Effects Of The Synergy Of Microorganisms On The Corrosion Of Typical Engineering Steel In Marine Environment

The microorganisms would adhere to the surface of marine engineering and form biofilm in marine environment.Under the synergy of multiple microorganisms in biofilm,the corrosion of marine engineering steel would be effected,resulting in the promotion or inhibition of corrosion.Therefore,it's necessary to study the corrosion of marine engineering steel under the synergy of multiple microorganisms,reveal the mechanism of corrosion and provide guidance to the protection of corrosion.This study investigated the corrosion behavior of typical marine engineering steel through the exposuretest in marine,the simulated experiment in laboratory,and the corrosion experiment under the synergy of aerogenic and aerobic bacteria.It investigated the effects of adding Cu to the matrix on the microbiologically influenced corrosion(MIC)and the feasibility to inhibit it.It revealed the corrosion mechanism through the analysis of microbiology community,the observation of surface morphology,the analysis of corrosion products,and the measurement of environmental parameters.The results are as followed:(1)The effects of the addition of Cu on the corrosion rate and surface microbial diversity of mooring chain steel were revealed in marine environment.The corrosion rates of 3 kinds of samples were different with each other: the average corrosion rate of R5 steel was 0.18 ? 0.005 mm/a,which was the least;the average corrosion rate of R6 steel with a higher and lower content of Cu was 0.24 ? 0.01 and 0.34 ? 0.005 mm/a,respectively.The analysis of microbiology community structure on the surface of samples suggested that the addition of Cu increased the relative abundance of sulfate?reducing bacteria(SRB)on the surface of both R6 samples,which was believed to closely relate to the accelerated corrosion.(2)The effects of multiple microorganisms on the corrosion of mooring chain steel and carbon steel were revealed,and the material dependence of the effects of microorganisms was analysed under the condition of simulated seawater in laboratory.The results suggested that the corrosion behavior of carbon steel and 3 kinds of mooring chain steel was similar in sterile seawater,which were general corrosion induced by the cathodic oxygen depolarization.In seawater with bacteria,the biofilm formed by microorganisms inhibited the corrosion to a certain extent.The microorganism quantity decreased with time,leading to the weakened inhibition.The addition of Cu resulted in the decrease of microorganism quantity on the surface of both R6 samples,but it made little impact on the corrosion behavior.Though corrosion was inhibited in the intial stage,the average corrosion rate of carbon steel was similar with the case in sterile seawater,which could be attributed to the serious pitting corrosion.(3)The mechanism of the corrosion of carbon steel was revealed under the synergy of Synechococcus sp.(S.sp.)and Pseudoalteromonas sp.(P.sp.).In the media containing S.sp.alone,it propagated slowly,and dissolved oxygen concentration and pH maintained relatively stable,resulting in a continuous corrosion of carbon steel.In the presence of S.sp.and P.sp.,corrosion was inhibited in the intial stage by the formation of protective biofilm and the consumption of oxygen by aerobic respiration of P.sp.In the later part of experiment,a serious corrosion on carbon steel was observed due to the death of P.sp.,the rapid reproduction of S.sp.,the increase of dissolved oxygen concentration,and the porous corrosion products,in which the corrosion rate was much higher than it in the media with S.sp.alone.