1. Cleaning to Remove Surface Contaminants
Remove rust and oxide scale: Light surface rust (not the stable patina) or loose oxide scale can trap gases, leading to porosity in the weld. Use a wire brush, sandpaper (120–180 grit), or a grinding wheel to clean the area 25–50 mm on either side of the weld joint. Avoid aggressive methods (e.g., heavy sandblasting) that remove the dense, stable patina-only target loose or flaky rust.
Degrease the surface: Oils, greases, or machining fluids on the surface burn during welding, creating gas pockets (porosity) in the weld. Clean the joint area with a solvent like acetone, isopropyl alcohol, or a dedicated metal degreaser. Wipe with a lint-free cloth and allow to dry completely before welding.
Remove paints or coatings: If the steel has temporary protective coatings (e.g., primer, anti-rust paint), strip them from the weld zone using a scraper, wire brush, or paint remover. Residues from coatings can contaminate the weld metal.
2. Handling the Stable Patina
Leave the patina intact outside the weld zone: The patina is critical for the steel's long-term corrosion resistance. Only clean the immediate weld area (as above) to avoid damaging the patina on non-welded surfaces.
Lightly abrade the patina in the weld zone: The patina in the joint area (where welding occurs) should be lightly abraded to expose fresh metal, ensuring good fusion between the base steel and filler material. A wire brush or light grinding (without excessive material removal) is sufficient.
3. Drying to Prevent Hydrogen Induced Cracking (HIC)
If the steel is damp, preheat it to 60–80°C (using a torch or heating blanket) to evaporate moisture before welding. This step is particularly important for plates thicker than 12mm or in humid environments.
4. Edge Preparation for Thick Sections
Use beveled edges (e.g., V-bevel, U-bevel) with a 30–45° angle, leaving a small root face (1–2mm) to prevent burn-through. Clean the beveled surfaces thoroughly to remove burrs or debris.
