This part of ISO 28721 specifies requirements for the resistance to chemical attack and thermal shock of chemical enamels and their designation for ordering purposes. It is applicable to enamelled apparatus, piping and other components primarily used for process equipment in chemical plants. It only applies to unalloyed and low-alloy carbon steels suitable for enamelling. NOTE The main criteria for assessing enamel quality are the resistance to chemical attack and thermal shock and the structure of the cover coat enamel.