Which nondestructive testing method is best at identifying near-surface defects in metallic turbine blades, including cracks and coating delaminations?

• A. Ultrasonic testing is best for surface cracks.
• B. Magnetic particle testing is used for turbine blades made of ferrous materials.
• C. Radiography detects only interior cracks.
• D. Eddy current testing detects near-surface cracks and coating delaminations.

Answer: (D)