THE EFFECT OF SULFATE-REDUCING BACTERIA ON THE ELECTROCHEMICAL-BEHAVIOR OF CORROSION-RESISTANT ALLOYS IN SEA-WATER

Corrosion potential (E(corr)), polarisation resistance (R(p)) and pote ntiodynamic polarisation measurements were conducted on UNS N04400 (Mo nel 400) and UNS N08904(904L) stainless steel in de-aerated sea water in the presence and absence of sulphate-reducing bacteria (SRB). These measurements as well as morphological studies were conducted after di fferent exposure intervals of up to 26 d to the test environment. In t he absence of SRB both alloys were readily passivated. The anodic pola risation behaviour of both alloys was remarkably affected by the prese nce of SRB. Thus exposure of alloy 400 to an SRB environment for 5 hr led to the appearance of an active dissolution peak and prolonged expo sure led to a diminishing of the passive region. The anodic polarisati on curves pertaining to 904L alloy showed a change in behaviour after 14 d where an active/passive transition was recorded and pitting attac k below scattered bacterial colonies was detected. However, under open circuit conditions no pitting was observed. E(corr) for both alloys s hifted in the active direction and R, decreased with the increase of e xposure time to SRB. EDX analysis indicated sulphide-rich layers on al loy 400 which were responsible for the loss of passivity.