If an indication is detected using direct current, what is the next logical step to determine if it results from a surface or subsurface condition?

When an indication is detected using direct current (DC) in magnetic particle testing, the next logical step to determine whether the indication is caused by a surface or subsurface condition is to inspect the area again using alternating current (AC). This is because the two types of currents produce different magnetic fields that respond differently to flaws.

Direct current creates a more uniform magnetic field, which is very effective for revealing surface-breaking indications. In contrast, alternating current generates a magnetic field that fluctuates, which can penetrate deeper into the material and is more sensitive to subsurface defects. By re-evaluating the indication with AC, you can discern whether the flaw is surface-related or if it extends deeper beneath the surface.

Utilizing a stronger magnetizing force might amplify indications, but it does not specifically differentiate between surface and subsurface defects. Applying more magnetic particles could enhance visibility, yet it does not provide clarity on the nature of the indication. Ignoring the indication altogether would negate the purpose of conducting the test, as it dismisses a potentially critical flaw that may need further investigation. Thus, using alternating current is the most effective method to clarify the nature of the indication.