ISO 28721-2:2025 PDF

Vitreous and porcelain enamels — Glass-lined apparatus for process plants — Part 2: Designation and specification of resistance to chemical attack and thermal shock

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Title (English):

ISO 28721-2:2025

Vitreous and porcelain enamels — Glass-lined apparatus for process plants — Part 2: Designation and specification of resistance to chemical attack and thermal shock

Document status:: Active
Format:: Electronic (PDF)
Number of pages:: 3
Publication date:: February 12, 2025
Edition:: ISO IS 28721 edition 3 version 1
ICS:: 25.220.50

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Description (English):

This document specifies requirements for the resistance of chemical enamels to chemical attack and thermal shock, as well as their designation, for ordering purposes. It is applicable to enamels used in glass-lined apparatus, piping and other components, primarily used in process equipment in chemical plants, which are applied on to low-alloy carbon steels substrates. NOTE The main criteria for assessing enamel quality are its resistance to chemical attack and thermal shock, and the structure of the cover coat enamel.

Technical details

Technical committee: ISO/TC 107 - Metallic and other inorganic coatings
SKU: ISO 28721-2:2025

Abstract

Overview

ISO 28721-2:2025 specifies how to designate and specify the resistance of vitreous and porcelain enamels used on glass-lined apparatus for process plants to chemical attack and thermal shock. The standard applies to enamels applied to low-alloy carbon steel substrates in chemical plant equipment and defines measurable quality criteria for ordering, testing and acceptance.

Key topics and requirements

Designation for ordering: Enamel quality shall be specified in terms of measurable resistance parameters (corrosion rates, crack formation temperature), cover-coat structure and colour.
Chemical corrosion limits:
- Resistance to condensing hydrochloric acid vapour: corrosion rate ≤ 0.08 mm/year (per ISO 28706-2).
- Resistance in 0.1 mol/L sodium hydroxide (NaOH) at 80 °C for 24 h: corrosion rate ≤ 0.40 mm/year with a specified volume/surface ratio (per ISO 28706-4).
Thermal shock / crack formation temperature:
- Crack formation temperature (per ISO 13807) shall be ≥ 190 °C for primary equipment.
- For accessories (agitators, baffles, thermometer wells, immersion tubes, sensors, piping accessories, pumps) a minimum of 170 °C may be permissible.
Cover-coat structure: Classification examples include all-vitreous, all-semicrystalline, vitreous over semicrystalline, or semicrystalline over vitreous.
Normative references: ISO 13807, ISO 19496-1, ISO 28706-2, ISO 28706-4 are referenced for test methods and terminology.

Applications

Specifying enamel performance for glass-lined reactors, piping, vessels, and accessories in the chemical and process industries.
Creating procurement and inspection criteria for manufacturers, fabricators and suppliers of glass-lined apparatus.
Defining acceptance criteria used by testing laboratories and quality assurance teams to verify resistance to chemical attack and thermal shock.
Guiding material selection in corrosive or thermally cycling environments where long-term enamel integrity is critical.

Who uses this standard

Chemical plant engineers and process designers
Procurement and specification writers for industrial equipment
Manufacturers of glass-lined equipment and enamel formulators
QA/QC inspectors and independent testing labs
Regulatory/compliance teams and asset integrity managers

Related standards

ISO 28721-1 / ISO 28721-3 (other parts of the series - see ISO 28721-3 for thermal shock resistance specifics)
ISO 13807, ISO 28706-2, ISO 28706-4, ISO 19496-1 (test methods and terminology)

Keywords: ISO 28721-2, glass-lined apparatus, vitreous enamel, porcelain enamel, chemical attack resistance, thermal shock, crack formation temperature, corrosion rate, process plants.

Related standards

Standards mentioned in the description

Abstract

Overview

Key topics and requirements

Designation for ordering: Enamel quality shall be specified in terms of measurable resistance parameters (corrosion rates, crack formation temperature), cover-coat structure and colour.
Chemical corrosion limits:
- Resistance to condensing hydrochloric acid vapour: corrosion rate ≤ 0.08 mm/year (per ISO 28706-2).
- Resistance in 0.1 mol/L sodium hydroxide (NaOH) at 80 °C for 24 h: corrosion rate ≤ 0.40 mm/year with a specified volume/surface ratio (per ISO 28706-4).
Thermal shock / crack formation temperature:
- Crack formation temperature (per ISO 13807) shall be ≥ 190 °C for primary equipment.
- For accessories (agitators, baffles, thermometer wells, immersion tubes, sensors, piping accessories, pumps) a minimum of 170 °C may be permissible.
Cover-coat structure: Classification examples include all-vitreous, all-semicrystalline, vitreous over semicrystalline, or semicrystalline over vitreous.
Normative references: ISO 13807, ISO 19496-1, ISO 28706-2, ISO 28706-4 are referenced for test methods and terminology.

Applications

Specifying enamel performance for glass-lined reactors, piping, vessels, and accessories in the chemical and process industries.
Creating procurement and inspection criteria for manufacturers, fabricators and suppliers of glass-lined apparatus.
Defining acceptance criteria used by testing laboratories and quality assurance teams to verify resistance to chemical attack and thermal shock.
Guiding material selection in corrosive or thermally cycling environments where long-term enamel integrity is critical.

Who uses this standard

Chemical plant engineers and process designers
Procurement and specification writers for industrial equipment
Manufacturers of glass-lined equipment and enamel formulators
QA/QC inspectors and independent testing labs
Regulatory/compliance teams and asset integrity managers

Related standards

ISO 28721-1 / ISO 28721-3 (other parts of the series - see ISO 28721-3 for thermal shock resistance specifics)
ISO 13807, ISO 28706-2, ISO 28706-4, ISO 19496-1 (test methods and terminology)

Keywords: ISO 28721-2, glass-lined apparatus, vitreous enamel, porcelain enamel, chemical attack resistance, thermal shock, crack formation temperature, corrosion rate, process plants.

ISO 28721-2:2025 PDF

Technical details

Abstract

Overview

Key topics and requirements

Applications

Who uses this standard

Related standards

Related standards

Abstract

Overview

Key topics and requirements

Applications

Who uses this standard

Related standards

Related standards

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