Influence of the stainless steel 321 (X18Н10) structure on pitting corrosion in low-mineralized water. Inhibiting effect of sulfate and hydrocarbonate ions

• A.I. Shcherbakov, I.V. Kasatkina, V.E. Kasatkin, I.G. Korosteleva, V.N. Dorofeeva and L.P. Kornienko

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation

Abstract: The study of two austenitic class stainless steels similar in composition and microstructure to the resistance for pitting corrosion in low-mineralized river and tap water showed that steel 321 (Х18Н10T) sheet is more resistant than steel 301 (Х18Н9) pipe. This difference in behavior is due to the presence of different amounts of residual ferrite in these steels, which negatively affects the tendency of austenitic steels to pitting resistance. It is shown that anodic polarization in a solutions containing more than 1.45 mg/L of chloride ion leads to pitting corrosion. When the chloride ion content is more than 21.4 g/L (3.5% NaCl, which corresponds to seawater), the steel pits without polarization. The presence of sulfate ions in the solution reduces or prevents the tendency of steel to pitting. The threshold concentration ratio of sulfate inhibitor to chloride activator for pitting protection depends on the activator content. The higher the chloride concentration, the higher the SO₄^2–/Cl^– ratio is required to inhibit pitting. When the chloride ion content in water is above 100 mg/L, the same amount of sulfate ions is sufficient. At the chloride ions concentrations from 200 mg/L to 500 mg/L, a twice higher sulfate content is required, and at a chloride concentration of up to 3000 mg/L, it is already 3 times higher. Bicarbonate can slightly increase the tendency of steel to pitting corrosion in the absence or with insufficient amount of sulfate inhibitor. At a higher sulfate content, the negative effect of hydrocarbonate is leveled, even if its concentration is 2–4 times higher than the concentration of the inhibitor SO₄^2–.

Keywords: activators and inhibitors of pitting corrosion, AIST 321 (X18H10T) steel, AIST 301 (X18H9) steel, residual ferrite, low-mineralized water

Int. J. Corros. Scale Inhib., 2021, 10, no. 1, 176-185 PDF (566 K)
doi: 10.17675/2305-6894-2021-10-1-10

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