Overview
ISO 4628-8:2012 specifies a reproducible method to assess delamination and corrosion around a scribe or other artificial defect on coated panels or test specimens exposed to a corrosive environment. The standard is part of the ISO 4628 series for evaluation of coating degradation and focuses on measurement-and-calculation procedures (with optional pictorial standards) to quantify the extent of coating lift-off (delamination) and corroded area adjacent to deliberately introduced holidays. NOTE: ISO 4628-8 does not cover pitting corrosion or pit depth.
Key topics and technical requirements
- Scope and purpose: Evaluation of delamination and corrosion caused by corrosive atmospheres (e.g., salt spray, sea water immersion, or natural environments).
- Artificial defects: Linear scribes or circular/other shaped artificial holidays intentionally introduced to expose substrate.
- Timing of assessment: Delamination assessed immediately after exposure or after conditioning (commonly 24 h at 23 ± 2 °C and 50 ± 5 % RH per ISO 3270) when agreed. Corrosion can be evaluated on the coated panel or after stripping the coating.
- Minimum sampling: Testing of at least three replicate panels unless otherwise specified or agreed.
- Measurement method: Widths of delamination/corrosion measured at a minimum of six points uniformly distributed along the scribe or around the defect, to the nearest 0.5 mm (magnification allowed). Non‑uniform cases can use area-based calculations. The standard provides formulas to calculate the mean overall width based on these measurements or on measured delaminated/corroded areas.
- Removal and inspection: Loose coating removed carefully (knife, tape, paint remover) before measurement; when stripping is used, panels are rinsed and sealed with clear lacquer prior to area measurement.
- Optional pictorial standards: Parties may agree to use pictorial grading; however measurement and calculation are preferred.
- Reporting: Test report must identify coating details, test conditions (duration, corrosive environment), scribe/defect geometry and method, individual results and means, deviations, anomalies and test date.
Applications and users
ISO 4628-8 is used for:
- Coating manufacturers for product development and quality control.
- Independent test laboratories performing corrosion resistance tests (salt spray, immersion).
- Corrosion and materials engineers assessing system performance and failure modes.
- Specification writers and QA/QC teams who require objective, repeatable metrics for delamination and corrosion adjacent to holidays.
Keywords: ISO 4628-8, delamination, corrosion around a scribe, paint testing, coating evaluation, salt spray, coated panels, artificial defect, measurement and calculation.
Related standards
- ISO 4628-1 (general designation system) and other ISO 4628 parts (blistering, rusting, cracking, flaking, chalking, filiform corrosion).
- ISO 3270 (conditioning temperatures/humidities).
- Test environment references: ISO 9227 (salt spray) and ISO 15711 (sea water immersion).