ISO 28721-2:2015

Overview

ISO 28721-2:2015 is an international standard that defines the requirements for vitreous and porcelain enamel coatings used in glass-lined apparatus for process plants. Specifically, this part focuses on the designation and specification of resistance to chemical attack and thermal shock of these enamel coatings. It applies primarily to enamelled equipment, piping, and components used in chemical process plants, fabricated from unalloyed and low-alloy carbon steels suitable for enamelling.

The standard ensures enamel quality by establishing minimum resistance criteria for chemical corrosion and thermal shock. This is critical as these parameters determine the durability, safety, and performance of glass-lined apparatus exposed to harsh chemical environments and temperature fluctuations.

Key Topics

• Resistance to Chemical Attack
  • Measured by the rate of corrosion in specific aggressive media:
    • Hydrochloric acid vapour
    • Sodium hydroxide solution
  • Corrosion rates are standardized to maintain enamel integrity under process conditions.
• Thermal Shock Resistance
  • Characterized by the crack formation temperature of the enamel.
  • Ensures enamel withstands rapid temperature changes without cracking or degradation.
• Enamel Coating Structure
  • Classification includes all-vitreous, semicrystalline layers, or combinations thereof.
  • Structural characterization influences chemical and thermal resistance properties.
• Designation for Ordering
  • Enamel quality is designated based on:
    • Corrosion rates per standard test methods
    • Crack formation temperature
    • Cover coat enamel structure
    • Enamel colour, aiding identification and specification
• Applicable Materials
  • Only applies to unalloyed and low-alloy carbon steels suitable for enamelling to ensure standardization.

Applications

ISO 28721-2:2015 is essential for manufacturers, engineers, and operators of chemical process plants who rely on glass-lined apparatus for corrosion-resistant and thermally robust equipment. Common applications include:

• Chemical Reactors and Vessels: Ensuring long service life in acidic and alkaline environments.
• Piping and Fittings: Maintaining integrity in corrosive transport systems within process plants.
• Accessories: Including agitators, baffles, and instrumentation wells subject to chemical exposure and thermal cycling.
• Process Plant Equipment: Leveraging glass lining to protect steel substrates, reducing maintenance costs and downtime.

Adherence to this standard helps guarantee equipment performance, safety, and compliance with international best practices in process plant design and operation.

Related Standards

ISO 28721-2 is part of the broader ISO 28721 series addressing vitreous and porcelain enamels for glass-lined apparatus:

• ISO 28721-1: Quality requirements for enamelled apparatus, components, appliances, and accessories.
• ISO 28721-3: Detailed specifications on thermal shock resistance testing methods and acceptance criteria.
• ISO 28721-4: Quality requirements for glass-lined flanged steel pipes and fittings.
• ISO 28721-5: Presentation and characterization of defects in enamel coatings.

Additional referenced standards include:

• ISO 13807: Test method for determining crack formation temperature under thermal shock conditions.
• ISO 28706-2: Methods for determining chemical corrosion resistance in boiling acids and vapours.
• ISO 28706-4: Methods for chemical corrosion resistance in alkaline liquids.

Summary

Implementing ISO 28721-2:2015 provides manufacturers and end-users with a reliable framework to specify and verify the chemical corrosion resistance and thermal shock performance of enamel coatings on process equipment. This ensures optimized durability and safety of glass-lined apparatus in demanding chemical processing environments. By standardizing enamel quality designation, the standard facilitates clear communication, quality assurance, and regulatory compliance across the global chemical industry.