Overview
EN ISO 4623-1:2018 - Paints and varnishes - Determination of resistance to filiform corrosion - Part 1: Steel substrates (ISO 4623-1:2018) specifies a standardized test method for assessing how coatings on steel resist filiform corrosion initiated from a deliberately scribed break in the coating. The procedure is published by ISO and endorsed as a CEN (European) standard and is intended for laboratory evaluation of a specific coating/substrate combination - it is not a predictive method for different substrates or field life.
Key topics and technical requirements
- Scope: Tests protective action of paints/varnishes on steel against filiform corrosion starting from a scribe mark cut through the coating.
- Principle: A coated test panel is scribed; a small amount of sodium chloride is introduced into the scribe (by dipping or by salt-fog exposure); panels are then exposed in a test cabinet at 40 °C and 80% relative humidity to encourage filamentous corrosion growth.
- Salt introduction: Two accepted techniques - dipping in NaCl solution or exposure to neutral salt fog. (The 2018 edition shortened neutral salt-fog exposure from 24 h to 4 h.)
- Inspection & evaluation: Results are assessed after exposure using mutually agreed criteria - either subjective assessment or standardized assessment such as ISO 4628‑10. Filiform corrosion is recorded when thread‑like patterns develop from the scribe.
- Limitations: Results apply only to the tested coating/substrate pair; environmental parameters (temperature, humidity) strongly affect outcomes and must be controlled and reported.
Practical applications and users
Who uses EN ISO 4623-1:2018:
- Coating manufacturers and formulators validating antifiliform performance on steel
- Independent testing laboratories performing corrosion resistance testing
- Quality assurance and R&D teams in automotive, marine, infrastructure, and industrial coatings
- Specifiers and procurement teams requiring standardized performance evidence for coated steel components
Practical uses:
- Comparative performance testing of coating systems on steel substrates
- Quality control of production batches or new formulations
- Supporting technical data sheets and warranty claims where filiform resistance is relevant
Related standards
Standards commonly referenced alongside EN ISO 4623-1:2018:
Using EN ISO 4623-1:2018 helps ensure consistent, repeatable laboratory assessment of filiform corrosion resistance for paints and varnishes on steel, supporting product development, specification compliance, and quality assurance.
