Overview
ISO 8289-2:2019 specifies a low-voltage slurry (barbotine) test to detect and locate defects - pores, cracks or pop-offs - in vitreous and porcelain enamel coatings applied to corrugated or undulated (profiled) metal surfaces. The method is an optical, non-destructive low-voltage test that uses a conductive slurry and colour effects to indicate defects that extend down to the metal base.
The test is particularly suited to non-flat shapes (corrugated sheets, undulated profiles) where precise position mapping of defects is required.
Key Topics
- Principle: defects are revealed optically when a conducting slurry makes electrical contact between a positive electrode and exposed metal at the defect; a visible colour change (red spots in the slurry) marks each defect.
- Test medium: a sprayable, thixotropic slurry based on titanium dioxide, polysaccharide, pyrogenic silicic acid, quartz powder and an alcoholic phenolphthalein solution in a sodium chloride electrolyte. Typical slurry preparation details and proportions are given in the standard.
- Electrical parameters: the method uses a DC power source adjustable within approximately 10 V to 24 V; the routine test setting in the standard is 12 V for 1 minute.
- Solution characteristics: the test solution should have a conductivity of approximately 0.475 S/m (±0.025) and a pH ≈ 8 (±0.5). Sodium nitrite may be used as an alternative electrolyte when post-test re-enamelling is planned.
- Evaluation: defects are counted and reported as a number per unit area using N = S / A, where S is the number of defects detected and A is the test area in square metres.
Applications
- Quality control on enamelled heat-exchanger sheets, regenerative heat-exchanger components and other corrugated/undulated enamelled metal products.
- Incoming inspection, production-line spot checks and failure analysis where precise defect location and mapping are required without damaging the part.
- Useful for manufacturers, coating process engineers, QA laboratories and maintenance teams who need a repeatable, interpretable optical indication of coating breaches to the metal base.
Practical advantages:
- Non-destructive detection of defects that extend to the metal base
- Adapted to profiled, non-flat geometries where flat testers are impractical
- Produces visually locatable red spots for accurate defect positioning
Related Standards
- ISO 2746 - Vitreous and porcelain enamels: high-voltage test (contrasts with the low-voltage method)
- ISO 19496-1 - Terminology for vitreous and porcelain enamels
- EN 60086-2 - Primary batteries (referenced for battery selection when used as the power source)
For implementation, follow the specimen preparation, slurry formulation, apparatus and reporting clauses in ISO 8289-2:2019 and record results in the test report fields specified by the standard (reference, specimen ID, defects/m2, medium, date, operator).
Open preview (PDF)Vitreous and porcelain enamels — Low-voltage test for detecting and locating defects — Part 2: Slurry test for profiled surfaces
