Corrosion of vertical steel strips exposed in the marine tidal zone and implications for ALWC

Accelerated Low Water Corrosion (ALWC) particularly of steel sheet piling in harbors has been documented in various parts of the world. It is thought to involve microbiological influences but the precise mechanisms involved remain to be explained. This paper reports in-situ field investigations for the corrosion of long lengths of mild steel strips exposed at 10 locations on the Eastern Australian seaboard for up to 3 years. Preliminary results show that corrosion below the mean low water level was more severe for higher average concentrations of total nitrogen concentration in the bulk seawater. This is consistent with earlier findings that elevated nitrogen levels increase corrosion, an observation earlier attributed to microbiological influences. The results presented allow the prediction of the likelihood of the occurrence of long-term ALWC through short-term corrosion profile experiments or when measurements are available of bulk water nutrient concentration. It is proposed that the influence of bacteria also holds for freshwater conditions although the rate controlling nutrients are likely to be different.