
online testing of wires and tubes.
Coating thickness measurement.
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Porosity.
Undercutting.
Rollover or “Cold Lap”.
Slag inclusion.
Poor penetration.
Voids.
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