Abstract
The marine bacterial strain Desulfovibrio ferrophilus IS5, known for its lithotrophic growth ability to use metallic iron as a sole electron donor and for causing corrosion of steel, was used in the current study. Four commonly used biocides in the oil and gas industry, namely tetrakis(hydroxymethyl) phosphonium sulfate (THPS), glutaraldehyde (GLUT), benzalkonium chloride (BAC), and GLUT/BAC were selected to study their efficacy in controlling carbon steel corrosion in the presence of this strain. Incubations containing strain IS5 and low carbon steel coupons were prepared in the presence and absence of the four biocides, and these were monitored using both electrochemical methods (electrochemical impedance spectroscopy, linear polarization resistance and potentiodynamic polarization) and surface analyses (scanning electron microscopy, confocal measurements, optical microscopy, and profilometry) to assess the biofilm/metal interactions. When THPS, BAC, and GLUT/BAC treatments were applied, minimal corrosion was measured by all methods. In contrast, severe pitting was observed in the presence of 50 ppm GLUT, similar to what was observed when D. ferrophilus IS5 was incubated in the absence of biocide, suggesting that GLUT alone may not be effective in controlling MIC in marine environments. This study also showed that the use of non-destructive electrochemical methods is effective for screening for real time biocide selection and monitoring of the impact of chemicals post-dosage in oil and gas operations.
Highlights
Low carbon (LC) steel is a commonly used material for the fabrication of metal infrastructure in marine offshore oil production applications as it is relatively inexpensive, manufactured, and readily available
In order to study the efficacy of commonly used biocides used in the oil and gas industry, a highly corrosive strain, D. ferrophilus IS5, was selected for performing microbiologically influenced corrosion (MIC) related electrochemical tests over a 15-d incubation period (Fig. 1)
D. ferrophilus IS5 has been previously reported to form a conductive mineral crust on the surface of the metal that showed electrical conductivity[11,15,20]. The formation of such a crust acted as a positive control for optimal growth of D. ferrophilus IS5 in artificial sea water (ASW) medium where no biocide was added during the course of the experiment
Summary
Low carbon (LC) steel is a commonly used material for the fabrication of metal infrastructure in marine offshore oil production applications as it is relatively inexpensive, manufactured, and readily available. SRM able to directly scavenge electrons from a metal surface have been reported to be involved in carbon steel corrosion mechanisms, especially when nutrients are limited[10,11,12,13]. Seawater represents such a nutrient-limited environment where metal like LC steel could be the only potential electron donor source with sulfate present as electron acceptor, allowing for electroactive biofilms to thrive because of the corrosion potential of carbon steel in a marine environment[14]. Amphipathic in nature, surfactants that can penetrate bacterial cell wall and lyse the cells resulting in the loss of osmoregulation capacity
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