Galvanized Steel

Galvanized Steel

Galvanizing is a zinc coating applied to steel, most commonly by hot-dip process — submerging the fabricated piece in molten zinc. The coating functions as sacrificial protection: the zinc corrodes preferentially, protecting the base steel beneath it for as long as the coating remains intact. It is a protective system, not a surface finish.

Failure mechanism

Galvanized coatings degrade gradually and predictably. The zinc layer thins over years of exposure as it sacrifices itself in place of the steel underneath. The relevant indicator is color: a shift from dull white/grey oxidation (zinc still active) to red-orange rust (zinc consumed, base steel now corroding directly). That color transition marks the point at which protection has ended — it is a functional change, not a cosmetic one.

Repair requirements

Welding galvanized steel without first addressing the coating is a safety hazard, not a technique preference. Heating zinc generates toxic fumes requiring proper ventilation and ash preparation. Independent of the safety issue, welding through an unaddressed coating also compromises the weld itself. Correct repair procedure removes the coating at the weld zone, completes the weld, and re-protects the affected area afterward using cold-galvanizing compound or an equivalent coating matched to the piece's exposure conditions.

Repair, recoat, or replace

Isolated red rust on an otherwise sound structure typically indicates a spot-repair or recoat scope. Widespread coating failure across a piece nearing the end of its service life typically indicates a replacement decision — recoating a structure failing broadly delays the underlying issue rather than resolving it.