In which scenario would Eddy Current Testing be ineffective?

Eddy Current Testing (ET) relies on the principle of electromagnetic induction to detect flaws in conductive materials. The technique generates eddy currents that are influenced by the presence of defects in these materials. In the case of non-conductive materials like plastic, eddy currents cannot form because there are no free electrons available to establish the currents needed for the testing process. Therefore, ET is fundamentally ineffective on such materials since it requires a conductive medium to function properly.

In contrast, conductive metals, regardless of defect size, can be tested with ET, as the method is specifically designed for them. Even high conductivity materials can be tested effectively, although adjustments to the testing parameters may be necessary. Thin metallic layers can also be assessed, although special care must be taken due to the possibility of limited eddy current penetration. Thus, the inefficacy of ET on non-conductive materials makes it clear why this is the correct answer.