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Eddy-current testing
Eddy-current testing (also commonly seen as eddy current testing and ECT) is one of many electromagnetic testing methods used in nondestructive testing (NDT) making use of electromagnetic induction to detect and characterize surface and sub-surface flaws in conductive materials.
Eddy current testing (ECT) as a technique for testing finds its roots in electromagnetism. Eddy currents were first observed by François Arago in 1824, but French physicist Léon Foucault is credited with discovering them in 1855. ECT began largely as a result of the English scientist Michael Faraday's discovery of electromagnetic induction in 1831. Faraday discovered that when there is a closed path through which current can circulate and a time-varying magnetic field passes through a conductor (or vice versa), an electric current flows through this conductor.
In 1879, another English-born scientist, David Edward Hughes, demonstrated how the properties of a coil change when placed in contact with metals of different conductivity and permeability, which was applied to metallurgical sorting tests.
Much of the development of ECT as a nondestructive testing technique for industrial applications was carried out during World War II in Germany. Professor Friedrich Förster while working for the Kaiser-Wilhelm Institute (later the Kaiser Wilhelm Society) adapted eddy current technology to industrial use, developing instruments measuring conductivity and sorting mixed ferrous components. After the war, in 1948, Förster founded a company, now called the Foerster Group where he made great strides in developing practical ECT instruments and marketing them.
Eddy current testing is now a widely used and well understood inspection technique for flaw detection, as well as thickness and conductivity measurements.
Frost & Sullivan analysis in the global NDT equipment market in 2012 estimated the magnetic and electromagnetic NDT equipment market at $220 million, which includes conventional eddy current, magnetic particle inspection, eddy current array, and remote-field testing. This market is projected to grow at 7.5% compounded annual growth rate to approximately $315 million by 2016.
In its most basic form — the single-element ECT probe — a coil of conductive wire is excited with an alternating electric current. This wire coil produces an alternating magnetic field around itself. The magnetic field oscillates at the same frequency as the current running through the coil. When the coil approaches a conductive material, currents opposite to the ones in the coil are induced in the material — eddy currents.
Variations in the electrical conductivity and magnetic permeability of the test object, and the presence of defects causes a change in eddy current and a corresponding change in phase and amplitude that can be detected by measuring the impedance changes in the coil, which is a telltale sign of the presence of defects. This is the basis of standard (pancake coil) ECT. NDT kits can be used in the eddy current testing process.
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Eddy-current testing
Eddy-current testing (also commonly seen as eddy current testing and ECT) is one of many electromagnetic testing methods used in nondestructive testing (NDT) making use of electromagnetic induction to detect and characterize surface and sub-surface flaws in conductive materials.
Eddy current testing (ECT) as a technique for testing finds its roots in electromagnetism. Eddy currents were first observed by François Arago in 1824, but French physicist Léon Foucault is credited with discovering them in 1855. ECT began largely as a result of the English scientist Michael Faraday's discovery of electromagnetic induction in 1831. Faraday discovered that when there is a closed path through which current can circulate and a time-varying magnetic field passes through a conductor (or vice versa), an electric current flows through this conductor.
In 1879, another English-born scientist, David Edward Hughes, demonstrated how the properties of a coil change when placed in contact with metals of different conductivity and permeability, which was applied to metallurgical sorting tests.
Much of the development of ECT as a nondestructive testing technique for industrial applications was carried out during World War II in Germany. Professor Friedrich Förster while working for the Kaiser-Wilhelm Institute (later the Kaiser Wilhelm Society) adapted eddy current technology to industrial use, developing instruments measuring conductivity and sorting mixed ferrous components. After the war, in 1948, Förster founded a company, now called the Foerster Group where he made great strides in developing practical ECT instruments and marketing them.
Eddy current testing is now a widely used and well understood inspection technique for flaw detection, as well as thickness and conductivity measurements.
Frost & Sullivan analysis in the global NDT equipment market in 2012 estimated the magnetic and electromagnetic NDT equipment market at $220 million, which includes conventional eddy current, magnetic particle inspection, eddy current array, and remote-field testing. This market is projected to grow at 7.5% compounded annual growth rate to approximately $315 million by 2016.
In its most basic form — the single-element ECT probe — a coil of conductive wire is excited with an alternating electric current. This wire coil produces an alternating magnetic field around itself. The magnetic field oscillates at the same frequency as the current running through the coil. When the coil approaches a conductive material, currents opposite to the ones in the coil are induced in the material — eddy currents.
Variations in the electrical conductivity and magnetic permeability of the test object, and the presence of defects causes a change in eddy current and a corresponding change in phase and amplitude that can be detected by measuring the impedance changes in the coil, which is a telltale sign of the presence of defects. This is the basis of standard (pancake coil) ECT. NDT kits can be used in the eddy current testing process.