Effect of cathode potentials on stress corrosion behavior of X80 pipeline steel in simulated alkaline soil solution

Slow strain rate testing (SSRT), potentiodynamic polarization and electrochemical impedance technology were employed to study the stress corrosion cracking (SCC) behavior of X80 pipeline steel at different cathode potentials in Ku'erle soil simulated solution. Fracture surfaces were observed by SEM under applied cathode potential conditions. The results show that the SCC sensitivity of the metal first decreases but then increases with the reduction of cathodic potential. The cracks are generally initiated at corrosion pits with open circuit potential. The crack generation mechanism of X80 steel is attributed to anodic dissolution. When the applied potential is from -0.80 V to -0.95 V, the metal exhibited lower SCC sensitivity under the potential area and their cracking generation mechanism is anodic dissolution and hydrogen embrittlement. When the cathode potential is -0.90 V, the metal is protected. When the applied potentials are -1.0 V and -1.2 V, the process of hydrogen evolution plays the dominant role in SCC occurrence, meaning that the SCC mechanism is hydrogen embrittlement. Moreover, SCC susceptibility increases with the decrease of the applied cathodic potential.