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

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)

Detecting a through-wall crack in a weld with UT relies on using the right inspection angle so the beam interrogates the crack along its plane. A straight-beam setup often can miss a through-thickness crack or show only a back-wall echo that isn’t diagnostic. A single back-wall reflection doesn’t prove a crack and surface roughness isn’t a reliable indicator of internal flaws. By applying an angle-beam UT with the proper wedge, the ultrasonic energy is directed obliquely so it can interact with a through-thickness crack and produce a distinctive angled reflection that travels back to the probe. Seeing that angled indication, and confirming it from multiple probe positions, provides solid evidence of a through-wall crack and helps locate its position and orientation.

Detecting a through-wall crack in a weld with UT relies on using the right inspection angle so the beam interrogates the crack along its plane. A straight-beam setup often can miss a through-thickness crack or show only a back-wall echo that isn’t diagnostic. A single back-wall reflection doesn’t prove a crack and surface roughness isn’t a reliable indicator of internal flaws. By applying an angle-beam UT with the proper wedge, the ultrasonic energy is directed obliquely so it can interact with a through-thickness crack and produce a distinctive angled reflection that travels back to the probe. Seeing that angled indication, and confirming it from multiple probe positions, provides solid evidence of a through-wall crack and helps locate its position and orientation.