Corrosion Behavior And Mechanism Of Film-Formed X80 Pipeline Steel Under Synergistic Effect Of SRB And Stress In Guangzhou Soil Environment

X80 pipeline steel is widely used in the second-line project of China West-East Gas Pipeline because of its high toughness,high strength and good welding performance.As one of the gateways of the Second West-East Gas Pipeline Project in Guangzhou,Guangzhou soil is a typical acid red-red soil in South China.The soil has high water content and suitable temperature,which provides a good environment for the growth of SRB,and is a high-incidence zone for stress corrosion cracking of high-strength pipeline steel.This paper cultivated SRB after enrichment and purification from Guangzhou soil.The number of SRB in Guangzhou soil was determined by MPN method.The growth law of SRB in Guangzhou soil was studied,and the growth curve of SRB in a growth cycle was measured.The results showed that the amount of SRB in Guangzhou soil was about 7.6×10 ~4/mL,and the SRB cells were arc-shaped and belonged to Gram-negative bacteria.During a growth cycle,SRB growth in Guangzhou soil can be divided into growth retardation phase,logarithmic growth phase,stable growth phase and decay phase.Based on AC impedance technique,cyclic polarization technique and energy spectrum analysis technology,combined with scanning electron microscopy(SEM)and atomic force microscopy(AFM),the different surface layers of the electrode surface were characterized.The results show that in the soil environment,the initial film formation time of biofilm represented by SRB is 72 hours,and the mature and dense biofilm is formed at 120h with the thickening of the film layer;The corrosion rate of X80 steel in the process of biofilm formation is firstly reduced,then increased and then decreased.More dense and mature biofilms can reduce the corrosion sensitivity of pipeline steel.At the same time,using the AC impedance technique and the cyclic polarization technique,the self-made"stress-electrochemical corrosion test device"was used for the slow strain rate tensile test,and the fracture morphology was characterized by scanning electron microscopy(SEM).The results show that the applied stress is much larger than the polymerization force between the biofilm components,and the stress makes the biofilm formation on the electrode surface more difficult,and the stress corrosion sensitivity of X80 steel in the acidic soil environment shows a certain regularity:5d<1d<2d<4d<3d;The stress corrosion mechanism of X80 steel in the SRB-containing acidic soil environment is anodic dissolution,and the fracture morphology is ductile fracture.Biofilms alter the corrosion properties of the electrode surface by altering the surface roughness of the electrode and affecting the transfer of ions in the corrosion system.In this study,the growth pattern of SRB in the soil environment of Guangzhou and the film formation time of X80 steel surface biofilm were investigated.The morphology of biofilm and its interaction with the metal under the film of X80 steel in the soil environment of Guangzhou under the synergistic effect of SRB and load were analyzed.The existing research is supplemented to provide a scientific reference for the theoretical model of stress corrosion cracking of X80 pipeline steel in China's acidic soil environment containing SRB biofilm.