Study On The Influence Of Applied Tensile Stress On Electrochemical Behavior Of X80Pipeline Steel’s Pitting Corrosion

X80pipeline steel, as the main kind of steel to transport oil and gas in21th century, usuallyoccur pitting corrosion firstly in the alkaline soil environment. Pitting corrosion not only has ahigh penetrating rate, but also the pit is the main source of other corrosion damages. There are alot of researches about the environmental effects on pitting corrosion behaviors, such as pH,temperature, Cl-concentration and so on. The influence mechanism also reached consensus.Though the pipeline steel in the service process must be accompanied by stress, the appliedstress influence on the pitting has less research and its mechanism does not to be drawn aconclusion, for example, the applied stress promotes or inhibits on the pitting corrosion has notbeen cleared, and its mechanism has not reached a consensus.According to the theory of pitting nucleation and growth, this thesis studied the effect ofdifferent tensile stresses （0MPa,50MPa,100MPa,200MPa,400MPa） no the X80pipeline steelpassivation and pitting corrosion electrochemical behavior, with or without Cl-environment, anddiscussed the influence mechanism of applied tensile stress to the formation of passivity film andthe production of pitting. The main conclusions are as follows:（1） In0.5mol L^-1NaHCO₃solution, the results of polarization curve, impedancespectroscopy and Mott-Schottky plot indicated that: under tensile stress, the formation ofpassivity film formed on X80pipeline steel was promoted, but its role in promoting increasedfirst and then decreased; the formation of passivity film reached the maximum when σ=100MPa;（2） Under different applied tensile stress, the results of polarization curve and impedancespectroscopy in0.5mol L^-1NaHCO₃+0.0075mol L^-1NaCl solution proved that the pittingcorrosion was inhibited when low tensile （σ≤100MPa） was insisted, the pitting corrosion waspromoted when high tensile （σ≥200MPa） was insisted;（3） In0.5mol L^-1NaHCO₃+0.2mol L^-1NaCl solution, the electrochemical noises of X80pipeline steel under different applied tensile stresses was analyzed: compared to the X80pipelinesteel under low tensile stress （σ≤100MPa）, the X80pipeline steel without stress was corrodedfirstly; on the contrary, compared to the X80pipeline steel without stress, the X80pipeline steelunder high tensile stress （σ≥200MPa） was corroded firstly;（4） The mode of the influence of applied tensile stress on electrochemical behavior of X80pipeline steel’s pitting corrosion was put forward: the interaction of reciprocal inhibition betweenthe passivity film formation and Cl-corrosion leads to low tensile stress （σ≤100MPa） can inhibitthe pitting corrosion while high tensile stress （σ≥200MPa） can promote the pitting corrosion.