What inspection method would be most appropriate for checking a nonferrous metal part for intergranular corrosion?

• A. Eddy Current inspection.
• B. Ultrasonic inspection.
• C. X-Ray Inspection.
• D. Dye penetrant.

Answer: (A)

Eddy current testing is well suited for finding intergranular corrosion in nonferrous metals because it focuses on the near-surface region where such corrosion typically affects conductivity along grain boundaries. The technique uses a probe to induce alternating currents in the part; flaws or corrosion along grain boundaries disrupt the flow of these eddy currents, causing a measurable change in impedance. Nonferrous metals conduct electricity, so eddy currents respond strongly to small, surface-adjacent defects, making this method especially sensitive for detecting early or shallow intergranular corrosion without needing to cut into the part or use penetrating radiation.

Dye penetrant relies on surface openings and is effective for surface cracks but may miss subsurface or tightly closed grain-boundary corrosion. Ultrasonic inspection can image internal features but is less sensitive to small, near-surface changes and may require more accessible geometry. X-ray inspection can reveal internal flaws but often lacks the sensitivity for fine grain-boundary corrosion unless it forms distinct features. Eddy current’s combination of surface sensitivity, speed, and suitability for nonferrous materials makes it the most appropriate choice in this scenario.