Abstract
Various cases of accidents involving microbiology influenced corrosion (MIC) were reported by the oil and gas industry. Sulfate reducing bacteria (SRB) have always been linked to MIC mechanisms as one of the major causes of localized corrosion problems. In this study, SRB colonies were isolated from the soil in suspected areas near the natural gas transmission pipeline in Malaysia. The effects of ATCC 7757 and consortium of isolated SRB upon corrosion on API 5L X-70 carbon steel coupon were investigated using a weight loss method, an open circuit potential method (OCP), and a potentiodynamic polarization curves method in anaerobic conditions. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were then used to determine the corrosion morphology in verifying the SRB activity and corrosion products formation. Results from the study show that the corrosion rate (CR) of weight loss method for the isolated SRB is recorded as 0.2017 mm/yr compared to 0.2530 mm/yr for ATCC 7757. The Tafel plot recorded the corrosion rate of 0.3290 mm/yr for Sg. Ular SRB and 0.2500 mm/yr forDesulfovibrio vulgaris. The results showed that the consortia of isolated SRB were of comparable effects and features with the single ATCC 7757 strain.
Highlights
Deterioration of metal by corrosion processes directly or indirectly involving microorganisms has gained enormous attention recently
The first bacteria strain was sourced from the American Type Culture Collection with reference number ATCC 7757 while the second sulfate-reducing bacteria (SRB) strain was obtained by a simple isolation technique from soil/mud near the natural gas pipeline in Peninsular Malaysia during pipe maintenance work
After all selective mix-cultures were isolated, only 2 samples showed the presence of SRB while no sample indicated the presence of iron reducing bacteria
Summary
Deterioration of metal by corrosion processes directly or indirectly involving microorganisms has gained enormous attention recently. The most highlighted accidents likely involving MIC as the culprit are the Carlsbad, New Mexico, natural gas pipeline explosion [5] and the 2006 Alaska pipeline leak [6]. These devastated accidents have caused turmoil in the global oil market [6]. Sulfate-reducing bacteria (SRB) were the prime suspect for the accident in Alaska, proving how severe the corrosion can progress under microbial activity influence. Recent studies by Venzlaff et al [8] and Enning et al [9] have shown that corrosive SRB indicated direct consumption of iron-derived electrons rather than H2 as a crucial mechanism
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