Identify a steel-sheet surface problem by describing its shape, position and pattern before naming its cause. Keep the observed feature, proposed explanation and unanswered technical question in separate entries. A photograph can support that record; it cannot establish remaining thickness, coating mass or acceptability by itself.
This guide covers surface-imperfection identification. Use the delivery inspection guide for the wider receiving process and the purchase specification guide for agreed requirements.
1. Establish the surface being examined
Record the product, grade, supplied finish or coating, inspected face and processing stage. Compare the affected area with an undamaged area of the same material under similar lighting. A deliberate texture can be mistaken for damage: JFE describes dull and bright cold-rolled finishes produced with different roll surfaces.
Check whether the mark was present before cutting, leveling, forming or coating. If no earlier observation exists, record the stage of discovery without assigning the stage of origin. Identify protective film, oil or loose deposits that may obscure the surface. Preserve the initial condition before any authorized cleaning or sample preparation.
2. Describe the feature, then narrow the possibilities
The following groups guide investigation. Their names do not establish contractual nonconformity; SAE J810 is a classification reference , and the ordered surface requirements still control acceptance.
| Visible feature | Possible family | Useful next observation |
|---|---|---|
| Narrow line or groove | Scratch or mechanical gouge | Direction, ends, displaced metal and whether the feature crosses a coating |
| Similar marks at recurring intervals | Roll-contact impression | Spacing, common width position and whether each mark is raised or depressed |
| Irregular dark patches or small depressions | Scale-related marking or another pit-like feature | Attached residue, surrounding finish and condition after approved examination |
| Partly attached flake or an apparent opening | Scab-like overlap or possible discontinuity | Exact location and extent; retain the feature for specialist examination |
| White, grey or black deposit on zinc-coated sheet | Possible storage stain | Moisture history, distribution and coating assessment |
| Bands first noticed after forming | Possible stretcher-strain marking | Before/after comparison, grade, processing and storage history |
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The source notes distinguish these families. A line can have more than one explanation, and a depression’s appearance does not establish its depth. Describe an uncertain feature plainly rather than forcing it into a defect name.
3. Map repetition and distribution
Record the face, distance from a defined edge, direction relative to rolling, affected length and width, and intervals between repeated features. State how those values were obtained. Include a wider photograph showing location and a close view with a suitable scale; keep the item identifier attached to both.
Repeated impressions justify checking rotating-contact history with the processor. They do not identify a particular machine or responsible party on their own. Isolated marks, continuous tracks and damage confined to an edge require different comparisons. Document the examined area and inaccessible portions; an outer coil wrap gives limited coverage.
4. Separate appearance from material condition
A dark patch, shiny groove or visible deposit answers an appearance question. Depth, remaining section, coating continuity and suitability for the intended finish are separate questions. Ask the responsible technical team to select the measurement or examination needed for the unresolved requirement.
For zinc-coated sheet, consult the galvanized-corrosion explanation without estimating coating loss from colour. For stainless sheet, use the surface-finish guide to establish the supplied appearance. Describe damage to the coating and any suspected opening in the steel separately, even when they share a location.
5. Use an evidence record that survives investigation
Consider two hypothetical observations. A sequence of depressions at similar spacing merits a location-and-spacing record plus a request for process correlation. Calling it transport damage immediately would outrun the evidence. A dark patch revealed after unpacking needs its original condition recorded; the colour alone cannot distinguish residue, scale-related marking and corrosion.
Keep observations, working explanations and confirmed findings in separate fields. Add the relevant order clause or approved sample, the question still open, and the person responsible for resolving it. Do not grind, polish or chemically treat a disputed area merely to improve its appearance. Any agreed preparation should preserve the necessary original evidence and sample identity.
6. Decide against the actual requirement
Compare the verified finding with the specified surface quality, intended use and agreed acceptance method. Record any authorized concession or repair separately. This guide supplies no universal scratch-depth limit, defect-area allowance or sampling rule.
Keep inspection within safe access arrangements. Sharp edges, loose flakes, moving strip and stored coil energy require controlled procedures; do not probe a feature with bare fingers or release bands to improve access. Where a suspected opening, coating failure or unknown depth could affect use, hold the affected material under the site’s approved process until the responsible person determines disposition.