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Time to First Maintenance

The Time to First Maintenance (Figure 7) for hot-dip galvanized coatings in atmospheric exposure is linear to the zinc coating thickness.  Time to First Maintenance is defined as the time to 5% rusting of the substrate steel.  The minimum average coating thickness requirements outlined in ASTM A123 Table 1 can be used to predict the minimum Time to First Maintenance of galvanized products by material category (structural shapes, strip, plate, pipe, wire, etc). For example, structural shapes that are ¼-thick or greater (other than tubing and plate) are required to have at least 3.9 mils of zinc according to ASTM A123 Table 1.  As the TFM Chart shows, this would equate to 72-73 years of life before maintenance in an industrial environment.

Time to first maintenance chart
Figure 7: Time to First Maintenance Chart for Hot-Dip Galvanized Coatings