The Effect Of Marine Biofilm Formation Ability On The Corrosion Behavior Of X80 Pipeline Steel

With the rapid development of the global economy,science and technology,we are trying to seek for the potential resources and energy to meet the needs for the development of human society.The marine resource has become a strategic consensus of all countries in the world.The materials used in marine engineering equipment are seriously threatened by the complex marine environment.The corrosion caused by marine microorganisms accounts for a large proportion of the total corrosion of marine materials,which is a serious concern.X80 pipeline steel has become one of the most widely used steel materials in oil and gas transportation.It possesses excellent properties such as toughness and weldability.However,if it is used in the marine environment for a long time,microbiologically influenced corrosion(MIC)will be a potential threat.It is currently recognized that MIC is mainly caused by the biofilms,and biofilms may also inhibit the corrosion of materials.Therefore,it is of great significance to study the biofilm formation ability and its correlation to the corrosion behavior of materials.In this paper,T.mesophilum D-6,T.litoreum W-4 and Bacillus sp.Y-6 isolated from Fujian seas were selected,and the effects of bacteriabiofilm formation ability on the corrosion behavior of X80 pipeline steel were systematically investigated.The biofilm formation ability of T.mesophilum D-6,T.litoreum W-4 and Bacillus sp.Y-6 on X80 pipeline steel was compared by crystal violet(CV)assay.The biofilm formation ability of the three bacteria was:T.mesophilum D-6>T.litoreum W-4>Bacillus sp.Y-6 Then,the biofilm distribution and biofilm thickness on the coupon surface were observed by scanning electron microscopy and laser confocal microscopy,and the order of the biofilm formation ability was consistent with the conclusion of CV test.Electrochemical experiments showed that T.mesophilum D-6,T.litoreum W-4 and Bacillus sp.Y-6 all increased the Rp and Rct of X80 pipeline steel,indicating that these three bacteria inhibited the corrosion of X80 pipeline steel.The polarization curve also showed that the icorr of X80 pipeline steel was smaller in the biotic system,and T.mesophilum D-6 showed the strongest inhibition effect,T.litoreum W-4 ranked second,and Bacillus sp.Y-6 was the third.Furthermore,it was observed by CLSM that there were pits on the coupon surface in both biotic and abotic treatments.By comparison,it can be shown that the biofilms significantly inhibited pitting corrosion,and the pit depth of T.mesophilum D-6 was the smallest,which also proved that the inhibition effect was the best.The weight loss data also directly indicated that the presence of three bacteria reduced the corrosion rate.X-ray photoelectron spectroscopy tests showed that organometallic complexes were present in the corrosion products in the biotic system.Electrochemical experiments showed that the sample exhibited greater Rp and lower icorr in the presence of EPS.Therefore,it can be concluded that EPS produced by bacteria inhibited the corrosion process by immobilizing metal ions.In addition,the physical barrier effect of the biofilm can block the diffusion of the aggressive ions such as oxygen and chloride.The biofilm may cosume the oxygen by their metabolism and respiration.In summary,the biofilm formation ability of the three marine bacteria in this work was closely related to the corrosion behavior of X80 pipeline steel.T.mesophilum D-6,T.litoreum W-4 and Bacillus sp.Y-6 all inhibited the corrosion of X80 pipeline steel.The biofilm formation ability was corelated with its inhibition effect.We also proved that EPS played an important role in corrosion inhibition process.Our work provides a new idea for controlling and preventing MIC of X80 pipeline steel.Biofim and its EPS can be used as anefficient and environmentally friendly corrosion inhibition method to design new biofilm based corrosion inhibitors.