A common question in construction and manufacturing is: "Does galvanized steel rust?" The short answer is yes, but much slower than untreated steel. Galvanized steel's zinc coating provides exceptional corrosion protection, significantly extending its lifespan. Let's explore how it works and when rust might occur.
How Galvanized Steel Resists Rust ？
Galvanized steel is carbon steel coated with a protective zinc layer through hot-dip galvanizing or electroplating. This coating offers two defense mechanisms:
The zinc layer physically blocks moisture and oxygen from reaching the steel.
Even small scratches are protected by surrounding zinc.
2. Cathodic Protection
Zinc sacrificially corrodes before the steel (a process called galvanic corrosion).
This buys decades of extra protection versus bare steel.
When Can Galvanized Steel Rust?
While highly durable, galvanized steel can eventually rust under extreme conditions:
Ocean spray accelerates zinc depletion.
Solution: Use higher coating grades (Z275+) or marine-grade alloys.
Deep scratches/cuts exposing bare steel.
Solution: Repair with zinc-rich paint.
Highly acidic (pH <4) or alkaline (pH >12) conditions degrade zinc faster.
Avoid contact with copper/brass (causes rapid galvanic corrosion).
Clean regularly with mild soap to remove corrosive salts/dirt.
Choose the right coating weight:
Z60: Light duty (indoor use)
Z275: Heavy duty (bridges, coastal zones)
Q: How long until galvanized steel rusts underwater?
A: Submerged, it lasts 15-25 years depending on water chemistry.
Q: Does welding galvanized steel make it rust faster?
A: Yes, if uncoated—always grind and repaint weld zones.
Q: Galvanized vs. galvannealed steel rust resistance?
A: Galvannealed (zinc-iron alloy) offers better paint adhesion but similar rust protection.