Initial Corrosion Characteristics of Enamel Coated Carbon Steel in Hot Tap Water

The corrosion behavior of enamel coating on carbon steel was investigated in the tap water at 80 degrees C (i.e., the simulated electric hot water tank environments) by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and electrochemical measurement techniques. The through porosity of enamel coating is about 0.0076%, simply measured by in-situ electrochemical impedance spectroscopy (EIS) in the dilute sulfuric acid solution. The through defects facilitate the solution penetration in the coating and the formation of occluded corrosion cell on the steel substrate in the hot tap water. The occluded zones have low resistances to both ionic transport and active corrosion. The steady steel corrosion is controlled by the oxygen diffusion via the enamel coating defects, which is accompanied by the transport of anion ions and corrosion products.