Water travel distance for immersion inspections should be chosen such that the second front reflection does not appear between the first front and back reflections.

• A. Such that the second front reflection does not appear between the first front and back reflections
• B. Exactly 3 inches
• C. Less than 3 inches
• D. Always equal to the thickness of the material being inspected

Answer: (A)

In immersion ultrasonics, the timing of echoes is determined by the travel paths in water and in the material. The near-surface echo (first front reflection) and the far-surface echo (back reflection) create a time window you use to interpret flaws. If a second front reflection—an echo from the front surface after the wave has traveled to the back and returned—lands in between those two primary echoes, it can confuse the back-wall signal. To keep the back reflection clean and interpretable, you choose the water travel distance so that this second front reflection does not appear between the first front and back reflections.

There isn’t a universal fixed distance for this; the appropriate water path depends on material thickness, sound speeds in water and the material, and the transducer frequency. So the correct approach is to set the water path to satisfy that separation criterion, rather than using a fixed distance.