Influence of alternating voltages on passivation and corrosion properties of X80 pipeline steel in high pH 0.5 mol L − 1 NaHCO 3 +0.25 mol L − 1 Na 2 CO 3 solution

X80 steel exhibits two different steady states in 0.5 mol L− 1 NaHCO3+0.25 mol L− 1 Na2CO3 solution with and without precathodic polarisation, which are activation and passivation respectively. Different amplitudes of alternating voltages were superimposed to the pre- and non-prepolarised steels. The results demonstrated that passivation of the non-prepolarised steel was enhanced by low amplitude alternating voltages but was destroyed by high amplitude alternating voltages. Moreover, the corrosion of the prepolarised steel was worsened with the application of alternating voltages.