ET ASNT Level II Practice Exam

As the thickness of a conductive material increases, the eddy current flow typically decreases. This phenomenon can be attributed to the skin effect, which describes how alternating currents (including those responsible for generating eddy currents) tend to flow closer to the surface of a conductor rather than uniformly throughout its volume. At higher frequencies, eddy currents are concentrated in a thinner layer called the skin depth. As the material's thickness exceeds this skin depth, a smaller proportion of the total cross-section conducts the eddy current, resulting in a decrease in the overall eddy current flow. Thus, thicker materials tend to suppress the intensity of these currents because they restrict the effective area in which they can circulate, further leading to a reduction in their magnitude.