Pitting corrosion behavior of X70 steel in weakly alkaline solution under dynamic DC interference

Abstract

Stray current discharged into the soil when subway trains operate will lead to fluctuation in the pipe-soil potential, which causes severe corrosion. In this work, the pitting corrosion behavior of X70 steel in a weakly alkaline simulated soil solution under different potential fluctuation ranges was studied. The influence of the fluctuation of the pipe-to-soil potential on the passivation film and pitting corrosion was studied using electrochemical measurement and surface characterization. X70 steel has passivation characteristics in the weakly alkaline solution. The passivation film is in a dynamic process of continuous growth or growth-dissolution due to the alternating polarization. The critical factor in inducing pitting corrosion is the failure to produce stable and dense passivation film or the instantaneous polarization potential exceeding the range of passivation potential. The passivation film's density determines the pitting's initiation and development trend. It is preliminarily found that the charge transfer resistance at the initiation stage of pitting has a good exponential function relationship with the pitting rate at the stable development stage, which is of great significance for the qualitative evaluation of the pitting rate.