Corrosion mechanism and damage characteristic of Q235B steel under the effect of stray current in NS4 simulated soil solution

Abstract

Dynamic direct current (DC) may cause severe electrochemical corrosion on buried steel pipelines near urban rail transits. In this paper, the corrosion behavior of Q235B steel under dynamic DC interference was carried out in NS4 simulated soil solution (NS4 solution) including potassium chloride (KCl), sodium bicarbonate (NaHCO3), calcium chloride (CaCl2), Magnesium sulfate heptahydrate (MgSO4.7 H2O) and deionized water. The electrochemical corrosion behaviors of Q235B steel in NS4 solution were studied by means of potentiodynamic polarization (Tafel curve) and electrochemical impedance spectroscopy (EIS) techniques. Dynamic DC was simulated by four types of applied current according to the leakage current rule of rail trains arriving at and departing from the platform. The results of Tafel curves showed that Q235B steel exhibits a decrease in corrosion resistance with increasing applied current density, and anodic reaction exhibited active dissolution controlled by charge transfer. EIS results indicated that Nyquist plots of samples included double capacitive arcs and exhibited Warburg impedance characteristics caused by the concentration gradient. Weightlessness measurement showed that the average corrosion rates of four types of samples were 1.0, 1.4, 2.0, and 2.5 g.cm−2. d−1, respectively. In addition, the corrosion morphology indicated that samples featured in pitting corrosion, which was correlated to applied dynamic DC values and counts, and corrosion products were Fe3O4 and Fe (OH)3. Finally, the study shows that corrosion of buried steel pipelines is related to rail train arriving types and counts.