1. Never Damage the Protective Rust Layer (Core Rule)
Prohibit harsh cleaning: Skip wire brushes, sandblasting, grinding, or acidic/alkaline cleaners. These strip away the dense outer rust, exposing the bare steel and forcing it to restart rusting (which weakens long-term protection).
Gentle cleaning only: If you notice loose, flaky rust (common in the first 6–12 months) or surface dust, use a soft nylon brush or low-pressure water (≤30 bar, like a standard garden hose) to wipe/rinse it off. This keeps the layer clean without harming its structure.
2. Support Rust Layer Maturation (Critical for the First 24 Months)
Ensure natural dry-wet cycles: Q235NH needs regular exposure to rain and sunlight (not permanent shelter or standing water). Wet conditions trigger rusting, while dry periods help convert loose rust (FeO(OH)) into the dense, protective α-FeO(OH). If water pools on the steel (e.g., at component joints), drill small drainage holes to prevent "over-rusting" in that area.
Clean dust and pollutants regularly: Every 1–3 months, rinse the surface with clean, low-pressure water. Dust, oil, or industrial grime (like sulfur deposits near factories) can block the steel's contact with air, causing uneven rusting or pitting. For sticky oil stains, use a mild, neutral detergent (pH 6–8) to gently wipe the area, then rinse thoroughly-never use abrasive cleaners.
3. Prevent Harm from Incompatible Materials
Avoid direct contact with plain carbon steel: Never attach Q235NH to ordinary steel (e.g., Q235B) using uncoated bolts or brackets. Plain carbon steel rusts faster and produces loose rust that contaminates Q235NH's patina, leading to "galvanic corrosion" (speeding up local rusting on Q235NH).
Use compatible fasteners: If you need to connect Q235NH to other parts, use stainless steel (e.g., 304) bolts and add an insulating gasket (e.g., EPDM rubber) between the two metals. This blocks cross-contamination and preserves the rust layer.
4. Simple Upkeep for Mature Rust Layers (After 24 Months)
Protect from physical damage: Avoid scraping or hitting the layer with hard tools (e.g., construction equipment). If small scratches occur (≤5mm), leave them-Q235NH will re-rust and repair the scratch naturally in 1–3 months (faster in humid areas).
Clean only when needed: In clean, inland areas, rinse with low-pressure water every 6–12 months. In dusty or coastal areas (with salt spray), clean every 2–4 months to wash away salt or dirt that could break down the layer.
