Influence of specific magnetic susceptibility of AISI 304 steel on its pitting resistance in the model circulating waters

The influence of the parameters of the chloride-containing media and the specific magnetic susceptibility of AISI 304 steel on its pitting resistance in model circulating waters with pH 4 and chloride concentrations of 300 and 600 mg/L is investigated. Chlorides are often found under scale or precipitate from circulating water on the heat transfer elements of heat exchangers made of this steel. The critical pitting temperature (CPT) of AISI 304 steel slightly (5–6 °C) decreases with an increase in the specific magnetic susceptibility χ₀ of austenite from 2.23×10⁻⁸ to 2.31×10⁻⁸ m³/kg. In particular, the CPT of AISI 304 steel is greater than the parameter χ₀. It was also established that CPT increases intensively by 10–13 °C when the pH of model circulating waters increases from 4 to 7, and with pH 8 it is the same and even lower than with pH 4. Corrosion losses of chromium, nickel, and iron from pittings in model circulating waters with pH 4 and chloride concentrations of 300 and 600 mg/L significantly depend on χ₀ of steel, which is caused by the repassivation of metastable pittings on its surface and the redistribution of current density in stable ones.