Corrosion behavior of X70 pipeline steel in simulated Ku'erle soil solution with CO₂

The effect of CO₂ on the stress corrosion cracking (SCC) behavior of X70 pipeline steel in simulated Ku'erle soil solution was investigated by polarization curve, EIS and slow strain rate testing (SSRT). The morphologies of fracture surface of X70 pipeline steel in the solution with the different partial pressures of CO₂ were analyzed by SEM. The results show that the dissolved CO₂ reacted with the corrosion product of FeCO₃ and a dissolved complex (Fe(CO₃)₂^2-) is formed. The cathodic regime representing evolution of hydrogen is also affected by the presence of dissolved CO₂. The SCC of X70 pipeline steel in dissolved CO₂ solution follows the mechanism of hydrogen-facilitated dissolution. As the increase of the pressure of CO₂ in the solution, the effect of hydrogen induced cracking is enhanced.