Unit -V EDDY CURRENT TETING * By: Zoha Nasir Assistant professor JIT, Barabanki 12/31/2016 Jahangirabad institute of technology1

^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. Eddy Current 12/31/2016 2

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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. Basic Principles 12/31/2016 Jahangirabad institute of technology4

^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. 12/31/2016 Jahangirabad institute of technology5

^ Pulsed Eddy Current Technique ^Transmission Method ^ Reflection Method 12/31/2016 Jahangirabad institute of technology6

^ Concentric Coil ^ Probe Type Coil ^Bobbin Coil ^ Encircling Coil ^ Absolute And Differential Coil Types Of Eddy Current 12/31/2016 7

^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. 12/31/2016 Jahangirabad institute of technology8

^ 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. 12/31/2016 Jahangirabad institute of technology9

^ In field of welding, casting, forging. ^For crack detection. ^Material thickness measurement. ^online testing of wires and tubes. ^ Coating thickness measurement. 12/31/2016 Jahangirabad institute of technology10

^ Porosity. ^Undercutting. ^Rollover or “Cold Lap”. ^Slag inclusion. ^Poor penetration. ^ Voids. Defects * 12/31/2016 Jahangirabad institute of technology11