Effect Of Sulfate-Reducing Bacteria Metabolite Product On Soil Corrosion Behavior Of Pipeline Steel

Microbiological influenced corrosion is an important failure form of buried pipeline.Systematic research have been conducted by domestic and foreign scholars and relevant measures to control microbiological influenced corrosion have been proposed.In the actual engineering,the chemical fungicide is one of the most commonly used methods to inhibit sulfate reducing bacteria?SRB?influenced corrosion of pipeline steel.Killing SRB or reducing their activity are the common approaches for chemical fungicides to control the corrosion rate of steels in the actual engineering.However,although the bacteria have been killed,the effect of SRB metabolites remaining in the inactivated microbial film on the corrosion behavior is unclear.In this paper,the characteristics of the SRB metabolite film and the anaerobic corrosion product film were compared by scanning electron microscope?SEM?and X-ray photoelectron spectroscopy?XRD?.The effect of SRB metabolites on pipeline steel were studied under anaerobic and aerobic conditions with the combination of electrochemical test.The mechanism of SRB metabolites accelerating soil corrosion of pipeline steel was discussed.The main research results are given as follows:1.The morphology and composition of the SRB metabolite film and the anaerobic corrosion product film were compared.The anaerobic corrosion product film was thin.Its main corrosion products were iron oxides Fe₂O₃ and FeOOH,and no sulfur compounds existed.The outer layer of SRB metabolite film was loose while its inner layer was dense.Its main components were iron oxide Fe₂O₃,FeOOH and sulfur compounds FeS,Na₂SO₃,CaSO₄.SRB physiological activity changed the composition and structure of the corrosion products.2.In the anaerobic soil environment,the original corrosion product film had a significant acceleration effect on pipeline steel corrosion in the initial stage,while as the new corrosion product film formed gradually,the corrosion rate of the specimen decreased.The presence of the original corrosion product film changed the anaerobic corrosion process of the pipeline steel.The specimen showed obvious pitting corrosion,tending to join into pieces.Compared with the original corrosion product film,the SRB metabolite film in the anaerobic environment had a greater acceleration effect on pipeline steel corrosion,and the acceleration role can sustain until the end of the experiment.The SRB metabolites resulted in a large local corrosion pit on the specimen surface,and the pits expanded in the form of micro-cracks.3.In the aerobic soil environment,the presence of the original corrosion product film increased the corrosion rate of the specimen in the early stage of the experiment,but the acceleration effect became weak in the later stage.The corrosion rate of the specimens covering SRB metabolite film was consistently higher than those of the other two groups throughout the experiment.SRB metabolites on the specimen surface induced the interconnection of micro-pores corrosion.And the number,width and depth of the micro-pores for the specimens covering SRB metabolite film were larger than those covering the original corrosion product film.4.Under the action of the SRB metabolite film,the corrosion processes of pipeline steel in aerobic environment are different from that in anaerobic environment.The corrosion rates of the control specimen and the specimen covering original product film in aerobic environment were significantly higher than that in the anaerobic environment,indicating that dissolved O₂ significantly accelerated the corrosion process of pipeline steel.However,the specimen covering SRB metabolite film maintained a higher corrosion rate in anaerobic environment,indicating the acceleration role of sulfide on the steel corrosion was more pronounced than that of dissolved O₂ in soil environment.