1. Main Causes of Surface Bubbles
(1) Manufacturing Defects
Rolling Process Issues:
If bubbles appear right after production, they may result from trapped gas (hydrogen/nitrogen) during continuous casting or hot rolling.
Poor slab quality or improper rolling temperature can cause subsurface blisters that later surface.
(2) Corrosion-Related Bubbles
Early Rusting Stage:
Weathering steel forms a protective patina, but in high-humidity or chloride-rich environments (e.g., coastal areas), localized corrosion under the oxide layer can generate H₂ gas bubbles.
This is common if the steel is exposed to saltwater or industrial pollutants before the patina stabilizes.
(3) Coating/Contamination
Oil or Residue:
Residual rolling oil or dirt on the surface may trap moisture, causing pitting corrosion that appears as bubbles.
2. Solutions & Prevention
| Scenario | Action |
|---|---|
| Freshly Delivered Steel | Demand mill test reports (MTC) to check for hydrogen embrittlement or rolling defects. Reject defective batches. |
| In-Service Corrosion | - Ensure proper drainage to avoid water pooling. - Clean surfaces regularly to remove chlorides/dirt. - Accelerate patina formation with weathering accelerants (e.g., copper sulfate solutions). |
| Contamination | Degrease with alkaline cleaners before installation. |
3. Technical Notes
SPA-H's Patina Process:
The steel's rust layer should stabilize into a dense, adhesive oxide (not flaky or bubbled). Bubbles suggest unstable corrosion, often due to:
High chloride/sulfur exposure.
Lack of wet/dry cycling (needed for patina formation).
