How would you detect a through-wall crack in a weld using UT?

• A. Use a straight-beam UT with a flat plate; look for normal reflections.
• B. Use a pulse-echo straight-beam UT and interpret a single back-wall echo for crack.
• C. Use angle-beam UT with an appropriate wedge and look for characteristic angled reflections that indicate a through-thickness crack, corroborated by multiple positions.
• D. Rely on surface roughness to indicate cracks.

Answer: (C)