Overview
ISO 28723:2008 is an international standard that specifies a precise test method for determining the edge covering of vitreous and porcelain enamel coatings on steel plates used in heat exchangers. This standard applies to enamelled steel plates with thicknesses ranging from 0.5 mm to 1.5 mm and covers all enamelling processes. The determination of edge coverage ensures the durability and corrosion resistance of enamel coatings vital for heat exchanger performance. The test is based on measuring the electrical current that flows when the enamelled plate edge is immersed in an electrolyte solution, correlating to the enamel’s edge coverage quality.
Key Topics
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Scope and Applicability
The method applies to enamelled steel plates intended for heat exchangers, notably those 0.5 to 1.5 mm thick. It excludes tests where current flow exceeds 3 A.
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Test Principle
The enamelled plate’s edge is immersed in an electrolyte, such as a sodium chloride solution, and connected to an alternating current source. The intensity of current measured is directly proportional to the extent of non-covered, bare steel on the edge of the plate.
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Reagents and Materials
Analytical grade reagents and distilled or demineralized water are prescribed, ensuring consistent and reliable results. Critical reagents include a 7% sulfuric acid pickling solution with iron concentration and a 5% sodium chloride test electrolyte.
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Test Equipment
The apparatus includes a polypropylene test bath, stainless steel electrodes (compliant with EN 10088-1), a stabilized AC voltage source delivering 10V ±0.05, and a sensitive ammeter capable of measuring current with 0.01 A accuracy.
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Procedure
Plates are pretreated in acid solution, rinsed, and dried before immersion in the electrolyte bath. The edge covering is quantified by measuring the current flowing through the plate edge immersed up to 10 mm into the electrolyte.
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Calculations and Results Expression
The method provides equations to calculate the non-covered surface area of the enamel edge and express results as a percentage of edge coverage and surface area of uncovered steel per meter length. The precision of measurement is ±0.3% for edge coverage percentage.
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Test Report Requirements
Detailed reporting requirements ensure traceability and reproducibility, covering sample identification, adherence to ISO 28723:2008, measurement values, any deviations from procedures, observed anomalies, and testing dates.
Applications
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Heat Exchanger Manufacturing
Ensuring enamel coatings on steel plate edges meet strict quality criteria is critical for the corrosion resistance and thermal efficiency of heat exchangers.
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Quality Control in Enamelling Processes
ISO 28723:2008 provides manufacturers with a reliable method for confirming enamel application integrity at edges, a common failure point.
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Material Certification
This test supports certification processes, helping steel enamel producers validate their products against international quality expectations.
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Research and Development
Insight into edge coating coverage facilitates improvements in enamelling technology and materials used in heat exchangers.
Related Standards
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ISO 3696 - Water for Analytical Laboratory Use
Defines the quality requirements for water used in testing to ensure contamination does not affect the electrochemical measurements.
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EN 10088-1 - Stainless Steels
Specifies stainless steel grades used for electrodes in the electrolyte bath, ensuring consistent electrode performance.
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ISO/IEC Directives Part 2 - Principles for International Standard Development
Governs the structure and drafting of ISO standards including ISO 28723:2008.
Practical Value
Compliance with ISO 28723:2008 ensures that enamelled steel plates used in heat exchangers have appropriate edge coverage, directly impacting the lifespan and safety of heat exchanger equipment. The standardized test method enhances quality assurance, helps reduce maintenance costs, and supports manufacturers in meeting both customer and regulatory requirements. By following this method, industries can reliably assess enamel durability and prevent premature corrosion failures at critical plate edges.
Open preview (PDF)Vitreous and porcelain enamels — Determination of the edge covering on enamelled steel plate to be used in heat exchangers
