Overview
EN ISO 21227-3:2007 (ISO 21227-3:2007) defines a digital optical imaging method for the objective evaluation of delamination and corrosion around a scribe on coated surfaces. It specifies how to capture, calibrate and analyse digital images of test panels (e.g., scribe tests produced according to ISO 9227, ISO 11997-1 or ISO 11997-2) to determine damaged area, mean and maximum widths and the shape of the affected zone. The method is intended to be more quantitative, reproducible and precise than traditional visual (pictorial) assessments.
Key topics and requirements
- Scope: Evaluation of delamination and corrosion around a scribe using digital optical imaging.
- Imaging & illumination:
- Use illumination that clearly distinguishes damaged from undamaged areas.
- Diffused reflection is preferred for corrosion (after stripping); directional reflection may help detect delamination without removing the coating.
- Resolution: Minimum imaging resolution of 6 pixels per millimetre; deviations must be reported.
- Calibration: Calibrate scale in both X and Y (e.g., graph paper or pictorial standards) so area and width measurements are accurate.
- Procedure:
- Prepare panels per ISO 4628-8.
- Capture calibrated images of the scribe region, threshold to a binary image, and measure damaged area (including the scribe).
- Determine scribe length and, if required, scribe width.
- Evaluation outputs:
- Damaged area, mean delamination width and mean corrosion width (derived from measured areas and scribe length), maximum widths and the delamination/corrosion shape.
- Results can be converted to the numerical rating scale (0–5) of ISO 4628-8 for comparability with visual assessment.
- Precision: Interlaboratory data showed ~9% relative standard deviation for digital mean-width determinations (visual assessments exhibited higher variability).
Practical applications
- Quality control and acceptance testing in coatings manufacturing and automotive, marine and industrial sectors.
- R&D and failure analysis to quantify adhesion loss and corrosion propagation around defects.
- Contract and regulatory testing where objective, reproducible metrics (area, mean width, shape) are required instead of subjective visual grades.
- Interlaboratory comparisons and calibration of imaging systems for coating performance evaluation.
Who should use this standard
- Coating test laboratories, materials engineers, corrosion specialists, quality assurance teams, and standards bodies involved in paints and varnishes testing.
Related standards
Keywords: EN ISO 21227-3:2007, ISO 21227-3, paints and varnishes, delamination, corrosion, optical imaging, digital image analysis, scribe test, coated surfaces, evaluation of defects.