Galvanizing Lifetime Estimator
Life to first maintenance is proportional to zinc thickness divided by the corrosion rate of the environment. Same 85 µm coating: a rural site may see 100+ years, an offshore splash zone under a decade. This estimator makes that math visible.
Three quick questions
Suggested category: —
Adding paint on top? Duplex systems multiply life 1.5–2.3× →
How the estimate works
The corrosion rate comes from the atmospheric corrosivity category (ISO 9223, as used by ISO 14713-1) — each category carries a band of first-year zinc corrosion rates, which is why the result is always a range, never a single number. The environment, not the coating, is usually the dominant variable: the bar chart above shows the same coating across all six categories.
Worked example
- 85 µm in C3 (urban): about 40 to 100+ years to first maintenance.
- 85 µm in C5 (marine industrial): about 10 to 20 years.
Same coating, an order of magnitude apart — environment dominates. That's also why duplex systems (galvanizing + paint) are specified in aggressive environments: the paint shields the zinc, and the combination outlasts the sum of its parts by a factor of 1.5–2.3.
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Questions
How long does hot-dip galvanizing last?
It depends on coating thickness and environment. Life to first maintenance is roughly zinc thickness ÷ corrosion rate: an 85 µm coating can last beyond 100 years in a rural C2 atmosphere but around a decade in an aggressive C5 marine-industrial one.
What is “first maintenance” for a galvanized coating?
The point at which the zinc coating is substantially consumed and maintenance becomes necessary — not the point of structural failure. ISO 14713-1:2017 advises maintaining before any steel rusting occurs, and preferably while at least 20–30 µm of zinc still remains; in practice maintenance is usually triggered when the coating loses its appearance or becomes degraded.
What are ISO corrosivity categories C1 to CX?
ISO 9223 atmospheric corrosivity classes used by ISO 14713-1: C1 (heated indoor) through C5 (very high) and CX (extreme — offshore, splash zones). Each carries a band of first-year zinc corrosion rates; the tool's environment cards describe them in plain language.
Does galvanizing last longer than the calculator says?
Often yes — first-year rates applied linearly are conservative. Zinc corrosion typically slows after the first years as the protective patina develops.