Role of Hydrogen in Stress Corrosion Cracking of X-60 Pipeline Steel in Soil Containing Water

The role of hydrogen and anodic dissolution in stress corrosion cracking (SCC) of API X-60 pipeline steel in soil containing water has been studied. The results show that the relative elongation reduction induced by hydrogen, I_HE, increases linearly with increases in the logarithm of hydrogen concentration, C_H, i.e., I_HE(%) = 27.9 + 11.5 lnC_H(wppm). Hydrogen can enter the sample during SCC in soil containing water at open circuit and cathodic polarization. Therefore, the relative elongation reduction during SCC, I_SCC, is the sum of I_SCC(H), I_SCC(AD), and I_SCC(HAD), i.e., I_SCC = I_SCC(H) + I_SCC(AD) + I_SCC(HAD), where I_SCC(H) is the relative elongation reduction induced by the hydrogen that entered the sample during SCC, I_SCC(AD) is that induced by the anodic process during SCC, and I_SCC(HAD) is that caused by the coupling of hydrogen and the anodic process in a hydrogen-enhanced anodic process. For SCC at open circuit, there is no hydrogen-enhanced anodic dissolution, and I_SCC = I_SCC(H) + I_SCC(AD). Experiments showed that I_SCC(H) ≈ I_SCC(AD), indicating that hydrogen and anodic dissolution play almost equally important roles during SCC of pipeline steel in soil containing water at open circuit.