What kind of discontinuities can eddy current testing typically identify within conductive materials?

Eddy current testing is a highly effective nondestructive testing method used primarily to identify discontinuities in conductive materials. One of its key strengths is the ability to detect both surface and subsurface defects. This is made possible through the principle of electromagnetic induction, where an alternating current induces eddy currents in the material being tested.

When these eddy currents encounter discontinuities such as cracks, lifts, or changes in material properties, they cause a change in the impedance of the coil used in the test. This change can be detected and interpreted, allowing technicians to ascertain the presence and extent of the defect. Surface defects are more easily detected due to their direct interaction with the eddy currents; however, certain configurations and testing techniques can also reveal subsurface defects.

In contrast, options indicating that only internal defects or only surface irregularities can be identified limit the scope of what eddy current testing can accomplish. The detection of air gaps between joints is also not a primary function of eddy current testing, as this technique focuses primarily on material discontinuities rather than joint separation. The capability to identify both surface and subsurface defects makes this answer the most accurate representation of what eddy current testing can accomplish in practice.