A tank corner can restrict electrode access to one fusion face. Its outer bead may be smooth while a hidden interface remains incompletely fused. The inspection plan needs to reach that interface with a method demonstrated for the geometry. [1]
Draw the joint preparation and expected fusion surfaces in section. Include real plate thickness, root position, access and the completed tank surfaces available for inspection. Compare the section with the qualified welding procedure.
Map the interface to the evidence
| Evidence route | Question answered | Blind boundary |
|---|---|---|
| Visual examination | Surface profile and accessible defects | Hidden fusion face |
| Ultrasonic method | Response from a favorable discontinuity orientation | Geometry, thin section and beam access |
| Radiographic method | Projected internal contrast | Planar orientation and superposed thickness |
| Representative section | Actual fusion on the sampled plane | Untested length and production variation |
Check the process mechanism without guessing a cure
Fit-up, angle, access and thermal conditions can affect fusion. The thin and thick members may remove heat differently. Review the actual procedure and production evidence rather than prescribing more current as a universal correction; that can create other defects.
A representative section should match the joint and relevant production conditions. It is valuable process evidence, but one good section does not prove every metre of a final seam.
Choose NDT using material, weld thickness, welding process, quality requirements and demonstrated coverage. NDT acceptance levels are not a detailed one-to-one translation of weld quality levels. [2]
Test access to the hidden fusion face
Assume a representative corner mock-up demonstrates detection over 18 mm of a 25 mm target interface. Demonstrated coverage is 72%, leaving 7 mm unresolved. Choose complementary inspection or fabrication evidence that addresses that face under the accepted plan; a smooth outer bead does not close the gap.
References
- U.S. Federal Highway Administration, Bridge Welding Reference Manual, FHWA-HIF-19-088, 2019.
- ISO, ISO 17635:2025, Non-destructive testing of welds — General rules for metallic materials.