Overview
ISO 8502-5:1998 specifies a field test method for measuring soluble chloride ions on steel surfaces prepared for painting using ion detection tubes. It is part of the ISO 8502 series for assessing surface cleanliness prior to paint application. The method is intended for use on steel surfaces before and after cleaning and on painted surfaces between coats to help prevent coating failure and corrosion caused by residual chlorides.
Key topics and requirements
- Test principle: Controlled washing (swabbing) of a defined test area to extract water‑soluble chlorides; analysis of the wash solution using silver chromate ion detection tubes that indicate chloride concentration by a colour change.
- Sampling procedure: Mark and wash a 0.25 m² (0.5 m × 0.5 m) test area by repeated swabbing with chloride‑free gauze, collect washings in a beaker, and combine rinse water as specified.
- Apparatus and materials: Grade 3 water (ISO 3696), calibrated chloride ion detection tubes (borosilicate tube filled with 5% silver chromate in silica sand), cutter, beakers, measuring cylinder, cotton gauze, gloves, tape and measuring tools.
- Analysis and reporting: Use five fresh detection tubes, record individual readings and the average of the three middle values. Verify tube calibration with a known chloride solution; verification accuracy ±15%. Recommended verification concentration range: 50–100 mg/l.
- Calculation: Convert chloride concentration (mg/l) and extraction volume to surface chloride expressed as mg NaCl/m² using the molecular mass ratio and test area.
- Environmental/measurement limits: Test valid between 5 °C and 80 °C (do not perform below 5 °C). Note common interferences (bromide/iodide/cyanide produce slightly higher readings; sulfate, nitrate or iron may affect results up to ~10%; pH 4–13 generally not affecting results).
Practical applications and users
- Who uses it: Coatings inspectors, corrosion engineers, paint specifiers, surface preparation contractors, maintenance teams and quality control laboratories performing on-site assessment of surface cleanliness.
- When to use: Pre-paint inspection, verification of cleaning effectiveness, assessment between coating layers, and routine maintenance checks on bridges, ships, offshore structures, tanks and industrial steelwork.
- Benefits: Rapid on-site chloride detection, helps prevent premature coating failure and corrosion, supports compliance with painting specifications and contract acceptance criteria.
Related standards
- ISO 8502 (series) - surface cleanliness tests (Parts 1, 2, 3, 4, 6, 8, 9, 10 referenced in the ISO 8502 foreword)
- ISO 8502-2 - laboratory determination of chloride on cleaned surfaces
- ISO 8502-6 - Bresle method for extraction of soluble contaminants
- ISO 3696 - water for analytical laboratory use
Keywords: ISO 8502-5, chloride measurement, ion detection tube, surface cleanliness, steel substrate preparation, pre-paint inspection, Bresle method, field test for chlorides.
Open preview (PDF)Preparation of steel substrates before application of paints and related products — Tests for the assessment of surface cleanliness — Part 5: Measurement of chloride on steel surfaces prepared for painting (ion detection tube method)