Transition from Marine Immersion to Coastal Atmospheric Corrosion for Structural Steels

Field data for the corrosion of structural steel in the tidal and near-shore marine atmospheric zones taken from a variety of sources are reexamined and then interpreted in the light of a phenomenological model recently proposed for marine immersion corrosion loss. That model predicts a relatively short initial period followed by oxidation as the governing corrosion process. Eventually, this is overtaken by anaerobic corrosion. The data trends for tidal and atmospheric corrosion show a surprising degree of consistency with the model, suggesting that longer-term marine atmospheric corrosion involves some degree of participation of anaerobic corrosion processes. This conclusion is supported by the gradual transition from immersion through tidal to atmospheric corrosion behavior evident in the data available in the literature. It also casts doubt on the validity of the power law c = At^B widely used in the corrosion literature for describing corrosion loss as a function of time and for extrapolating to long-term corrosion estimates from short-term observations. Moreover, a preliminary analysis shows that the time of the transition from aerobic to anaerobic corrosion is a nonlinear function of mean atmospheric temperature as a surrogate for metal surface temperature.