Initiation of a corrosion pit in plain carbon steel (CS) was simulated by preconditioning a small area and a larger concentric area as an anode and cathode, respectively. Preconditioning was achieved by applying a galvanic current between the electrodes. During the initial step, the effect of sulfate-reducing bacteria (SRB) on resulting polarization of this artificial galvanic cell was investigated. The previously conditioned electrodes then were left short-circuited, and the naturally flowing galvanic current was measured using a zero-resistance ammeter. This new test procedure was able to replicate the stabilization of a pit and provide direct assessment of the penetration rate inside the pit. SRB were shown to stabilize pitting corrosion of mild steel in synthetic deaerated seawater by maintaining a stable galvanic current between a local anode and a cathode surrounding. In the absence of SRB, the current was negligible. Other bacteria such as V. natriegens may impede stabilization of localized corrosion when using this technique. The presence of SRB was necessary on anode and cathode for stabilization of the galvanic cell. A SRB biofilm considerably affected the potential-current relationship of the concentric electrodes. Under impressed current, there was a depolarization of anode and cathode. In the case of CP, such a depolarization could be detrimental. The present technique explained why localized corrosion may have such an impressive penetration rate in the field although uniform corrosion remains low in standard laboratory experimenters. It was obvious that something more is necessary for really dangerous pitting corrosion from a SRB biofilm. The presently observed penetration rates were still far from the mm/y or cm/y encountered in same fields.
Method for studying stabilization of localized corrosion on carbon steel by sulfate-reducing bacteria
Verfahren zur Untersuchung der Stabilisierung der örtlichen Korrosion an Kohlenstoffstahl durch sulfatreduzierende Bakterien
Corrosion, Houston ; 53 , 6 ; 440-447
1997
8 Seiten, 5 Bilder, 2 Tabellen, 37 Quellen
Article (Journal)
English
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