Электрохимия, 2022, T. 58, № 7, стр. 420-420

CONCLUSIONS

The through porosity and initial corrosion behavior of enamel coating on carbon steel are characterized by EIS in the dilute sulfuric acid and synthetic tap water at 80°C, respectively. The main conclusions can be drawn as follows:

Many defects such as various pores form in the enamel coating on the inner tank of electric water heater. The coating porosity induced by the through defects can be evaluated simply by using in-situ EIS technique in the hot solution 0.1 mol L^–1 H₂SO₄ + 0.2 mol L^–1 NaCl. The porosity value stabilizes at about 0.0076% within 24 to 48 h, but will change in the evolution processes of capillary penetration, corrosion propagation and corrosion products accumulation.

The through coating defects provide the fast pathways for solution penetration and the locations for forming the occluded corrosion cell on the underlying steel. After about 442 h of immersion in the hot tap water, the steel corrosion under the enamel coating defects may attain a steady state and is controlled by the oxygen diffusion. In the corrosion process, the anion ions such as Cl^–, ${\text{SO}}_{4}^{{2 - }}$, and ${\text{HCO}}_{3}^{ - }$ migrate into the occluded pits, whereas the corrosion products loosely deposit in the pits and gradually transfer to the enamel coating surface via the through defects. As a result, the occluded zones show very low resistances to both ionic transport and active corrosion. But the enamel coating generates no galvanic couple effect on the localized corrosion due to its insulating properties.

This is an excerpt of the article “Initial Corrosion Characteristics of Enamel Coated Carbon Steel in Hot Tap Water.” Full text of the paper is published in Russian J. Electrochemistry, 2021, vol. 57, p. 636.