Hot-Dip Galvanizing in Atmosphere Time to First Maintenance

The chart below is a plot of the data accumulated from galvanized steel samples performance in real-world applications. The data was generated from the Zinc Coating Life Predictor, which performs calculation based on models developed using statistical methods, neural network technology, and an extensive corrosion database.

The time to first maintenance is linear and directly related to the zinc coating thickness.

The Time to First Maintenance Chart shows steel components greater than 1/4-inch thick will be maintenance-free for more than 70 years in an industrial environment. As stated before, the data from the chart is based on hot-dip galvanized steels actual performance in the field. Do not be confused by manufacturers of other corrosion protection systems who claim their products perform as well as hot-dip galvanizing in accelerated testing, namely salt spray tests.

Salt spray tests do not allow zinc to go through the normal wet and dry cycles, which are crucial to the development of the zinc patina (a key component to galvanizings longevity). Thus, they do not accurately represent the durability of hot-dip galvanized coatings or any zinc coatings, for that matter.

The corrosion rates of zinc have decreased over the past 30 years due to environmental policies and industrial improvements that have resulted in a cleaner environment. Restrictions on the exhaustion of harmful chemicals and improvements in fume capture and exhaust air controls, as well as fuel changes, have significantly improved air quality and reduced pollution levels. By reducing pollution levels – or corrosive elements in the air – the corrosion rate of metals, particularly zinc, also decreased.

Time to first maintenance is defined as the life until 5% of the substrate surface is showing iron oxide (rust). At this stage, it is unlikely the underlying steel or iron has been weakened or the integrity of the structures protected by the galvanized coating is otherwise compromised by corrosion. An appropriately selected corrosion protection system such as zinc-rich paint, zinc metal spray, or zinc solder may be used to repair the exposed area.

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