Interactions between steels and sulphide-producing bacteria—Corrosion of carbon steels and low-alloy steels in natural seawater

Metallic infrastructure immersed in natural seawater is exposed to important corrosion phenomena, which are sometimes characterised by microorganism influenced corrosion. The presence of sulphide-producing bacteria is generally associated with catastrophic cases of material degradation. In this work, commercial steel grades (carbon steels and low-alloy steels) are immersed for approximately 1 year in two types of natural seawater, which contain different concentrations of sulphide-producing bacteria. Gravimetric, microbiological, and electrochemical measurements and corrosion product analyses indicate that in seawater the observed corrosion phenomenon is composed of two different phases. The first phase is characterized by decreased corrosion kinetics correlated with a higher concentration of sessile sulphide-producing bacteria and the formation of sulphur-containing chemical species. The second phase is marked by an increased rate of corrosion. This multidisciplinary study demonstrates the complexity of the interactions between steels and bacteria. The presence of alloying elements in the steel composition affects the rate of corrosion and growth patterns of sessile sulphide-producing bacteria. At the same time, the presence of sulphide-producing bacteria affects in the process of steel corrosion in natural seawater.