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Eddy Current Testing

Eddy Current Testing


Eddy current inspection is one of several methods that use the principle of “electromagnetism” as the basis for conducting examinations. Several other methods such as Remote Field Testing (RFT), Flux Leakage and Barkhausen Noise also use this principle.

Eddy currents are created through a process called electromagnetic induction. When alternating current is applied to the conductor, such as copper wire, a magnetic field develops in and around the conductor. This magnetic field expands as the alternating current rises to maximum and collapses as the current is reduced to zero. If another electrical conductor is brought into the close proximity to this changing magnetic field, current will be induced in this second conductor. Eddy currents are induced electrical currents that flow in a circular path. They get their name from “eddies” that are formed when a liquid or gas flows in a circular path around obstacles when conditions are right.

Crack detection is one of the primaries uses of eddy current inspection. Cracks cause a disruption in the circular flow patterns of the eddy currents and weaken their strength.  This change in strength at the crack location can be detected.


Probes-Mode of Operations

Absolute Probes

Differential Probes

Reflection Probes

Hybrid Probes



Surface Probes

Bolt Hole Probes

ID or Bobbin Probes

OD or Encircling Coils

Array probes



Summary of applications:

  • Flaw detection, bolt hole cracks, welding, corrosion mapping, PT replacement
  • Material Sorting
  • Nonconductive coating thickness, paint, epoxies, ceramics
  • Conductive coating thickness, clad metals
  • Material/dimensional thickness gauging
  • Hardness measurements
  • Heat Exchanger -  Tube Inspections

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