Eddy Current Testing (ECT)

The foundation of ECT lies in electromagnetic induction, which is the study of the interaction between electricity and magnetism.  The probe (the housing for the test coil) is one of the three main parts of an eddy current (EC) system, along with the fault detector device and software. The test coils are made up of a tightly coiled wire (coil) in various configurations, producing an oscillating magnetic field when an alternating current travels through them. Eddy currents are created in a conductive test specimen when a probe makes contact with it, causing the specimen to generate its own magnetic field. According to Faraday’s law of electromagnetic induction, the kinetic energy of a moving magnetic field induces a voltage in a moving conductor.

The lift-off refers to the distance between the probe and the component, making inspection without having to remove paint possible if the lift-off is nullified. Industry regulations frequently recommend this technique for measuring coating thickness prior to other NDT techniques like magnetic particle testing. The AC field links the coil to the part in an EC inspection system without the use of materials like couplant (often required for ultrasonic testing). This allows the inspection to be carried out without the need for any supplementary materials, post-inspection cleaning, or removal of the coating on the tested component.

EC can calculate the volume of damage caused by an interruption and show the relative size of several depths. Conventional EC allows for precise sizing of indicators so long as the calibration is done correctly for the material and sensitivity. A trained inspector can then evaluate the location and severity of the indication based on the amplitude and impedance presented on the fault detector. To properly measure the depth of cracks, it is necessary to calibrate samples with known damage that are representative of the test subject. Material, thickness, and crack depth are crucial factors in EC technique depth sizing. Screening depths based on EC data are commonly utilized.

Disadvantages and Potentials of ECT include:

1. Slowness and a small service area

2. Limited to conductive materials

3. Needs to reach the surface

4. High levels of expertise and training

5. Surface polish and roughness

Alternative Electroconvulsive Therapy

Pulsed eddy current (PEC) relies on the phenomenon of electromagnetic induction to accomplish its goals. PEC includes a wider range of frequencies, allowing simultaneous measurements of a variety of depths and electromagnetic responses at a variety of frequencies. PEC can be performed without ever touching the workpiece’s surface, making it useful when the surface of an object is particularly rough or difficult to reach.

Magnetic Induction Array (ECA)

ECA and PEC have several potential uses in the business world, such as checking for corrosion and measuring steel thickness. They are versatile and can be applied to a wide variety of materials, including vessels, columns, storage tanks and spheres, piping systems, and structural applications.

Video 01: Eddy Current Testing