The influence of chloride ion on the corrosion of metal under coating with scratch defects was researched by wire beam electrode (WBE) technology and electrochemical impedance spectroscopy (EIS) technology. The results showed that the current of metal surface could be characterized by the WBE technology. In the case of scratches on the coating, the location of the damage always showed an anodic current, and the cathodic reaction took place adjacent to the damaged location. The cathode area surrounded the defect and migrated to the far end over time. With the increase of Cl- concentration, the corrosion reaction speeded up, the rate of cathode migration also increased, and the speed of coating stripping did as well. Combined with electrochemical impedance spectroscopy, uniform laws were obtained.
Background
At present, microorganism has been considered as important factors that threaten to buried pipelines with disbonded coatings. Aiming at the problem of unknown corrosion mechanism of sulfate-reducing bacteria (SRB), a series of studies have been carried out in this paper. Spectrophotometer and fluorescent labeling technology are used to study the growth and attachment of SRB in the simulated soil solution. The corrosion behavior of X80 pipeline steel with or without SRB was researched by electrochemical methods such as open circuit potential, dynamic potential polarization curve, and electrochemical impedance spectroscopy. The microscopic morphology of the corrosion products on the surface was observed with a scanning electron microscope (SEM), and the element content of the corrosion products on the surface of the sample after corrosion was observed using X-ray energy spectrum (EDS) analysis.
Results
The results showed that the growth and reproduction of SRB caused the pH of the soil simulated solution to increase, which may promote the corrosion of X80 steel. In addition, the cathode reaction of X80 steel in a sterile environment is the reduction of H+, and the main corrosion product is iron oxide. When the soil simulation solution contains SRB, the cathodic reaction is controlled by both H+ reduction and sulfide depolarization reactions, and FeS appears in the corrosion products.
Conclusion
Although the life cycle of SRB is only about 14 days, the corrosion of X80 steel is greatly promoted by SRB, and even causes corrosion perforation, which will bring huge economic losses and serious safety hazards.
Background: At present, microorganism has been considered as important factors that threaten to buried pipelines with disbonded coatings. Aiming at the problem of unknown corrosion mechanism of sulfate-reducing bacteria (SRB), a series of studies have been carried out in this paper. Spectrophotometer and fluorescent labeling technology are used to study the growth and attachment of SRB in the simulated soil solution. The electrochemical behavior of X80 pipeline steel with or without SRB was researched by electrochemical methods such as open circuit potential, dynamic potential polarization curve, and electrochemical impedance spectroscopy. The microscopic morphology of the corrosion products on the surface of the sample was observed with a scanning electron microscope (SEM), and the element content of the corrosion products on the surface of the sample after corrosion was observed using X-ray energy spectrum (EDS) analysis. Results: The results showed that the growth and reproduction of SRB caused the pH of the soil simulated solution to increase, which promoted the corrosion of X80 steel. In addition, the cathode reaction of X80 steel in a sterile environment is the reduction of H+, and the main corrosion product is Fe oxides. When the soil simulation solution contains SRB, the cathodic reaction is controlled by both H+ reduction and sulfide depolarization reactions, and FeS appears in the corrosion products. Conclusion: Although the life cycle of SRB is only about 14 days, the corrosion of X80 steel is greatly promoted by SRB, and even causes corrosion perforation, which will bring huge economic losses and serious safety hazards.
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