What inspection method effectively identifies subsurface defects in metallic structures?

Eddy current inspection is an effective method for identifying subsurface defects in metallic structures due to its ability to detect variations in material conductivity and magnetic permeability. This technique utilizes electromagnetic induction to generate eddy currents in the test material. When a flaw such as a crack or a void exists beneath the surface of the material, it disrupts the flow of these currents. The changes in the eddy current response are then measured, which allows for the detection of subsurface anomalies that may not be visible through surface inspection methods.

Visual inspection, while useful for surface defects, does not penetrate the surface and therefore cannot identify subsurface issues. Dye-penetrant inspection is primarily effective for surface defects and relies on the ability of a dye to seep into cracks and reveal them, but it too is not effective for subsurface defects. Magnetic particle inspection identifies surface and near-surface defects by using magnetic fields and iron particles but, similar to the others, is limited to shallow flaws. All of these methods have their specific applications, but for detecting subsurface flaws within metallic structures, eddy current inspection stands out as the most effective choice.