Evaluating an Indication at a Weld Root with Ambiguous Echo Dynamics
A Level II is inspecting a 20 mm thick carbon steel butt weld. At the root region, a signal appears at 22 mm sound path with a 45-degree probe. The signal amplitude is 80 percent of DAC. When the probe is moved, the signal drops sharply over 3 mm and does not move with the index in the way a planar flaw would. A second angle (60 degrees) shows a signal at a different depth that does not correspond to the same physical location. The weld was made with a ceramic backing tape. The technician wants to call it root lack of penetration.
1. What is the most likely classification of the signal, and why?
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The echo dynamics point away from lack of penetration.
- A sharp drop over 3 mm with little index dependence is characteristic of a geometric reflector or a small volumetric feature, not a planar root flaw. A planar lack of penetration would respond strongly and consistently across a range of indices.
- The 60-degree signal at a non-corresponding depth is consistent with a geometric reflection from the backing tape impression or the root profile, which changes apparent depth with angle.
- Ceramic backing tape leaves a root profile that can produce strong geometric echoes at the root.
Most likely classification: geometric/root-profile signal, not lack of penetration. Confirmation requires a second angle and a comparison with a known root geometry.
2. How would you confirm or refute the classification before reporting?
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Confirmation steps:
- Map the signal across indices and angles. A geometric signal will track the root profile; a true flaw will track a fixed physical location.
- Compare with a reference block that reproduces the backing-tape root profile. If the reference produces the same echo dynamics, the signal is geometric.
- Use a 0-degree longitudinal probe to check the root region for a volumetric feature.
- If accessible, inspect from the other side to see whether the signal is present at the same physical location.
Only after these steps should the signal be classified and reported.
3. What should the report contain, and what is the disposition?
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The report should state: the signal location, amplitude relative to DAC, echo dynamics observed, the angles used, the reference comparison, and the classification with the basis for it.
Disposition: if classified as geometric, the signal is not a flaw and is not reported as a defect, but the basis for that classification must be recorded. If the classification cannot be confirmed, the signal should be reported as an unresolved indication requiring Level III review, not as lack of penetration. The report must not overstate the finding.