Which testing method uses AC current to detect small surface flaws?

Eddy current testing is a non-destructive testing method that uses alternating current (AC) to induce eddy currents in conductive materials. When a probe carrying the AC is placed near the surface of the material being tested, it creates a magnetic field that penetrates the material. Any flaws or discontinuities, such as cracks or inclusions, can disrupt the flow of these eddy currents, resulting in measurable changes in the current patterns.

This method is particularly effective for detecting small surface flaws because it is highly sensitive to changes in electrical conductivity and magnetic permeability, making it suitable for assessing the integrity of a variety of conductive materials. The ability to discriminate fine surface defects from the background noise is a key feature of eddy current testing, allowing for precise evaluations of material integrity without causing any damage.

The other methods mentioned serve different purposes: magnetic particle testing is effective for detecting surface and near-surface flaws in ferromagnetic materials using magnetic fields; radiography testing uses radiation to visualize internal structures; and ultrasonic testing employs high-frequency sound waves to find internal anomalies. While all these methods have their specific applications, eddy current testing is uniquely tailored for identifying small surface flaws using AC current, making it the correct choice for this question.