Back gouging exposes a root region for further welding. The surface may still contain an original discontinuity, gouging residue or an unsuitable shape for the next pass. Once covered, that intermediate condition is harder to assess. [1]
Mark the gouged length and its relationship to the weld ID. Record excavation depth, remaining section and the preparation required by the qualified procedure. A bright-looking surface is not by itself proof that every original flaw was removed.
Use an intermediate inspection gate
| Feature | Evidence before welding | Why timing matters |
|---|---|---|
| Original defect | Mapped location and relevant surface examination | Must be resolved before burial |
| Residue or contamination | Approved cleaning/preparation evidence | Can affect the next fusion boundary |
| Excavation shape | Access, profile and remaining material | Controls next-pass reach |
| Surface damage | Method suitable for material and geometry | Potential new discontinuities introduced during preparation |
Match inspection to the expected feature
Visual examination gives surface and geometry evidence. A further surface method may be needed under the approved plan to resolve cracks or other indications. Its residues and cleaning requirements also belong in the oil-wetted manufacturing boundary.
A narrow groove can limit both probe access and welding access. The preparation should be reviewed against the qualified joint rather than accepted because its deepest point reaches the original root.
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]
Reconcile gouged depth with the next joint state
Assumptions: the joint is 6.0 mm thick; a mapped root crack extends 2.5 ± 0.2 mm from the original surface, with the interval treated as a depth bound. Gouging to 2.0 mm leaves a 4.0 mm geometric ligament, but the crack can still extend 0.3–0.7 mm below the new surface. Hold the next weld and resolve the remaining indication. A proposed 3.0 mm excavation would clear that bounded depth by at least 0.3 mm but leave only 3.0 mm ligament; both its remaining section and next-pass geometry need the approved repair basis and actual exposed-surface examination. A deposited bead cannot retrospectively prove that the buried crack was removed.
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.