Microbiological Influenced Corrosion Of X80 Pipeline And Weld Microstructure

Microbiologically influenced corrosion（MIC）is one of the main corrosion failure forms of oil and gas pipelines in the environment such as soil and seawater,which poses a serious threat to the safety and reliability of pipelines.MIC has caused a large number of problems in the petrochemical and nuclear power industries,and has been listed as a key research project by all sectors of society.However,MIC involves complex chemical and electrochemical interactions between bacterial cells,metabolites,biofilms and matrix metals,with many influencing factors.The MIC mechanism remains controversial.Under the background of the serious corrosion failure of oil pipelines caused by microorganisms,X80’s SRB corrosion mechanism and protection measures were explored.Three research experiments were mainly carried out.It is hoped to provide theoretical basis and protection methods for MIC evaluation and protection of high-strength pipeline steel.This paper mainly uses environmental scanning electron microscopy（SEM）,laser confocal（CLSM）,metallographic microscope（OM）testing techniques.A variety of electrochemical analysis and testing techniques including CV,linear polarization resistance（LPR）,electrochemical impedance spectroscopy（EIS）,cyclic voltage and POL are used for experimental research.The characteristics of the biofilm and the interface between the metal-medium and microbial membranes were used to reveal the corrosion mechanism of X80 under SRB and to study the protective performance of antibacterial coating Cr-Ni-Mo.This work mainly includes the following three experiments:（1）Corrosion behavior of X80 under the synergistic action of sulfate reducing bacteria（SRB）and bentonite;（2）Corrosion behavior of X80 welded joint under the action of SRB in seawater;（3）SRB in seawater protective properties of antibacterial Cr-Ni-Mo coating under the action.The experimental results show that:in the initial stage of SRB colony and extracellular polymer（EPS）formation,the barrier effect of EPS inhibits the corrosion process of steel;after the formation of SRB biofilm,the chemical activity at the metal interface is changed,and the self-corrosion potential of the metal is reduced by about20mV;Complexation and chelation between biofilm and corrosion products Fe²⁺/Fe³⁺,and direct or indirect electronic interactions between cells and their metabolites sulfide and metal,these interactions are coordinated with each other,which promotes the local corrosion under the biofilm Happen and develop.chelation between biofilm and corrosion product Fe²⁺/Fe³⁺.There are direct or indirect electronic interactions between cells and their metabolite sulfides and metals.These interactions synergistically promote the occurrence of local corrosion and development under the biofilm.1.Corrosion experiment results of X80 pipeline steel under the synergistic effect of SRB and bentonite show that after SRB adapts to the environment,the self-corrosion potential of X80 steel in the inoculation environment is about 30mV lower than that in the sterilization environment.Corrosion process;SRB and its biofilm in the late soaking period significantly increase the corrosion rate of X80 steel.SRB biofilm and some metal ions in bentonite and Fe²⁺/Fe³⁺dissolved by X80 have complexation and chelation.Bacteria and their metabolites sulfide and bentonite refractory metal ions precipitate on the metal surface.Use local galvanic cells to accelerate the dissolution of the metal surface,these effects are coordinated with each other,which greatly promotes the occurrence of pitting corrosion.2.The SRB corrosion test results of X80 manual TIG welded joints under the action of SRB in seawater show that:SRB in seawater significantly accelerates the corrosion of welded joints.The welded joints of X80 plate made by manual TIG welding have an active structure and are easily captured by SRB.The electrons accelerate SRB corrosion,and at the same time,the welded joint has rich defects,which provides more active sites for the occurrence of pitting corrosion and accelerates the progress of pitting corrosion.3.The corrosion test results of antibacterial coating Cr-Ni-Mo under the action of SRB in seawater show that:Cr-Ni-Mo coating shows good anti-corrosion performance,and its anti-corrosion effect is about ten times that of X80 pipeline steel.Has good SRB tolerance.The metallic element Cr in the coating forms a passivation film with Cr₂O₃ and Cr（OH）₃ as the main components on the surface of the sample,which isolates the substrate from contact with aggressive ions represented by Cl^-,and reduces the absorption of SRB from the substrate.The role of electrons improves the material’s corrosion resistance.The metallic element Mo in the coating can adhere to the cell wall of bacterial cells to form a complex,which causes the cell wall to rupture and die.At the same time,the enrichment of Mn element also plays a good role in sterilization effect.