The European Union directives on drinking water have been extended to include hot water, with restrictions on the presence of chemical elements. A large number of hot water production and storage systems, both in domestic and commercial settings, involve enameled surfaces. It is therefore of significant interest and utmost urgency to determine the behavior of enamel in contact with drinking water.
In the present study, the behavior of enameled steel in contact with drinking water was analyzed. A commercially available enamel, for water heaters, was used.
The enameled surface was exposed to water (conductivity of 5 µs) at a temperature of 95 °C for a total of 35 days. The solution was replaced daily, and mass loss was measured. The total mass loss was observed to be less than 2 g/m², below the threshold limit.
However, it should be noted that the enamel's behavior may vary depending on the chemical composition and structure of the enamel layer, and the aggressiveness of the water.
After characterizing the enamel’s surface microstructure using a scanning electron microscope (SEM), contact tests were conducted with waters of different conductivity levels, revealing a significant difference in mass loss (ranging from less than 2 to about 5 g/m²). Furthermore, tests were carried out using solutions with acidic and alkaline pH.
Using a "reference" water, the tests were repeated with water withdrawals at different time intervals (4, 4, 2, 5, and 10 days). The presence of chemical elements in the water was analyzed by Inductively Coupled Plasma (ICP) analysis. The concentrations remained within the limits established by the European Union.
Lastly, the enamel surface after prolonged contact with water was examined using SEM to identify the type and location of degradation. It was observed that certain calcium-rich structures were particularly critical, as they tend to promote localized attacks.