Abstract
Often the most severe maritime environmental degradation for ships occurs just above the waterline within the splash zone where periodic wet-dry cycles accelerate corrosion. Similarly, increased corrosion also occurs at coastal areas where nearby wave action generates more sea-spray aerosols. These areas are subjected to typical degradation through atmospheric deposition and stressors such as UV light but also have an increased time of wetness (ToW) and higher chloride deposition rate compared to atmospheric exposure alone. It has been seen previously that elevated ToW and chloride loading are correlated to higher corrosion rates of various materials.
The objective of this work was to compare the effect on corrosion of different field exposure conditions: atmospheric exposure in a medium chloride environment, atmospheric exposure with periodic seawater spray, cyclic alternate immersion, and a typical accelerated atmospheric testing protocol (GM 9540). Test materials included copper alloy, silver, and carbon steel. Oxide analysis was performed using coulometric reduction and used in conjunction with microscopy, glow discharge optical emission spectrometery and x-ray diffraction to determine the type of surface films present, the presence of specific species and film thickness for the exposed materials. In addition to a comparison of different exposure methods, a time-resolved comparison between atmospheric exposure and atmospheric exposure with the addition of seawater spray was made.
