VT Visual testing (VT)
Visual testing (VT) · Inspección y ensayos · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “VT 100% of welds per ISO 17637 · level B” states a visual testing (vt) requirement.
What controls
Examination carried out with the naked eye or simple optical aids to detect surface defects, discontinuities, apparent geometry and finish condition, checked against a defined acceptance criterion. It is the first non-destructive test in any sequence and, despite its simplicity, it is a formal test: it requires defined lighting, viewing distance and access, and qualified personnel when applied to welds. Whatever is not written down as an acceptance criterion cannot be inspected visually: “good appearance” is not a requirement.
How to verify
Clean, dry surface, adequate lighting, viewing distance and angle within the limits set by the procedure, and aids such as a magnifier, mirror, borescope and gauges. Defects are sized with a gauge or caliper and compared against the applicable acceptance criterion, which is what decides, not the inspector's judgment. What is found, its location and its size are recorded, even if accepted.
Common mistakes when interpreting it
- Treating it as an informal look rather than a test with a procedure, criterion and record.
- Rejecting or accepting on personal impression instead of the applicable acceptance criterion.
- Inspecting without cleaning the surface or without raking light, which is what reveals discontinuities.
How to get it in the workshop / if it comes out of tolerance
Most defects later rejected in expensive tests were already visible here. Use low-angle (raking) lighting so discontinuities cast a shadow, clean the surface before looking and use weld gauges and limit comparators instead of judging from memory. On welds, visual inspection covers size, profile, undercut, craters, spatter and alignment, and all of these have numerical criteria in the applicable quality level.
If inspectors disagree, it is almost always because there is no written criterion or no defined lighting and access conditions. If a visual defect recurs in the same area on every part, it is a process problem, not an inspection problem. And if the surface does not allow viewing (rust, paint, spatter), it must be cleaned first: a visual inspection on a dirty surface is not an inspection.
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