Overview
ISO 4623-1:2018 specifies a laboratory test method to assess the resistance of paints and varnishes on steel substrates to filiform corrosion initiated from a scribed break in the coating. The procedure evaluates the protective action of a specific coating/substrate combination by deliberately introducing chloride at a scribe and exposing the panel under controlled temperature and humidity. Results are only valid for the tested combination and are not predictive for different substrates.
Key topics and technical requirements
- Scope & limitation: Designed for coated steel test panels; results apply only to the tested coating/substrate pair.
- Test principle: Create defined scribe(s) through the coating, introduce sodium chloride by dipping or salt fog, then expose panels at 40 °C and 80 % relative humidity to encourage filiform corrosion growth.
- Test panels: Ground steel panels per ISO 1514, minimum size 150 × 75 × 0.3 mm; back and edges coated; coating thickness measured per ISO 2808.
- Scribing: Two perpendicular scribes at least 30 mm long; cutting edge must fully penetrate the coating; use a mechanical scribing device where possible and verify metal visibility at ×10 magnification.
- Initiation techniques:
- Dipping: Immerse scribed panel in 1 g/L NaCl solution for 30–60 s, remove excess drops, place in the test cabinet; repeat every 3–4 days as specified.
- Salt fog: Expose to neutral salt fog per ISO 9227; for durable systems salt fog exposure usually does not exceed 4 h.
- Exposure conditions: Test cabinet maintained at (40 ± 2) °C and (80 ± 5) % RH. If automatic control is unavailable, a saturated ammonium sulfate solution provides ~79 % RH at 40 °C (guidance in Annex A).
- Evaluation & reporting: Assess filiform corrosion extent using agreed criteria or ISO 4628-10; perform tests in duplicate and report sampling, conditioning (ISO 3270), apparatus, scribe method, exposure cycles, and measured coating thickness.
Applications and users
ISO 4623-1 is used for:
- Quality control and batch acceptance testing of industrial, marine, and automotive coatings on steel
- Product development and comparative performance testing
- Failure analysis and warranty evaluations involving filiform corrosion
Primary users include coatings manufacturers, independent test laboratories, corrosion engineers, specification writers, and procurement teams.
Related standards
Keywords: ISO 4623-1, filiform corrosion, paint testing, steel substrates, coating performance, salt fog, dipping technique, scribing, test cabinet, corrosion resistance.
Open preview (PDF)Paints and varnishes — Determination of resistance to filiform corrosion — Part 1: Steel substrates