Experimental Study On MIC (SRB/TGB) Of Oil Pipeline Steels

Carbon steel,as a relatively low-cost,good weldability and high strength steel,is widely used in various industries.However,the use of carbon steel and microbiologically influenced corrosion(MIC)in oil pipeline will greatly reduce its service life and pose a serious threat to its safety and reliability.At the same time,there are many types of microorganisms in nature,and different types of microorganisms also have a mutually beneficial symbiotic relationship,and their symbiosis may further increase MIC.At present,the understanding of the MIC mechanism among microbial communities is not comprehensive.This article will take MIC of oil field gathering and transportation pipelines as an example to carry out research in order to provide useful exploration for the effective prevention and control of MIC.In this thesis,weight-loss method,scanning electron microscope,confocal laser scanning microscope,X-ray photoelectron spectroscopy and electrochemical test methods(open circuit potential,electrochemical impedance spectroscopy,polarization curve)were used to study the effect of mixed microorganisms and the single strain of sulfate reducing bacteria(SRB)and total general bacteria(TGB)on the corrosion behavior of carbon steel.Firstly,in the single-strain system of SRB and TGB,both of them can result in MIC pitting.Sulfate reducing bacteria can induce serious MIC,the corrosion rate was0.818 mm/a,which was 8 times as high as that of sterile blank group.Moreover,it caused serious pitting,and the maximum pit depth was as high as 49.12?m(2.24 mm/a).However,TGB did not aggravate the extra uniform corrosion rate of carbon steel,and the corrosion rate was equivalent to that of sterile blank group,reaching 0.079 mm/a.It caused MIC pitting,with the maximum pit depth of 16.34?m(0.75 mm/a).SRB obtain the electron of carbon steel matrix to maintain the bioenergetic requirement for life,which accelerates MIC.TGB use oxygen as electron receptor to maintain the energy for life,which catalyzes MIC pitting.In addition,mixed microorganisms caused most serious MIC.Corrosion rate was as high as 1.433 mm/a,and the maximum pit depth was 63.16?m(2.88 mm/a).The MIC mechanism is that TGB can create local anaerobic environment for SRB,which is favorable to growth of SRB,and accelerates MIC pitting.X-ray photoelectron spectroscopy analysis shows that TGB can biocatalyze Fe to Fe²⁺or Fe³⁺and then accelerates MIC.Screening and evaluation of biocides made in our own laboratory were conducted.The study found that different bacteria had different sensitivity and resistance to different biocides.An excellent biocide should have both sterilization and corrosion inhibition effects.It was found that some biocides effectively reduced the number of bacteria,but they accelerated MIC and pitting due to unable to dissociate complete biofilm providing defense and excellent survival environment for bacteria.The findings of this study prove that there is one-sided in the study of single microorganism about MIC.Single species of microorganisms may not be corrosive and can cause serious microbial corrosion synergism with other microorganisms,which provides a new understanding and thinking for the investigation of the MIC mechanism of mixed microorganisms and a certain theoretical basis for the protection of MIC.Moreover,the screening and evaluation of biocides should be conducted from various aspects,and different detection methods from multiple perspectives should be used for optimization,which can select high-efficient biocides for industrial applications.