Microbial corrosion is a serious problem in the petroleum industry. The corrosion of offshore structures, ships, pipes and electric systems is the main source of operational problems and economic loss. Several factors affect biofilm formation in metal surfaces.

This work evaluates the influence of chromium concentration, as a steel alloy component, both on biofilm formation and on corrosion rates. Three steel alloys, 0.03, 1 and 13% chromium, were studied.

A circulation looping system made of PVC tubes was used. Metal probes and electrodes, for electrochemical monitoring, were fixed to this system. After 15 days, the microorganisms present in the biofilm were quantified and the corrosion rates evaluated. The results showed a greater microorganism concentration on alloys with 0.03% chromium. The increase of the amount of chromium in metals alloys led to smaller microorganism concentration on biofilms, and consequently on the corrosion rates.

Analysis of the corrosion rate and galvanic current by electrochemical monitoring showed that the higher chromium concentration caused a smaller corrosion rate.
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