Influence of corrosion behavior of X80 steel in silty soil containing composite sodium salt based on orthogonal test

The corrosion law of X80 steel in silty soils with different contents of sodium chloride and sodium sulfate is studied at different temperatures by using an orthogonal test group of three factors and three levels L9 (34) in conjunction with the results of electrochemical impedance spectroscopy, polarization curve, and microscopic images. The steel corrosion rate increases with the silty soil temperature. The presence of SO42− in silty soil inhibits corrosion in X80 steel. The corrosion mechanism involves competition between Cl− and SO42− for adsorption sites: SO42− ions occupy some corrosion pits, and FeS and other corrosion products are generated and adhere to the surface of the corrosion pits, inhibiting further reaction. A range analysis of the fitted electrochemical impedance spectra and polarization curves of X80 steel shows that the temperature has the strongest effect on the corrosion of X80 steel, followed by the Cl− content, whereas the SO42− content has the least effect. The lowest corrosion rate is found for a silty soil Cl− content of 0.3%, a SO42− content of 2.0%, and a temperature of −20°C.