| LI Xin,SHANG Dong-zhi,LI Zi-mo,JIANG You-wen,CHEN Chang-feng.SRB Corrosion Behavior of L245 Pipeline Steel with Different Cathode Polarization Potential[J],51(7):207-217, 235 |
| SRB Corrosion Behavior of L245 Pipeline Steel with Different Cathode Polarization Potential |
| Received:February 15, 2022 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2022.07.020 |
| KeyWord:cathode polarization SRB biofilm FIB-SEM cross-section pitting field testing showed that |
| Author | Institution |
| LI Xin |
China University of Petroleum, Beijing , China;China Petroleum Pipeline Bureau, Hebei Langfang , China |
| SHANG Dong-zhi |
China University of Petroleum, Beijing , China |
| LI Zi-mo |
China University of Petroleum, Beijing , China |
| JIANG You-wen |
Pipe China North Pipeline company, Hebei Langfang , China |
| CHEN Chang-feng |
China University of Petroleum, Beijing , China |
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| Abstract: |
| The influence of cathode polarization on sulfate-reducing bacteria (SRB) corrosion behavior of pipeline steel has gained great attention from corrosion industry. The difference of microbial corrosion behavior of L245 pipeline steel with different cathodic polarization potentials in SRB containing environment was studied by simulation experiment, and the influence rule and microscopic pitting mechanism of the microbiologically influenced corrosion (MIC) process with polarization potential were explored. Laboratory tests were conducted to elucidate the cathodic reactions and MIC process by different potentiostatic cathodic polarization (OCP, –0.75 V, –0.875 V, –1.05 V) of L245 steel specimens for 7 days. MPN method were used to analyse sessile SRB quantity variation and its metabolism in biofilm, electrochemical measurements method such as open circuit potentiometry and electrochemical impedance spectroscopy (EIS) were applied to analyse the development and changes of morphology and composition of the corrosion product film. In order to investigate the surface and inner composition and structural changes, corrosion products film were cross-sectioned and detected by scanning electron microscope (SEM) and focused ion beam-scanning electron microscope (FIB-SEM&EDS) respectively. Laser scanning confocal microscope (CLSM) were used to analysis the difference of pitting behavior happening under the biofilm with different polarization potentials. This study focuses on MIC process, biofilm development and pitting corrosion caused by an SRB consortium with different CPs using FIB-SEM. Several concluding findings are listed as below:Proliferation of SRB bacteria was not inhibited in the presence of cathodic polarization and corrosion continued in the localized regions under biofilm. With the mild cathode polarization, applying –0.75 V and –0.875 V significantly could promote the SRB metabolic activity, strengthen the adsorption and growth of SRB on the surface of the electrode, greatly increased the number of sessile SRB in biofilm, so the pitting degree was aggravated accordingly, The result at ‒0.875 V was the more significant. Sessile SRB cells, in the corrosion product film formed at mild polarization potentials, were covered with sulfide and organic substance. With the potentials changing from OCP to ‒0.875 V, the thickness of biofilm gradually increased, and the content of bacterial metabolite elements such as S, P also increased. With the condition of strong cathode polarization ‒1.05 V, the upper layer of the corrosion product film was enriched with C, O, Ca elements, which mean that mineralization has occurred. The metabolic activity of SRB was inhibited and the number of sessile SRB cells decreased significantly, so the pitting phenomenon disappeared accordingly. The strong polarization potential inhibited the metabolic activity of bacteria and prevented pitting corrosion happening.The mild cathodic polarization ocould increase the MIC tendency of SRB, while the strong polarization potential inhibited the metabolic activity of bacteria and prevented the pitting corrosion occurring. The mechanism that the pitting degree was aggravated by the effect of cathode polarization potential on the metabolic activity and quantity of sessile SRB in biofilm was revealed. The enhancement of metabolic activity of SRB underneath the biofilm are the results of SRB's direct acquisition of electrons from the metal surface, H+ from microbial activities of SRB cells in biofilm accumulated underneath the biofilm and led to pitting corrosion. |
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