Eddy Current Testing

Eddy current testing (ET) is a form of Non-destructive Testing (NDT) that uses electromagnetic induction to detect faults or flaws in conductive material. This includes weld inspections, sorting ferrous and nonferrous allows, identifying surface cracks in machine parts and metal stock, and detecting and quantifying corrosion.

Standard ET is based on electromagnetic induction, where a circular coil carrying an electric current is placed near material being tested. The alternating electric current in the coil generates a changing magnetic field which interacts with the tested material and creates an eddy current. These circulating eddy currents flow through the tested material, creating their own magnetic field, and then interact with the coil and its field by means of mutual inductance. Flaws in the tested material, such as changes in metal thickness and near-surface cracks, will interrupt or alter the amplitude and pattern of the eddy current and its magnetic field, identifying their presence.

An advantage of using ET is it can examine a large surface area quickly. In addition, it can also be used to inspect metal hardness and conductivity, and to measure thin layers of nonconductive coatings, like paint on metal parts. The main limitations to ET include only being able to test on conductive material, such as metal, which means other materials, such as plastic, cannot be tested using ET.