ISO 28721-1:2019

Overview - ISO 28721-1:2019 (glass-lined apparatus quality)

ISO 28721-1:2019 specifies quality requirements and manufacturer test procedures for glass-lined steel and glass-lined steel castings used in process plants. It covers vitreous and porcelain enamel coatings (including semi‑crystallized enamel coatings) applied to apparatus, components, appliances and accessories - such as vessels, columns, glass‑lined pumps, pump components and fittings - used in industrial process plants. The standard applies to new items and to used items that have been re‑enamelled. It does not set the chemical/physical composition of enamels and excludes glass‑lined flanged steel pipes and flanged steel fittings (see ISO 28721‑4).

Key topics and technical requirements

• Quality and design responsibilities: Manufacturer responsibility for appropriate design, enamel type and finish; enamel type and colour to be agreed at order.
• Surface and finish: Enamel must be smooth, uniform and fully fused; provisions for acceptable and unacceptable surface conditions.
• Defect classification and repair: Defines unacceptable defects (e.g., extended defects > 8 mm, devitrified areas, cracks) and repairable defects (e.g., depressions > 25% of coating thickness, blisters, impurities). Specifies limits on plugged defects for vessels and columns and rules for areas that must not be plugged.
• Testing procedures: Includes visual examination, high‑voltage test (with a provision added for a 7 kV test for conductive/dissipative enamels), crack testing, coating thickness measurement, dimensional checks, concentricity measurement for agitators/pump rotors and performance testing.
• Manufacturing inspection, repairs and documentation: Stages for inspection, approved repair methods (plugging, impurity removal), requirements for test reports and examples (Annex A), and guidance on packaging, transport and inspection at delivery.

Practical applications and who uses this standard

ISO 28721-1 is intended for:

• Manufacturers and fabricators of glass‑lined reactors, vessels, columns and pumps
• Quality assurance and inspection teams verifying enamel finish and dimensional conformity
• Plant engineers and maintenance teams specifying equipment for chemical, pharmaceutical, food and process industries
• Procurement specialists writing purchase orders specifying compliance: “Manufactured in accordance with ISO 28721‑1.” Using this standard helps ensure reliable enamel coatings, consistent testing, traceable repair actions and safer, longer‑lasting glass‑lined equipment in corrosive or high‑purity process environments.

Related standards

• ISO 28721‑2 (chemical resistance and thermal shock designation)
• ISO 28721‑3 (thermal shock resistance)
• ISO 28721‑4 (glass‑lined flanged steel pipes/fittings)
• ISO 28721‑5 (defect descriptions)
• ISO 2746 (high‑voltage test), ISO 2178 (coating thickness measurement), ISO 19496‑1 (terminology)

Keywords: ISO 28721-1:2019, glass-lined apparatus, vitreous and porcelain enamels, quality requirements, glass-lined pumps, coating thickness, high-voltage test, defect repair, process plants.