碳钢和不锈钢在海洋SRB、IRB和IOB下的点蚀研究现状OACSTPCD

Microbiological Induced Corrosion(MIC)occurs due to the interaction of the activities and metabolites of the microorganisms with metal materials,which affects the cathodic and anodic processes of corrosion reactions.This phenomenon accounts for approximately 20%of marine corrosion hazards,rendering it a major technical problem for the marine industry.The study of microbial corrosion in marine environments is of great significance to promote the development of the Chinese marine industry.Microbial corrosion of metal materials includes both comprehensive corrosion and local corrosion,with local corrosion being more harmful.Among various forms of local corrosion,pitting corrosion is considered the most harmful. The marine environment has a wide range of marine microorganisms with diverse functions and characteristics.This article focused on the phenomenon of microbial pitting corrosion,which was caused by the inhomogeneous biofilm,corrosion product membrane of bacteria,and the characteristics of bacteria themselves.In particular,this study explored the role of Sulfate-reducing Bacteria(SRB),Iron-reducing Bacteria(IRB)and Iron-oxidizing Bacteria(IOB)in the aforementioned corrosion process. This paper analyzed pitting corrosion of carbon steel and stainless steel caused by SRB,IRB and IOB,which were widely used in offshore platforms and ships.The corrosion differences of carbon steel and stainless steel in different bacterial systems were compared according to the corrosion morphology and corrosion products.The analysis of corrosion morphology included the analysis of corrosion product morphology and metal surface morphology after removal of corrosion products while the analysis of corrosion products mainly included the changes of different composition and content on the surface of metal materials.The corrosion of carbon steel caused by SRB resulted in the formation of loose porous composite film composed of SRB biofilm and iron sulfide(FexS).The corrosion of stainless steel by SRB resulted in the formation of a double porous surface film,the outer layer of which was a composite film composed of a biofilm and a vulcanized film,while the inner layer was a vulcanized passivation film.Corrosion caused by SRB on carbon steel and stainless steel would lead to uneven adsorption of biofilms on the surface.The difference between carbon steel and stainless steel corrosion caused by IRB was that it changed the composition of the stainless steel passivation film and the composition proportion.After stainless steel was corroded,the composition mainly existed in the form of Cr,Cr2O3,CrO3,Cr(OH)3 and CrN,thus destroying the passivated film.When oxygen concentration was insufficient,damaged passivation film could not be repaired.When IOB corroded carbon steel,the biofilm was dense in the early stage,porous and cracked in the late stage,and the sediment was filamentous.When IOB corroded stainless steel,the biofilm was loose and porous,the biofilm fell off,and the sediment was spongy or needle-like.This paper explained the pitting mechanism of carbon steel and stainless steel from the aspects of metabolite theory and oxygen concentration battery theory.The pitting corrosion of SRB on carbon steel and stainless steel was caused by the formation of local corrosion cells caused by the heterogeneous biofilm and sulfide film of corrosion products.The electrons generated by Fe corrosion were transferred to the cathode region,and the cathode depolarization reaction was promoted,leading to the pitting corrosion of the anode region.The pitting corrosion of carbon steel and stainless steel by IRB was caused by the reduction of the protective Fe3+ oxide to soluble Fe2+ by the oxygen concentration cell formed by the heterogeneous biofilm,which lead to the destruction of the corrosion product film,resulting in pitting corrosion.The pitting corrosion of carbon steel by IOB was due to the formation of many small anode active sites in the substrate under the formed sediment film.Anode Fe loses electrons and transferred to cathode.The depolarization of O2 produced OH‒,and then produced Fe(OH)3 to further promote the dissolution of anode,thus accelerating the pitting corrosion of carbon steel.The pitting corrosion of stainless steel by IOB was due to the production of spongy or needle-like Fe(OH)3,Fe2O3 deposits,which made corrosive ions enter the surface of stainless steel,prevent metal ions from leaving the surface,destroy the surface passivation film of stainless steel,thus promoting pitting corrosion.Finally,this paper proposed that microbial pitting corrosion research should consider a variety of factors comprehensively,including the influence of the interaction of multiple strains and various environmental factors on the pitting corrosion of metal materials,as well as the influence of microorganisms on the pitting corrosion of corrosion resistant metal materials.