Overview
ISO 4628-3:2024 - Paints and varnishes: Assessment of degree of rusting - specifies visual methods for assessing rust on coated surfaces. It covers evaluation of red rust (ferrous substrates) and white rust (non‑ferrous/zinc substrates or duplex systems) by comparison with pictorial standards and by estimating the corroded area in percent. The standard applies to organic coatings and metallic coatings plus an organic topcoat (duplex systems). Edges of specimens are excluded from the assessment.
Key SEO terms: ISO 4628-3:2024, rusting assessment, pictorial standards, red rust, white rust, corroded area, coatings.
Key topics and technical requirements
- Two assessment methods
- Method 1 (Ri / WRi): Compare the test surface with pictorial standards (Figures 1–5 for red rust; Figures 6–10 for white rust). Calibration images are provided (Annex A) for optical systems.
- Method 2 (R% / WR%): Estimate the corroded area as a percentage and rank it against the tabled ranges (0, up to 5 %, >5–10 %, >10–25 %, >25–50 %, >50 %).
- Size classification for rust spots (S0–S5) is provided (Table 1) to indicate average spot dimensions when they differ from pictorial examples.
- Inspection conditions: Assessments must be made under suitable illumination as specified in ISO 13076. Rust traces from bleeding are excluded.
- Reporting: Results shall specify the degree (Ri/WRi or R%/WR%), and which assessment method was used. Annex B gives an example panel after NSS (neutral salt spray) testing.
- Scope limits: The assessment is an estimation of affected area on the specimen surface; edges are not included.
Practical applications and users
ISO 4628-3:2024 is used to:
- Standardize visual evaluation of rust in quality control for coating manufacturers.
- Provide acceptance criteria and inspection procedures for coating contractors and fabricators.
- Support corrosion testing laboratories and R&D teams evaluating formulations or protective systems (including NSS salt spray testing per ISO 9227 examples).
- Inform spec writers, procurement, and maintenance engineers for conformity and warranty claims.
Benefits:
- Enables consistent communication of rust performance across suppliers, labs and clients.
- Provides a visual, reproducible method for pass/fail decisions and trend analysis.
Related standards
- ISO 4628 series (general defect designation)
- ISO 4618 (paints and varnishes - vocabulary)
- ISO 13076 (lighting and procedure for visual assessments)
- ISO 9227 (neutral salt spray testing) - example panels referenced in Annex B
- Correlation to ASTM D610‑08 is discussed in Annex C
Use ISO 4628-3:2024 when you need a standardized, visual, and percentage-based method to assess and report the degree of rusting on coated surfaces.
Open preview (PDF)Paints and varnishes — Evaluation of quantity and size of defects, and of intensity of uniform changes in appearance — Part 3: Assessment of degree of rusting