ELECTROCHEMICAL BEHAVIOUR AND SCC SUSCEPTIBILITY OF PIPELINE STEEL X70 IN NEAR-NEUTRAL AND HIGH pH SOLUTIONS

The influence of temperature,aerated condition and pH value on the electrochemical behavior and stress corrosion cracking(SCC) susceptibility of X70 pipeline steel in NS4 solution and 0.5 mol/L Na2CO3+1 mol/L NaHCO3 solution was investigated using potentiodynamic polarization measurements and slow strain rate tests(SSRT).In NS4 solution,active-passive transition behavior did not appear and SCC susceptibility increased with the negative movement of applied potential,indicating character of hydrogen induced cracking(HIC).In 0.5 mol/L Na2CO3+1 mol/L NaHCO3 solution,active-passive transition behavior was found in the potentiodynamic polarization curves,character of hydrogen induced cracking(HIC) was shown in cathodic polarization region and anodic dissolution SCC(ADSCC) occurred in anodic polarization region.