Large grains in a metallic test specimen usually result in which effects?

• A. Decrease in back surface reflection
• B. All of the above
• C. Decrease in penetration
• D. Large hash or noise indications

Answer: (B)

Coarse grain structures in metal scatter ultrasonic energy more than fine grains, and this scattering comes with higher attenuation as the wave travels. That increased scattering means less energy returns from the back surface, so the back-wall reflection is weaker or distorted. Attenuation also limits how deep the ultrasound can effectively probe, reducing penetration and making deeper features harder to detect. The random scattering at grain boundaries creates grain noise or hash in the signal, which appears as a noisy, textured indication on the display. Because these effects occur together, the best description is that all of the above happen with large grains.