Porcelain enamel is a fully inorganic finish, essentially glass, which is fused to the steel at temperatures ranging from 800°C to 900°C thus providing an outstanding protection against corrosion of hot water. At these high temperatures a strong bond is created between steel and the impervious enamel surface and unique properties are imparted. For his resistance to open flame Porcelain Enamel is infact also called FirenamelTM . This superior coating material is not to be confused with all other enamels of organic origin firing at red colour would destroy.

Informations of this bulletin apply to storage vessels for hot water, heated both directly by electricity or gas and, if combined with boilers for home heating, indirectly by hotter water flowing through a built in heat exchanger mainly a spiral tube type.Hot water tanks will be here further called also with the commonly used short name of "boilers".