1. Pre-Welding Preparation: Eliminate Patina Interference (Most Critical Step)
Define the cleaning range: Remove patina from a 20–50 mm wide area on both sides of the weld joint (including groove surfaces if beveled). This ensures the welding electrode directly contacts the clean steel substrate.
Select cleaning methods based on patina thickness
Post-cleaning protection: Complete welding within 4–8 hours after cleaning to avoid new light rust formation. If delayed, cover the cleaned area with anti-rust film (remove before welding).
Clean non-welding areas: Wipe the rest of the plate surface with a dry cloth to remove dust/oil-prevent contaminants from splashing into the weld pool during welding.
2. Welding Process Control: Match Materials & Optimize Parameters
Use weathering steel-specific welding materials
Choose electrodes/wires with the same alloy composition (Cu, Cr, Ni) as the base steel to ensure the weld zone has equivalent corrosion resistance:
Manual arc welding: E7018-C1, E8018-W electrodes.
Gas metal arc welding (GMAW): ER80S-G, ER110S-G wires.
Avoid generic carbon steel welding materials-they will reduce the weld's weathering performance.
Optimize welding parameters
Heat input: Use low-to-moderate heat input (15–25 kJ/cm) to minimize oxidation of the weld pool and avoid damaging the patina in non-welding areas.
Arc length: Keep the arc short (2–3 mm) to reduce air contact with the molten metal and lower porosity risks.
Welding speed: Maintain a stable speed (10–15 cm/min) - slow speed causes overheating, fast speed leads to incomplete fusion.
Shielding gas (for GMAW): Use a mixture of 80% Ar + 20% CO₂ to protect the weld pool from atmospheric contamination.
Avoid welding defects during operation
Ensure full penetration of the weld joint; avoid gaps between the base plates.
Remove slag between welding passes to prevent slag inclusions.
3. Post-Welding Treatment: Restore Aesthetics & Corrosion Resistance
Grind the weld seam: Use an angle grinder to smooth the weld bead and remove spatter-ensure the weld surface is flush with the base plate to avoid water accumulation (a source of corrosion).
Restore uniform patina on the weld zone
Clean the ground weld area with acetone to remove oil residues.
Apply a weathering steel-specific patina accelerator evenly on the weld seam and adjacent areas.
Maintain 70–90% humidity for 2–3 days to promote patina formation-this makes the weld zone's color match the surrounding base steel.
Seal for harsh environments: For plates used in coastal/industrial areas, apply a transparent breathable fluorocarbon sealant over the entire plate (including the weld) after patina maturation. Reapply every 1–2 years to enhance corrosion resistance.
4. Post-Welding Inspection: Verify Welding Quality
Visual inspection: Check for surface defects (porosity, cracks, incomplete fusion)-reject plates with visible defects.
Non-destructive testing (NDT): For structural applications, use ultrasonic testing (UT) or radiographic testing (RT) to detect internal weld defects.
Corrosion resistance test (optional): Conduct a 200-hour salt spray test on the weld zone-qualified welds will form a uniform patina with no pitting corrosion.
