Overview
EN ISO 2746:2015 - "Vitreous and porcelain enamels - High voltage test" (adopted by CEN) defines two high-voltage test methods for assessing enamel coatings on metallic substrates. The standard covers both Test A (detection and location of defects that reach the metal base) and Test B (detection of defects and weak spots). Tests use DC or pulsed DC high voltage applied to dry enamel surfaces to generate optical/acoustic signals at spark events; Test A is typically non‑destructive, Test B can be destructive.
Key topics and requirements
- Test purposes
- Test A: Locate defects (e.g., open pores, cracks) that expose the metal base; generally applied to thin coatings.
- Test B: Locate defects and detect weak spots (blisters, inclusions, spalling) by higher voltages; typically applied to thick coatings and may create open pores.
- Voltage and dependence on coating thickness
- Test voltages depend on enamel coating thickness; the standard provides DC voltage guidance (Table 1) and allows agreed voltages for pulsed DC.
- Test A may be unsuitable when coating thickness varies widely.
- Apparatus and electrical parameters
- High-voltage generator (DC or pulsed DC) with specified accuracy and safety characteristics. For DC generators, internal resistance and current limits are specified (short-circuit mean current 2–3 mA max; spark peak 10–50 mA; charge per impulse ≤25 μC).
- Earthing/grounding: negative pole to earth/ground; positive to test electrode via screened cable.
- Test electrode options: metal wire or conductive rubber; brush holder and insulated hand-piece with earthed cover are specified.
- Indicator device for optical/acoustic detection and coating thickness measurement (referenced ISO 2178 / ISO 2360).
- Test conditions & limitations
- Applicable to dry surfaces; moist surfaces require care to correctly locate defects.
- Edges/borders within 2 cm can produce arcing and may be unsuitable for testing.
- Safety note: standard does not cover health/safety requirements - follow relevant regulations and IEC/TS 60479 guidance on effects of current on humans and livestock.
Applications and users
- Quality control and inspection of enamelled products: sinks, cookware, architectural panels, chemical industry vessels, storage tanks.
- Coating manufacturers and enamel applicators for process monitoring and defect-density measurement.
- Laboratories and certification bodies verifying enamel dielectric performance or resistance under corrosive conditions.
- Design/specification engineers writing procurement or acceptance criteria for enamel coatings.
Related standards
- ISO 2178 - coating thickness measurement (magnetic method)
- ISO 2360 - coating thickness measurement (eddy-current method)
- IEC/TS 60479-1 / 60479-2 - effects of electric current on humans/livestock (safety guidance)
- EN 14430:2004 - superseded by EN ISO 2746:2015
Keywords: EN ISO 2746:2015, high voltage test, vitreous and porcelain enamels, Test A, Test B, DC, pulsed DC, coating thickness, enamel defect detection.
