Experimental Design Considerations for Assessing Atmospheric Corrosion in a Marine Environment: Surrogate C1010 Steel

Abstract

A rigorous assessment of marine atmospheric corrosion at a controlled NRL test site in Key West Florida was conducted. Certain factors which have been previously implicated in the literature as influencing the corrosion of engineering materials in atmospheric exposure were isolated and explored. In particular, the effect of sample size and orientation was explored. Low carbon steel (C1010) witness coupons were exposed in vertical non-sheltered, vertical sheltered, and tilted non-sheltered conditions. The effect of surface area on measured steel mass loss was also explored to identify the veracity of the so-called “edge effect”. Efforts were made to correlate meteorological atmospheric conditions (temperature, relative humidity, wind speed, wind direction, etc.) to the monthly assessment of corrosion damage. Results were assessed in terms of steel mass loss. Additive composite monthly corrosion damage tended to significantly overshoot the observed cumulative corrosion damage for samples exposed over the same period. This observation, among others presented herein, suggests that exposure of samples for less than 6 months is not an adequate predictor of long-term, natural exposure. Additionally, a smaller sample had a larger area-normalized mass loss than a larger sample. The influence of the sample edge (especially the bottom edge) was implicated in causing this difference.

Keywords

• atmospheric corrosion
• mass loss
• edge effect
• corrosivity
• field exposure
• environmental degradation