Overview
EN ISO 28723:2011 (identical to ISO 28723:2008) defines a standardized test method for assessing the edge covering of enamelled steel plates intended for heat exchangers. The method measures the amount of uncoated (exposed) metal at the plate edge by immersing the edge in an electrolyte and recording a stabilized alternating current. The procedure is applicable to all enamelling processes for plates with a thickness from 0.5 mm to 1.5 mm and is not suitable where the test current exceeds 3 A.
Key topics and requirements
- Scope and applicability: Plates 0.5–1.5 mm thick; minimum tested edge length 300 mm; both corrugated and undulated specimens can be used.
- Principle: Submerge up to 10 mm of the plate edge in a 5 % NaCl electrolyte and apply a stabilized AC voltage. The measured current correlates with the uncoated edge area.
- Reagents & conditions:
- Pickling step in sulfuric acid (hot) prior to testing; rinse and dry.
- Test electrolyte: 5 % NaCl by mass, prepared with laboratory-grade water (ISO 3696 grade 3), at ~22 ± 3 °C.
- Apparatus:
- Polypropylene test bath with centring plates to position the specimen.
- Stainless-steel electrodes (EN 10088-1 grade 1.4301).
- Stabilized AC voltage source at 10.0 ± 0.05 V and an ammeter readable to 0.01 A.
- Procedure specifics:
- Immerse the prepared edge (max 10 mm immersion).
- Record current automatically 3 ± 0.5 s after switching on the voltage.
- Repeat for both edges and for paired specimens.
- Calculations & reporting:
- The standard provides the relationship between measured current and uncoated surface area, then calculates percentage free surface and percentage edge covering (E = 100 − S).
- Results expressed as mean percentage edge covering (nearest 0.1 %) and mean uncoated area per metre (nearest 10 mm²/m).
- Precision: stated measurement precision for edge covering and uncoated area.
Applications and users
- Manufacturers of enamelled steel plates and heat exchangers use EN ISO 28723 to validate edge quality and ensure corrosion protection at edges.
- Quality control laboratories perform routine compliance testing and provide contractual test reports.
- Design engineers and purchasers specify edge-covering acceptance criteria in procurement and performance standards.
- Useful for R&D when evaluating enamelling processes, coating uniformity, and edge-treatment methods.
Related standards
- ISO 3696 - water for laboratory use (referenced for test water quality)
- EN 10088-1 - stainless-steel grades (electrode material)
- EN 14863:2005 - superseded by EN ISO 28723:2011
Keywords: EN ISO 28723:2011, ISO 28723, edge covering, enamelled steel plate, heat exchangers, test method, NaCl electrolyte, percentage edge covering, quality control.
