Eddy current testing for coating thickness measurement of non-conductive layers
Eddy current testing measures the thickness of non-conductive coatings on metal by measuring the impedance change of a coil.
Physical-Chemical Mechanism of Action
Eddy current testing uses a coil that generates an alternating current. This current induces a magnetic field in the non-conductive coating. The coil impedance changes depending on the coating thickness and the distance to the conductive metal substrate.
Metallurgical Relevance & Welding Risks
Eddy current testing is especially useful for checking paints, epoxies, or other non-conductive coatings on metal. Incorrect measurements can lead to wrong results, which in turn causes inaccurate estimates of coating thickness. This can lead to welding problems, such as lack of protection or severe distortion of the metal.
Workshop Practice & Action Instructions
To perform eddy current testing correctly, the coil must be positioned so that it is parallel to the coating surface. The measurement should be done in a quiet environment to minimize interference. Reference values for impedance vary by material and application, but typically range between 50 and 200 ohms.