Overview
EN ISO 28721-3:2011 - "Vitreous and porcelain enamels - Glass-lined apparatus for process plants - Part 3: Thermal shock resistance" specifies requirements and procedures for assessing and using glass-lined apparatus (glass-lined steel, components, accessories and pipes) subjected to rapid temperature changes in process and chemical plants. The standard covers thermal shock limits, and heating/cooling procedures, and applies to enamelled unalloyed and low-alloy carbon steels for operating temperatures from −25 °C to +230 °C.
Key topics and requirements
- Thermal shock diagrams: Graphical limits are provided for thermal shocks on the glass-lined side (product contacting the enamel) and on the steel side (heating/cooling medium in the jacket). These diagrams define safe combinations of:
- Wall temperature (TW) - average steel temperature of the enamel
- Product temperature (TP)
- Temperature of heating/cooling medium (THC)
- Shock media: Defines a shock medium (e.g., steam, aqueous liquid, solid) and the concept of thermal shock as a sudden temperature change.
- Heating/cooling procedures: Prescribes stepwise heating/cooling when intended changes exceed diagram limits (example: staged steam pressure increases to raise product temperature).
- Design and material conditions: Limits assume apparatus designed per Part 1 and use of unalloyed or low-alloy carbon steel with a minimum yield strength around 210 N/mm² (Annex A).
- Allowances and agreements: If heat-transfer coefficients are low (e.g., viscous products or non-condensing heating media), wider thermal shock limits may be agreed between manufacturer and user.
- Quality designation: Items conforming to Part 3 should be designated as “Resistance to thermal shock in accordance with ISO 28721-3.”
Practical applications
- Specifies safe operating and commissioning practices for glass-lined reactors, vessels, heat-exchangers and piping used in chemical process plants, pharmaceuticals, food processing and similar industries where enamel protection is used to resist corrosion.
- Helps designers and plant engineers determine permissible product charging and jacket heating/cooling strategies to avoid enamel cracking or delamination.
- Guides manufacturers, inspection and QA teams on acceptance criteria and labelling for thermal shock resistance of glass-lined steel equipment.
Who should use this standard
- Process engineers and mechanical designers specifying glass-lined apparatus
- Equipment manufacturers and enamellers of glass-lined steel
- Maintenance, commissioning and QA teams in chemical and process industries
- Procurement and compliance professionals writing technical specifications
Related standards
Keywords: EN ISO 28721-3:2011, thermal shock resistance, glass-lined apparatus, vitreous and porcelain enamels, glass-lined steel, process plants, heating and cooling procedures, chemical plant equipment.
