How pickling affects the corrosion resistance of weathering steel plates is a dual-edged outcome, which is largely determined by whether the pickling process is strictly controlled and whether standardized post-treatment is implemented in a timely manner.
Negative Impacts on Corrosion Resistance Without Proper Post-Treatment
Weathering steel derives its core corrosion resistance from a dense, self-healing patina layer, which is formed by the enrichment of alloy elements (Cu, Cr, Ni, P) on the surface. Pickling, which uses acidic solutions to dissolve surface oxide scales, inevitably erodes the outermost layer of the steel where these corrosion-resistant alloy elements are concentrated. This directly disrupts the foundation for rapid patina formation. After pickling, the exposed fresh steel substrate is highly reactive and vulnerable to flash rust in humid environments. Unlike the protective patina, this flash rust is loose and porous, failing to block the penetration of oxygen and moisture. As a result, the short-term corrosion resistance of the weathering steel plate is significantly reduced-localized pitting corrosion may even occur if the surface is left unprotected for more than 24 hours in high-humidity conditions.
Controllable Impacts With Standardized Process and Timely Post-Treatment
When pickling is performed under strict process parameters (using 5–10% dilute hydrochloric acid or 8–12% phosphoric acid, controlling the temperature at 20–30°C, and limiting the pickling time to 10–20 minutes to avoid over-corrosion), it only removes the loose oxide scales without excessively dissolving the internal alloy elements of the steel substrate. The key to restoring corrosion resistance lies in
immediate post-treatment within 1–6 hours after pickling and drying:
For plates intended for natural patina use: Applying a weathering steel-specific rust stabilizer or patina accelerator can accelerate the migration of residual alloy elements to the surface, promoting the formation of a dense protective patina within 2–4 weeks. At this point, the corrosion resistance of the pickled plate can be fully restored to the level of the original unprocessed steel plate.
For plates requiring coating: Applying a compatible primer (e.g., epoxy zinc-rich primer) promptly forms a continuous protective film on the pickled surface, which blocks the contact between the steel substrate and the external corrosive medium. This not only maintains long-term corrosion resistance but also improves the adhesion between the coating and the steel surface, enhancing the durability of the coating system.
