Angle beam testing of plate will often miss laminations oriented how?

• A. Cracks that are perpendicular to the sound wave
• B. Inclusions that are randomly oriented
• C. Laminations that are parallel to the front surface
• D. A series of small discontinuities

Answer: (C)

Angle beam ultrasonics detect flaws most effectively when there is a boundary that interrupts the wave path at an angle, creating a back-reflected energy returning to the probe. When laminations run parallel to the front surface, their boundaries lie along the surface plane. In this orientation, the wave tends to travel along the laminations with little cross-boundary interaction, so there isn’t a strong reflectivity back to the transducer. The result is that these laminations present a near-smooth interface to the angled beam and are easy to miss during inspection. Other orientations produce more detectable reflections because they present boundaries that intersect the wave path more effectively, but laminations parallel to the surface often evade detection in angle-beam testing.