What is the purpose of collecting A-scans at key positions during weld inspection with angle-beam UT?

• A. To count the number of echoes only.
• B. To measure surface roughness.
• C. To capture echoes at specific positions along the weld for sizing and correlation with features.
• D. To change the wedge angle during the run.

Answer: (C)

Collecting A-scans at key positions builds a precise map of reflections along the weld, enabling sizing and locating features accurately. An A-scan shows when echoes from interfaces return; by taking scans at specific spots, you can determine how deep a flaw is (using known material velocity to convert time-of-flight to depth) and estimate its size from the echo amplitude and duration. Mapping these echoes to weld features such as root, toe, and cap lets you correlate indications with exact locations and orientations, which is essential for consistent sizing and documentation. The other options don’t fit because simply counting echoes doesn’t provide size or position; surface roughness isn’t measured this way in angle-beam weld UT; and changing the wedge angle during the run isn’t what creates the reliable position-based map needed for sizing and correlation.