Resolving a Disputed Indication on a Pressure-Vessel Weld Under Poor Illumination
A Level II inspector reports a linear indication about 6 mm long on a 12 mm fillet weld joining a nozzle to a shell. The work is performed in a fabrication shop at 07:00 with ambient illumination measured at 150 lx at the weld surface. The inspector used a white-light flashlight (claimed 900 lx at 300 mm) held roughly 200 mm from the surface at a low grazing angle, and a magnifying glass of unknown diopter. The indication appears as a faint dark line parallel to the weld toe. Surface condition is as-ground with visible grinding marks running perpendicular to the suspected indication. The Level III is asked to accept or reject the call before the weld is released for hydrotest. No penetrant or magnetic particle testing has been performed.
1. Evaluate whether the reported indication was observed under conditions adequate to support a valid visual testing call, citing the illumination and equipment factors that matter.
Read the worked answer
The call is not yet defensible. Three factors must be checked:
- Illumination at the surface, not at the lamp. The relevant quantity is the illuminance at the inspection surface, not the lamp's rated output. A flashlight rated 900 lx at 300 mm, held at 200 mm, is not delivering a verified value - inverse-square behavior and beam non-uniformity mean the actual surface value is unknown. The measured 150 lx ambient is below what is normally required for detecting fine indications on a as-ground weld; typical practice calls for substantially higher surface illuminance for critical weld examination.
- Contrast and angle. A faint dark line parallel to the toe, viewed at low grazing angle, can be a true geometric shadow (toe undercut, mismatch) rather than a discontinuity. Grazing light enhances surface relief but also amplifies shadowing artifacts.
- Magnifier. A magnifier of unknown diopter cannot be assumed to provide the required angular resolution; magnification must be known and appropriate, and the working distance must be short enough to actually resolve a 6 mm feature.
Conclusion: the observation is inconclusive as performed. The Level III should require re-examination under controlled, measured illuminance at the surface, with a known magnifier and documented viewing distance, before accepting or rejecting the indication.
2. The grinding marks run perpendicular to the suspected indication. Explain how this surface texture interacts with the observation and what re-preparation you would direct.
Read the worked answer
Perpendicular grinding produces a series of parallel ridges and valleys. A linear indication running parallel to the weld toe but perpendicular to the grind marks means the grind pattern crosses the indication at roughly 90°. This has two effects:
- Masking: the grind valleys create their own dark linear shadows that can mimic or obscure a true linear discontinuity, especially under grazing light.
- False-positive risk: the eye tends to connect collinear dark segments; a grind valley aligned with the viewing direction can read as a crack-like line.
Direction: lightly re-prepare the suspect zone (blend the grind pattern locally, e.g., with a fine abrasive followed by cleaning) so the surface texture no longer runs across the indication, then re-examine under controlled illumination from at least two viewing angles. If the line persists after the texture is removed, it is a candidate discontinuity and should be characterized by a volumetric or surface method (MT/PT) rather than resolved by VT alone.
3. State the decision you would record and the basis for releasing or holding the weld for hydrotest.
Read the worked answer
Record the finding as indication reported, not yet characterized - hold. The basis:
- VT alone, under unverified illumination and unknown magnification, cannot establish whether the feature is a crack, toe undercut, or a grinding artifact.
- The feature is linear and oriented parallel to the toe - a location where lack of fusion and toe cracks are plausible, so it cannot be dismissed.
- Release for hydrotest requires either (a) re-examination under controlled conditions showing the feature is a benign surface artifact, or (b) surface method (MT or PT) characterization consistent with the applicable acceptance criteria.
Document: measured illuminance at surface, magnifier power, viewing distance and angle, surface preparation, and the re-examination result. Do not release on the strength of the original observation.