Eddy Current Testing (ET) is a versatile NDT method that can be used to detect (near) surface defects in conductive materials without removing the coating. An electromagnetic inductor is used to generate a magnetic field. When this field is introduced in the surface of the test piece, it generates so called "eddy currents" in the material. These currents generate their own magnetic field which resists the initial field created by the inductor. When a discontinuity disturbs the eddy currents, this can be registered by measuring the resulting change in impedance of the coil.
Besides detecting defects in the (near) surface, ET inspections can also be applied for material and coating thickness measurements, material identification and heat treatment monitoring.
No need to remove coating
Can be used to detect small cracks and other defects
Suitable for detecting surface and near surface defects
Immediate results on screen
Portable inspection equipment
Also suitable for coating thickness measurements, material identification and heat treatment monitoring
No significant surface preparation required
No need for couplant liquid or gel
Can be used to inspect objects with complex geometry
Can only be applied on conductive materials
Higher skill and training level required than with other techniques
Surface finish and roughness can cause false indications
Reference standards required for setup of the system
Limited depth penetration
Discontinuities that lie parallel to the probe coil winding and probe scan direction are undetectable
Unlike Magnetic Particle Inspection, Eddy Current Testing (ET) only measures disruptions in the conductivity of the material caused by defects. Since the created magnetic fields penetrate the coating layer, there usually is no need to remove the coating.