Acoustical lenses are commonly used for contour correction. When scanning the inside of a pipe section by the immersion method, which lens type would be used?

• A. Focused cup
• B. Convex
• C. Concave
• D. Variable pitch

Answer: (B)

Acoustical lenses shape the ultrasound wavefront to match the contour and depth of the inspection area. When scanning the inside of a pipe by immersion, the inner wall is curved, so you want a lens that produces a focused beam at a depth that aligns with that curvature. A convex lens does exactly that by creating a converging, focused beam, which helps maintain the correct incidence and provides better sensitivity to flaws along the curved surface. A concave lens would spread the beam and weaken the inspection at the wall, while a variable pitch lens isn’t specifically aimed at correcting the cylindrical interior geometry, and a focused cup is a different transducer arrangement not ideal for this particular setup.