Which NDT method uses sound waves to detect internal weld defects?

• A. Ultrasonic testing
• B. Visual inspection
• C. Radiographic testing
• D. Magnetic particle testing

Answer: (B)

Ultrasonic testing uses high-frequency sound waves to inspect the interior of a weld. A transducer sends waves into the metal; when these waves meet internal flaws such as cracks, porosity, or inclusions, part of the energy reflects back to the transducer. By analyzing the timing and strength of the echoes, the inspector can locate and size defects and even measure thickness. This method is particularly useful for welding because it reveals hidden internal conditions that aren’t visible on the surface, without destroying the part. Visual inspection, by contrast, looks only at surface features. Radiographic testing uses X-rays or gamma rays to create an image of the interior, not sound waves. Magnetic particle testing detects surface and near-surface defects in ferromagnetic materials using a magnetic field and dispersed particles.