ECT Eddy current testing is a non-contact testing method, which mainly uses the electromagnetic field and electromagnetic induction between metals to detect. It is one of the NDT non-destructive testing methods in the industry.

The principle of eddy current testing is that the coil with alternating current is placed on the metal plate to be measured or outside the metal, tube to be measured (see figure). The alternating magnetic field will be generated inside and near the coil, which makes the induced alternating current in the sample appear to be eddy, which is called eddy current. Under certain conditions, the current through the coil is invariable. If the coil is close to the workpiece under test, like a ship in the water, the eddy current will be induced in the workpiece. Under the influence of the eddy current, the coil current will change. Because the size of the eddy current varies with the defect in the workpiece, the change of coil current can reflect the defect in the workpiece.