A comprehensive corrosion study was conducted over a period of twelve months at three exposure sites along the Florida coast: Daytona Beach, Kennedy Space Center (KSC), and the US Naval Research Laboratory, Key West. The long-term goal was to develop a better method to categorize the environmental severity of the exposure sites in terms of corrosion attack, which will aid in the design of accelerated laboratory testing and lifetime prediction for bare metal substrates in coastal environments. Measurements included site-specific weather parameters, mass loss of 1018 steel, and pitting characteristics of uncoated aluminum alloy (AA) 7075-T6. The results of this study yielded an overall ranking in severity of the three sites in terms of corrosion behavior for both steel and aluminum: KSC was the most severe, followed by Daytona Beach, which was slightly more severe than Key West. Pitting characteristics of the steel and aluminum substrates exhibited a strong positive correlation to cumulative salt deposition, but not to other weather parameters, such as exposure to various levels of relative humidity for various lengths of time. For AA7075-T6, lateral pit growth dominates over depth penetration, making mass loss determinations problematic and unreliable, whereas mass loss data for the 1018 steel provided clear indication of the increase in corrosion rate over time at the three exposure sites. However, analysis of the pitting on AA7075-T6 in terms of cross-sectional area and volume loss indicate a logarithmic increase over time for the three sites. These results reinforce the conclusion that while mass loss of steel coupon can be used as indicators of corrosion severity, mass loss for 7075-T6 aluminum alloy is an unreliable parameter to use for determining corrosion severity in the field.
The corrosion severity of an environment is important for both design and maintenance of infrastructure especially in marine and costal environments. Corrosion can vary drastically depending on conditions such as temperature, humidity, salt loading, and rain events.1 The interplay between these variables is quite complex so a variety of indirect techniques for quantifying corrosion severity are typically used. One common method is the determination of corrosion rate by measuring the mass loss of steel coupons exposed in the field.1 Measuring the change in mass of the steel coupon as a result of the corrosion product being removed from the substrate can provide the rate of corrosion after a specific exposure time in the field.2