UT Interpretation, Evaluation, and Reporting
Interpretation vs evaluation
Interpretation decides what a signal represents (geometry, weld cap, porosity, crack, lack of fusion). Evaluation compares that against acceptance criteria. Keep them separate-questions often test whether you can distinguish a non-relevant indication (from geometry) from a relevant one (from a flaw).
Signal features that guide interpretation: amplitude, location (depth and surface distance), shape, orientation, and behavior when the probe is moved or rotated. Planar reflectors (cracks, lack of fusion) tend to give sharp, directional responses; volumetric ones (porosity, slag) give broader, less directional echoes. Know how to convert sound path to depth and surface distance using the refracted angle.
Traps
- Calling every echo a defect-geometry and mode-converted signals create non-relevant indications.
- Comparing amplitude without depth correction (DAC).
- Confusing surface distance with sound path.
- Reporting a size without stating the sizing method (6 dB drop, 20 dB drop, tip diffraction).
Worked example
At 45°, sound path 40 mm: depth = 40·cos45° ≈ 28 mm; surface distance = 40·sin45° ≈ 28 mm. Report both, plus amplitude relative to DAC, sizing method, and acceptance reference. A report without method and reference is incomplete.