1. Why the normal rust layer (patina) does not fall off
This layer has strong adhesion to the base metal, like a "protective film" that blocks further contact between the steel and external corrosive media.
The patina is hard and compact, with no obvious gaps or looseness, so it will not fall off due to wind, rain, or slight external friction during long-term use.
2. Circumstances that may cause the rust layer to fall off
Abnormal patina formation in harsh environments: In areas with excessive salt spray (e.g., coastal areas within 1km of the sea) or high concentrations of industrial pollutants (e.g., heavy chemical zones), the oxidation rate of Corten B is too fast. The rust layer may grow unevenly, forming loose, powdery rust (instead of a dense patina) that easily falls off when washed by rain or blown by wind.
Mechanical damage to the surface: If the Corten B surface is hit by hard objects (e.g., construction collisions, gravel impact), or rubbed vigorously (e.g., improper cleaning with steel wool), the formed patina may be scraped off or cracked, and the newly exposed bare steel will generate loose rust that is easy to fall off before a new stable patina is formed.
Surface contamination during initial use: If the Corten B surface is contaminated with oil, grease, or dust during installation or storage, the oxidation reaction will be blocked. The rust layer will grow locally and unevenly, and the contaminated parts may form loose rust that falls off.
3. How to avoid the rust layer from falling off
Ensure the surface is clean before use: Remove oil, dust, or protective film residues to allow uniform oxidation of the steel surface.
Avoid excessive mechanical impact: Take protective measures (e.g., covering with cushions) during transportation and installation to prevent surface scratches.
For harsh environments (e.g., heavy salt spray areas), pre-treat the surface (e.g., spray a weathering steel primer) to guide the formation of a stable patina and reduce the risk of loose rust.
