Monitoring of the Water Quality of Anaerobic Sea Water Using Large-sized Steel Tank

Research on Corrosion of Structural Steelwork in the Anaerobic Sea Water Containing Sulfides (Part 1)

Abstract

The water quality change under an anaerobic condition was examined in the 30m³ steel tank. Measuring items were the concentrations of dissolved oxygen (DO), of total sulfides, of ferrous ion, the number of sulfate reducing bacteria (SRB), redox potential (ORP), and pH. The measurement was started from January, and its period was 394 days.
DO decreased to 0ppm in about a half year. At this moment, the SRB started to be detected. Sulfides concentration increased rapidly, reaching 1.38ppm. It fell to 0.03ppm from January to March. The strong correlation was obtained between log. of total sulfides concentration and ORP. The correlation coefficient was -0.88. It was shown that ORP were near to equilibrium redox potentials (S/H₂S), (FeS₂/FeS, H₂S), (S/HS^-). The ferrous iron was dissolved through epoxy coating.
It can be expected that these results are useful to elucidate the corrosion mechanism and to develop its protection technology.