Effects Of Sulfate-reducing Bacteria On Corrosion Behavior Of X80 Pipeline Steel In Soil Environment

Microbial corrosion is one of the main influence factors for pipeline steel corrosion behavior in soil environment.Thereinto,the effect of anaerobic sulfate-reducing bacteria(SRB)on corrosion for pipeline steel is the most significant.At present,X80 pipeline steel is considered to be the future choice of natural gas transportation.However,the probability of occurrence of buried pipeline corrosion increases,there is bound to corrosion phenomenon,which is a serious threat to safe operation of the buried pipeline.Especially the possibility of SCC behavior of X80 pipeline steel increases greatly in the soil containing SRB environment.So it is very necessary to study the effect of active SRB in soil environment on the corrosion behavior of X80 pipeline steel,and make clear of the corrosion mechanism and relationship between SRB and the SCC sensitivity.In this article,SRB were concentrated successfully from the actual soil of Yingtan,Shenyang and Dagang.The growth curves of SRB in three soil environment were obtained.The morphology of SRB was observed by the biological microscope.The process growth of SRB and the effect of SRB on the environment corrosion factors were studied.Experimental results showed that SRB were the gram negative bacteria which was a kind of desulfovibrio.The quantity of active SRB were relevant to the main corrosion environmental factors of the soil,such as hydrogen sulfide,sulfate ion,E(S),p H and so on.The different growth stages influence of SRB films on corrosion behavior of X80 steel in Shenyang soil was investigated by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and electrochemical impedance spectroscopy(EIS).The results showed that When soaked early,the electrode surface of sample was given priority to with SRB biofilm adsorption,the biofilm was able to slow X80 steel corrosion reaction.With the increase of immersion time,there was a small amount of biofilm and corrosion product film on the electrode surface.At this time,the corrosion of metal was more serious.This was due to the formation of corrosion product film destroyed the original biofilm,which cloud protect the metal.When soaked for 240 h,there was a dense product film on the metal surface,which cloud inhibit the corrosion reaction.Protective effect of corrosion product film was much greater than SRB biofilm for X80 steel.Slow strain rate testing(SSRT)and electrochemical measurement technique were emp1 oyed to study the effect of SRB concentration on the corrosion behavior of X80 pipeline steel.Fracture surfaces were observed by scanning electron microscope(SEM).The results showed that the more active SRB concentration was great,the more metal corrosion behavior was serious.SRB could promote the occurrence of pitting corrosion phenomena.When there was the combination of stress,SRB played a catalytic role on the metal of stress corrosion cracking behavior.The effects of applied potential on stress corrosion cracking(SCC)of X80 steel under SRB and stress action were investigated by homemade "the device of stress loading and electrochemical measurement at constant temperature",EIS,SSRT and SEM.The results showed that when the potential was-850 mV,the metal was in a certain state of cathodic protection.When the potential were self corrosion potential and-650 mV,the crack generation mechanism of X80 steel was attributed to anodic dissolution,SRB cloud accelerated the formation of the corrosion pits.When the potential was-1200 mV,the SCC mechanism was hydrogen embrittlement.Due to the presence of SRB,the hydrogen cloud easily diffuse into the interior of metal.Hydrogen permeation testing with Devanathan-Stachurski cell and SEM analytical method were used to study the influence of SRB on hydrogen permeation behavior of X80 steel in Yingtan soil solution.The result showed that hydrogen permeation current density of X80 steel in soil with SRB was 3-4 times in the soil without SRB.The hydrogen permeation of the metal in the soil could be accelerated respectively by active SRB and the cathodic potential added to the specimens.