Overview
ISO 8502-2:2017 specifies a laboratory method to determine water‑soluble chloride contamination on steel substrates prior to painting. The standard covers a practical swabbing/wash‑off procedure (applicable in the field or laboratory) and refers to several analytical techniques for measuring chloride in the collected wash‑water. ISO 8502-2 is part of the ISO 8500 series on surface cleanliness for paint performance and corrosion control.
Key topics and requirements
- Scope: Targets chloride‑containing salts that are readily soluble in water; applicable to bare and previously coated steel surfaces. It provides a wash‑off sampling technique and guidance on analytical options.
- Sampling procedure:
- Mark a test area (example: ~25 000 mm² - e.g., 250 mm × 100 mm) and record the actual area.
- Use ~45 ml of high‑purity water to soak absorbent pads and thoroughly swab the area; collect washings and filter into a 50 ml volumetric flask.
- Swabbing should take at least 10 minutes and tests are carried out in duplicate.
- Analytical methods (selection referenced in the standard):
- Ion chromatography (ISO 10304-1)
- Ion detection tubes (ISO 8502-5)
- Ion‑selective electrode (ISO 9517)
- Coulometric titration (informative Annex A)
- Conductivity conversion (ISO 8502-9) when non‑specific assessment is acceptable
- Result expression: Calculate chloride mass per area (mg/m²) from measured chloride concentration, sample volume and test area (formula provided in Clause 7). Account for any dilutions or conditioning steps.
- Limitations: Method measures only readily water‑soluble chloride removed by the wash; it does not represent total chloride trapped in crevices, pits or beneath corrosion films. Measurement uncertainty must be reported.
- Reporting: Test reports must identify the surface, method used, individual and mean results, deviations, anomalies and test dates.
Applications and users
ISO 8502-2 is used to assess surface cleanliness to reduce coating failure and corrosion risks. Typical use cases:
- Coating specifiers and engineers verifying pre‑treatment requirements for bridges, ships, offshore structures, storage tanks and industrial plants.
- Inspection and quality control teams performing acceptance tests before painting.
- Laboratory analysts selecting and validating chloride analysis methods.
- Contractors and maintenance teams monitoring cleaning effectiveness and compliance with coating system requirements.
Related standards
Keywords: ISO 8502-2, chloride determination, surface cleanliness, steel substrates, wash-water analysis, pre-paint inspection, coating quality control, coulometric titration.