Corrosion Protection
Galvanizing, coating, passivating — how to protect metal from rust
AI generated can be stopped in many ways: by material selection, by galvanizing and coating, by cathodic protection, and by clean weld design. The best protection starts before — with the question of how each weld will be protected and where moisture can collect.
Against you have more weapons than just "use stainless steel." Protective measures range from material selection to design — and plays a role in each.
1. Material selection. The most effective protection is to choose a material that suits the environment: structural steel for dry interiors, hot-dip galvanized steel or stainless steel for outdoors, -containing grades for chlorides. You make the choice based on PREN (see article & PREN).
2. Galvanizing. In hot-dip galvanizing, steel is dipped into molten zinc. Zinc is less noble than iron and sacrifices itself first — so it protects not just as a barrier, but cathodically: even if the coating is scratched, the zinc corrodes first, not the steel. That's also why galvanized parts are problematic when : The burns off the zinc, producing toxic zinc fumes, and the weld bead is left unprotected. After , the part must be re-galvanized or the weld protected otherwise.
3. Coating. Paints and powder coatings act as a pure barrier. Their weak point is any scratch — behind it, corrosion continues unchecked. Critical for durability is weld preparation: A clean, smooth, pore-free weld bead accepts the coating better than one with slag and spatter.
4. Cathodic protection. For buried pipelines and ship hulls, the component is deliberately connected to an even less noble "sacrificial metal" (magnesium, zinc, or aluminum anodes). The sacrificial metal corrodes on its behalf.
5. Design for corrosion protection. This is the cheapest and most often forgotten measure — and it starts with :
• No crevices: Overlaps and incomplete penetration welds create traps. Better to weld through than overlap.
• No galvanic corrosion: Do not directly fasten dissimilar metals (steel bolt in aluminum). Prevent by separation or compatible partners.
• Let water drain: No pockets where water can pool. No edges that hold moisture.
• Remove heat tint: After stainless steel, pickle/grind off heat tint and , otherwise the weld will rust despite stainless steel.
The best strategy is always a combination: suitable material + clean weld + thoughtful design. A single measure alone rarely suffices.