Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

At this depth, wave energy is about 4% of the wave energy at the surface,
and the amplitude of oscillation decreases sharply to a negligible value at
greater depths. Surface waves follow contoured surfaces. For example,
surface waves traveling on the top surface of a metal block are reflected from
a sharp edge, but if the edge is rounded off, the waves continue down the
side face and are reflected at the lower edge, returning to the sending point.
Surface waves will travel completely around a cube if all edges of the cube
are rounded off. Surface waves can be used to inspect parts that have
complex contours.