Which of the following does NOT influence the depth of penetration in Eddy current testing?

In Eddy current testing, the depth of penetration of the induced currents is significantly influenced by several factors relating to the physical and electrical properties of the test material, as well as the characteristics of the testing setup. The frequency of the alternating current determines how deeply the induced eddy currents can penetrate the material; higher frequencies lead to shallower penetration. The type of material being tested is crucial because different materials have different electrical conductivities and magnetic permeabilities, which affect how eddy currents behave. The diameter of the test coil also plays a role, as a larger coil diameter can spread the magnetic field over a greater depth, thus influencing the penetration.

The color of the material, however, does not affect the interactions of eddy currents with the material itself. While the color can signal certain properties related to surface conditions or corrosion, it does not influence the electromagnetic properties that govern depth of penetration. This makes it the factor that does not have an impact on depth of penetration in Eddy current testing. Understanding these influences is vital for interpreting test results accurately in nondestructive testing applications.