Long-Term Marine Corrosion Under the Influence of Microbiologically Influenced Corrosion and Calcareous Conditions

Calcareous deposits on and within corrosion products tend to inhibit the (abiotic) corrosion of steels in seawater. Herein, it was considered whether this inhibition effect extends to microbiologically influenced corrosion (MIC) for extended (long-term) exposure periods. Quantitative estimates of corrosion rates were made from reported observations for 46 iron and steel shipwrecks, and other iron and steel objects immersed in seawater at various depths and for extended periods (many around 60 years and some up to 160 years). The observations are correlated with observations of the occurrence of calcareous deposits and information about dissolved inorganic nitrogen (DIN), a critical micronutrient for MIC. The results show that calcareous deposits can inhibit both long-term abiotic corrosion and long-term corrosion influenced by conditions suitable for MIC. The practical implications are briefly reviewed.