Eddy Current (EC)

What is Eddy Current Testing?

Eddy Current Testing (EC or ECT) is an electromagnetic inspection method that can be applied to all electrically conductive materials. It is sometimes also referred to as "inductive testing".

 

The technique can be used for a variety of applications, such as:

 

  • Crack detection
  • Corrosion and material thickness measurement
  • Material sorting
  • Identification of heat-affected zones (HAZ)
  • Coating and layer thickness measurement
  • Evaluation of electrical conductivity
  • Metal detection

Eddy current testing equipment essentially consists of three main components: a generator, a probe coil, and a detection system, such as an ammeter or oscilloscope.

The generator produces an alternating current that flows through the probe coil. As this current flows through the coil, it generates a primary magnetic field around it. When the coil is placed over a conductive test piece, this magnetic field induces eddy currents on the material’s surface. These currents, in turn, create a secondary magnetic field that opposes the primary field. The strength of the secondary field relative to the primary one depends on the electrical and magnetic properties of the test material.

 

Advantages of Eddy Current Testing compared to other crack detection techniques:

✔ Fast method – No need for preparation or post-processing of the test object.
✔ No direct contact required – The probe coil does not need to touch the material, allowing inspections on painted surfaces and even in submerged environments.
✔ Low operating cost – No need for consumables.
✔ Automation possible – The technique can be used for high-volume inspections, enabling integration into automated systems.

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History of Eddy Current Testing

Between 1775 and 1900, scientists such as Coulomb, Ampère, Faraday, Ørsted, Arago, Maxwell, and Kelvin developed and documented most of the knowledge we have today about magnetism and electromagnetism. These principles form the foundation of modern electromagnetic non-destructive testing (NDT) methods.

  • 1820: Ørsted discovers the magnetic field generated by an electric current.
  • 1824: Arago observes that the oscillations of a magnetized pendulum are strongly dampened when near a non-magnetized conductive material.
  • 1831: Faraday formulates the principles of electromagnetic induction.
  • 1873: Maxwell consolidates these findings in his two-volume work, whose equations remain fundamental in electromagnetism research.

For a long time, these discoveries were not applied in industrial inspection. However, starting in the 1930s, significant progress was made, particularly by German scientist Dr. Friedrich Förster.

Dr. Förster conducted pioneering tests and established the theoretical foundations of eddy current testing. He also designed specialized equipment for this technique.

Since the early innovations of Dr. Förster, eddy current testing technology has rapidly advanced. Between 1975 and 1985, there were notable developments in both equipment design and application.

From the mid-1980s onward, the first microprocessor-based instruments appeared on the market, enabling inspection data storage, reference defect records, and indication logging during analysis.