Which of the following is a limitation of Eddy current testing?

The correct response highlights the limitation of Eddy current testing, which is its ability to detect subsurface defects. Eddy current testing primarily focuses on surface and near-surface flaws due to the way the technology interacts with the material being tested. The eddy currents generated in conductive materials have a limited penetration depth, generally confined to a few millimeters, depending on factors such as the frequency of the test and the conductivity of the material. This characteristic restricts the method's effectiveness in identifying defects located deeper within the material.

In contrast, other techniques like ultrasonic testing are better suited for detecting subsurface anomalies because they can penetrate deeper into the material. This limitation is significant as it defines the suitability of Eddy current testing for specific applications, particularly where surface integrity is of primary concern rather than deeper structural integrity.

The other options present different considerations: requiring direct contact is necessary for effective data collection, particularly to establish a proper electrical connection with the material; the notion that Eddy current testing can only be used on non-conductive materials is inaccurate since it is specifically designed for conductive materials; and the claim regarding the lack of quantitative data is misleading because, while Eddy current testing might provide qualitative assessments, it can also yield quantitative information under specific conditions with proper calibration and interpretation.