Study On Sulfate Reducing Bacteria Corrosion Behavior Of AZ31B Magnesium Alloy Anode In Tidal Flat Environment

With the development of oil and gas exploitation in coastal shoals,more and more oil and gas pipelines are involved in the sea.As a common metal material in cathodic protection,corrosion problems of magnesium alloy anode can not be ignored.Beach environment is a kind of environment with very high corrosion risk due to complex composition and intense microbial activity.However,there are few reports on the effects of microorganisms on magnesium anode corrosion in beach environment.In this paper,the influence process of microbial corrosion on the abnormal failure phenomenon of sacrificial anode of buried pipeline in tidal flat environment was discussed,and the influence of the change of water content,the change of organic carbon source and the different metabolites of sulfate reducing bacteria on magnesium alloy corrosion was studied:1.Effects of different dry humidity and oxygen content on sulfate reducing bacteria and magnesium alloy corrosion in simulated tidal flat environment: the experimental environmental parameters were determined by field testing of the water quantity in the tidal flat environment.The MPN counting method was used to study the growth of sulfate reducing bacteria in the tidal flat environment under different seawater content.The effect of the change of water content on the corrosion of AZ31 B magnesium anode by sulfatereducing bacteria was investigated by electrochemical method,weight loss experiment,biological test and surface analysis techniques.Sulfate-reducing bacteria can grow well in beach environment and cause microbial corrosion of magnesium alloys.The results showed that with the increase of water content,the number of sulfate-reducing bacteria in soil increased,and the corrosion rate of AZ31 B magnesium anode increased.Compared with the corrosion rate of 0.554 mm/y in 40% water content,the corrosion rate of magnesium alloy sample in 60% water content was as high as 1.38 mm/y.2.The effect of sulfate-reducing bacteria on the corrosion performance of magnesium anode under "starvation" condition was simulated: The corrosion behavior of AZ31 B magnesium alloy cathode material induced by SRB in the absence of organic carbon source due to the presence of filler around the anode was analyzed by electrochemical method,combined with the weight loss and pitting data.The growth of SRB in different organic carbon sources was studied by MPN counting method.The weight loss experiment results showed that the sample with 10% organic carbon source content had the highest weight loss,while the sample with 100% organic carbon source content had the lowest weight loss.The results showed that the corrosion of AZ31 B magnesium anode by sulfate-reducing bacteria under starvation conditions could be explained by the effect of extracellular electron transfer microorganisms on the corrosion mechanism.3.The effects of different metabolites of sulfate reducing bacteria on magnesium alloy corrosion process were investigated.The effects of inorganic and organic metabolites of sulfate reducing bacteria in seawater with different concentrations on magnesium alloy anode corrosion process were analyzed by open circuit potential,electrochemical impedance spectroscopy,polarization curve and other electrochemical methods,combined with scanning electron microscopy,X-ray diffraction and other characterization methods.The results show that the corrosion product film produced by magnesium alloy anode cannot hinder the corrosion process,and different metabolites will accelerate the corrosion of magnesium anode matrix.