Which of the following discontinuities is easiest to detect with an eddy current test?

The rationale for the choice emphasizing the radial crack that extends to the outer surface of a rod as the easiest to detect with an eddy current test lies in the principles of eddy current testing itself. Eddy current testing involves inducing electrical currents (eddy currents) into the material being evaluated. These currents flow in loops perpendicular to the magnetic field and are sensitive to changes in material properties.

When a radial crack extends to the outer surface of a rod, it creates a significant disruption in the eddy current flow, which is readily detectable. The surface-level interruption ensures that the eddy currents cannot flow normally, leading to noticeable changes in the impedance and signal response observed during testing. The closer the discontinuity is to the surface, the more effectively the eddy currents can detect it, making this scenario particularly favorable for detection.

Conversely, other discontinuities may or may not produce noticeable signals depending on their nature and location. A crack parallel to the direction of the eddy current flow can lead to less disruption of those flows, potentially making it harder to detect. Discontinuities that are located deep within the material or at the center of a thick diameter rod may not interact significantly with the eddy currents at the surface, resulting in muted or undetectable