Effect Of Pseudomonas Aeruginosa On Corrosion Behavior Of X65 Pipeline Steel

With the continuous exploitation of marine resources,a large number of engineering materials are used in the marine environment.X65 pipeline steel is widely used in the field of offshore oil and gas exploitation due to its excellent performance.However,due to the complex environment in the ocean,X65 pipeline steel is facing a huge risk of failure,of which corrosion is the most serious failure mode.Microbiologically influenced corrosion（MIC）accounts for 20%of the huge economic losses caused by corrosion.Therefore,it is of great significance to study the corrosion mechanism of X65 pipeline steel by microorganisms for the long-term service and microbial protection of marine engineering steel.In this paper,the corrosion effect of Pseudomonas aeruginosa（P.aeruginosa）secreting phenazine compounds on X65 pipeline steel was studied by weight loss method,biofilm scanning electron microscopy analysis,surface corrosion morphology observation,electrochemical test,medium pH test and X-ray diffraction analysis of corrosion products.X65 steel was subjected to aerobic and anaerobic immersion in the medium without bacteria and containing P.aeruginosa,respectively.The results showed that the inoculation of P.aeruginosa accelerated the corrosion of X65 steel,and P.aeruginosa would generate an alkaline substance in the aerobic environment to corrode the steel surface,and the corrosion degree was more serious than that in the anaerobic environment.Studies have shown that phenazine compounds may be an important carrier of bacterial transport electrons to cause corrosion,and pyocyamin（PYO）is the most important phenazine compound produced by P.aeruginosa.After knocking out the phzM and phzS genes that regulate the synthesis of PYO,P.aeruginosa can still produce biofilms on the surface of X65 steel consistent with the morphology of wild-type P.aeruginosa,but the corrosion of X65 steel is significantly reduced.Under aerobic conditions,the gene knockout P.aeruginosa mineralized on the steel surface,and the mineral was mainly Ca CO₃.After adding exogenous PYO to the culture medium of gene knockout P.aeruginosa,the size of the bacteria growing on the surface of X65 steel became smaller,and the corrosion products were mainly iron oxides,but the corrosion ability was restored,which accelerated the corrosion of X65steel.It is proved that PYO plays an important role in the corrosion process of P.aeruginosa on steel.In addition to completing electron transfer through its own PYO as an electron carrier,P.aeruginosa can also use external nitrate as an electron acceptor to achieve energy supply,thereby accelerating MIC.Different amounts of potassium nitrate were added to the medium containing P.aeruginosa.The scale and morphology of biofilm formed on the steel surface were different with different NO^3-contents.The biofilm formed on the steel surface became denser with the increase of NO^3-content.When the content of NO^3-is greater than 10 m M,the surface of X65 steel is mostly covered by biofilm containing rod-shaped P.aeruginosa,and alkaline corrosion occurs,and the corrosion rate is accelerated.