This document specifies the quality requirements for apparatus, components, appliances and accessories of glass-lined steel (including semi-crystallized enamel coatings) and glass-lined steel castings used for process plants. It specifies the quality requirements and the tests to be carried out by the manufacturer as well as the action to be taken to repair defects. The test methods specified cover checking the enamel, the dimensional accuracy and the performance of apparatus and components. The International Standard ISO 28721-1:2008 has been prepared by Technical Committee ISO/TC 107 "Metallic and other inorganic coatings" and has been adopted without any modifications as EN ISO 28721-1:2011 by the Technical Committee of the European Standardization organization, CEN/TC 262 "Metallic and other inorganic coatings", the secretariat of which is held by BSI (United Kingdom). The responsible German committee is Working Committee NA 062-01-63 AA "Prüfung von Emails und Emaillierungen" ("Testing of vitreous and porcelain enamels") at the Materials Testing Standards Committee (NMP) at DIN.