Non-Destructive Testing (NDT) Practice Test

What type of current is primarily used in eddy current inspections?

1. Direct current (DC)

2. Alternating current (AC)

3. Pulsed current

4. Static current

The correct answer is: Alternating current (AC)

Eddy current inspections primarily utilize alternating current (AC) because of its ability to generate changing magnetic fields that induce eddy currents in conductive materials. This principle is fundamental to eddy current testing, as the presence of these induced currents allows for the detection of flaws, material properties, and conductivity variations within the test object. When AC flows through the test probe, it creates a dynamic magnetic field that penetrates the surface of the conductive material. As the magnetic field changes, it induces circulating currents—known as eddy currents—within the material. The characteristics of these eddy currents, such as their strength and patterns, provide valuable information about the integrity of the material, any surface or near-surface defects, and variations in material conductivity. Other options, such as direct current (DC), do not produce changing magnetic fields necessary for inducing the effective eddy currents required for inspection. Pulsed current can also be less effective in generating a stable field compared to the continuous flow of AC. Static current, being a constant flow, does not participate in the induction of eddy currents and therefore cannot be used for this type of inspection. Thus, alternating current is the optimal choice for conducting eddy current inspections.