They were purified and will be sent out for identification. Bacterial strains of interest were used in antimicrobial screenings and test loop experiments. Parameters for the laboratory-scale test loop system such as gas and culture medium flow rate; temperature; inoculation period; and length of incubation were established. Similar records in OSTI. GOV collections:.
Full Record Other Related Research. Abstract The overall program objective is to develop and evaluate environmental benign agents or products that are effective in the prevention, inhibition, and mitigation of microbially influenced corrosion MIC in the internal surfaces of metallic natural gas pipelines.
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Authors: J. Paterek ; G. Husmillo ; V. Trbovic Publication Date: Research Org.
Paterek, G. The average sessile cell count for the control was 2. It should be pointed out that exopolymers and dead cells in the biofilm could be utilized by sessile cells as nutrients .
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SEM images here corroborated the sessile cell counts in Fig. Weight loss Fig. The average weight loss after the 2-day pre-growth period was 1. The data here clearly indicate that under carbon source starvation, the biofilm became more corrosive despite the fact that the biofilm sessile cell count decreased significantly Fig.
This means that under carbon starvation, the NRB switched from organic carbon to elemental iron as electron donor . The NRB finding in this work is particularly useful because in the starvation test for SRB, the reduced production of sulfide could lead to less passivation of the steel surface and thus more corrosion.
This complicated the arguments for the effect of starvation. In comparison, NRB starvation test did not have this complication. All the final pH values were above 8. Furthermore, the initial pH values for the culture media before the 2-day pre-growth and the 7-day incubation were all adjusted to 7. Thus, corrosion by secreted organic acids was not a contributing factor in this work.
Pit morphology and pit depth Pit morphologies with biofilms and corrosion products removed after the 2-day pre-growth and after the subsequent 7-day incubation with different carbon source levels are shown in Fig. After the 2-day pre-growth, some small pits can be clearly observed on the coupon surface Fig. The number of pits and pit diameters increased in the control after the 7-day incubation Fig. Larger pits were observed in reduced carbon source conditions Fig.
The pit depth profiles from IFM in Fig. The sessile cells caused more severe corrosion and deeper pitting under starvation Fig. The observations of pit morphology and pit depth showed that sessile cells attacked C steel more aggressively for 13 respiration to survive when limited or no organic carbon were present in the bulk medium. Electrochemical measurements 3. OCP and corrosion rate versus time Fig. The OCP values of the control slightly shifted to the negative direction and then kept steady gradually. The results show that the NRB biofilm was more aggressive when there was a shortage of organic carbon in the medium .
EIS analysis The EIS data were measured under stable OCP for different carbon source levels on the first, the fourth, and the seventh days during the 7-day incubation. The Nyquist and Bode plots are shown in Fig. On the first day Fig. The changes of Nyquist plot diameters in Fig.
The equivalent circuit with a two-time constant model is shown in Fig. These impedance spectra were curve- fitted well. In the equivalent electrical circuit, Rs stands for the solution resistance, Qb and Rb the capacitance and the resistance of the biofilm or the corrosion product film, respectively. Qdl and Rct stand for the double layer capacitance and the charge transfer resistance, respectively. The impedance of constant phase element CPE was employed. The Rct values of the control test were larger than the others during the 7-day incubation.
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The results showed P. Potentiodynamic polarization curve measurements Fig. The corrosion current densities in the reduced carbon source media during the 7-day incubation were larger than that in the control medium which could be associated with a higher charge transfer between the biofilm and the iron surface. The results of potentiodynamic polarization curve measurements were consistent with EIS results and weight loss data. Discussion 16 It is widely accepted that MIC was caused by biofilms because of their metabolic activities or secreted metabolites.
In general, anaerobic MIC can be categorized into two main types based on microbial metabolisms, namely respiration Type I and fermentation Type II . The electron transport chain provides energy in anaerobic respiration . Sessile cells underneath a biofilm on a steel surface may have limited access to the organic carbon in the bulk solution due to diffusional mass transfer hindrance by the biofilm and the utilization of the sessile cells above them in the biofilm.
Therefore, those cells will be forced to switch to elemental iron as the electron donor during carbon source starvation. This proved that SRB sessile cells switched from organic carbon oxidation to iron oxidation by extracting energy from iron to couple its oxidation with sulfate reduction to supply maintenance energy for survival . The use of elemental iron as an electron source for cell growth was proven in evolutionary microbiology outside the MIC research area .
The pH underneath a biofilm can be much lower than that in the bulk phase due to organic acids production. These secreted metabolites are oxidants that can attack iron without biocatalysis. In the oil and gas industry, the abiotic acetic acid attack is a well-known problem . In this work, corrosion by organic acids were not a factor because the NRB underwent respiration instead of fermentation. Furthermore, the pH measured in the bulk medium after the 7-day incubation in different carbon source levels conditions were all above 8 which indicate that the pH underneath biofilms were not acidic enough to cause acid corrosion.
In the control test without decreasing the organic carbon source in the medium, after the 7-day incubation, the P. MIC pitting corrosion was found Fig. The weight loss and maximum pit depth for the control during the 7-day incubation were 1. The P. IFM constructs a 3D image by compiling many 2D images with different focuses to show coupon surface tomography .
It should be noted that IFM still relies on the operator to locate the deepest pit from the 3D image manually. Thus, there is no absolute guaranty that the deepest pit is found by the operator . In this work, the maximum pit depth data were supported by weight loss data. The EIS analysis Fig.
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It should be pointed out that elemental iron is only a fuel rather than food for P. This also pointed out when i. Conclusions P. After 2-day 19 pre-growth, P.
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The corrosion mechanism in this work supported the BCNR theory which is based on bioenergetics. Carbon source starvation led to more aggressive MIC because the starved sessile cells switched to elemental iron as an electron donor. Electrochemical measurements using OCP, LPR, EIS and potentiodynamic polarization were all able to corroborate the weight loss and pit depth data qualitatively.
Thus, properly conducted electrochemical measurements were useful in mechanistic MIC studies. Hassett of University of Cincinnati. Gaines, Bacterial activity as a corrosion induced in the soil, Ind. Coetser, T. Cloete, Biofouling and biocorrosion in industrial water systems, Crit. Liu, D. Xu, A. Dao, G. Zhang, Y. Lv, H. Liu, Study of corrosion behavior 20                 and mechanism of carbon steel in the presence of Chlorella vulgaris, Corros.