Time to First Maintenance (TFM) for standard galvanized steel in a rural environment is over 100 years. In locations with minimal air pollution, galvanized steel will not need maintenance for a full century or more! And because the Time to First Maintenance Chart is based on data collected since the 1920s, before major improvements in air quality, these longevity estimates for galvanized steel used for construction in the twenty-first century are likely to be conservative.

Since most galvanized structural steel has at least 3.9 to 5 mils of zinc coating, estimated service life in the harshest soil is 35 to 50 years and in the less corrosive soil, 75 years or more. The estimate of service life utilized here is years to complete corrosion of the zinc coating plus an additional time of 25%, to account for partial corrosion of the steel member. This provides the project engineer with information to determine the time to replacement or maintenance for non-critical items such as ground rods and reinforced earth wire to more critical structural components such as pilings, utility poles, and guardrail posts. The American Galvanizer’s Association has compiled corrosion data and service life estimates for hot-dip galvanized steel in soil (Figure 2).

H4 square 15 years, Round 25 years