ISO 4628-10:2024

Overview

ISO 4628-10:2024 - Paints and varnishes: Assessment of degree of filiform corrosion - specifies a standardized, repeatable method to evaluate filiform corrosion that develops from a scribed mark in coatings. The standard defines how to measure the length of the longest filament (L) and the most frequent filament length (M) (values in millimetres), and provides pictorial examples in Annex A to illustrate rating categories. The visual examples complement, but do not replace, the required numerical assessment carried out by Method 1 or Method 2.

Key topics and requirements

• Scope: Assessment of filiform corrosion developing from a scribe; numerical rating expressed as Lx/My (e.g., L5/M3).
• Definitions: Filiform corrosion defined in alignment with ISO 4623-1:2018 - corrosion under coatings in thread‑like growths initiated by aggressive ions.
• Assessment methods:
  • Method 1: For regular corrosion - measure maximum distances on left and right of the scribe to obtain mean longest filament (L) and most frequent length (M).
  • Method 2: For irregular corrosion - measure L and multiple M values across zones to calculate overall M using provided formulae.
• Measurement units: Distances recorded in millimetres.
• Visual aids: Annex A contains 12 pictorial examples mapping combinations of filament length (L1–L5) and filament frequency (M1–M5).
• Illumination: Assessments must be carried out under good lighting conditions as specified in ISO 13076.
• Test report content: Report shall include coating identification, reference to ISO 4628-10:2024, surface details, numerical result (Clause 5), illumination, whether coating was stripped, deviations, anomalies, and date.

Applications and users

ISO 4628-10:2024 is practical for:

• Quality control and inspection teams in coatings and corrosion laboratories
• Coating manufacturers and formulators validating product resistance to filiform corrosion
• Specifiers, asset owners and maintenance engineers assessing lifecycle performance of painted structures (e.g., marine, infrastructure, transportation)
• Certification bodies and testing laboratories preparing formal test reports

Using this standard supports objective, repeatable evaluation of coating failures caused by filiform corrosion and helps compare results across projects and suppliers.

Related standards

• ISO 4628-1 - General designation system for quantity/size of defects
• ISO 4623-1:2018 - Determination of resistance to filiform corrosion (steel substrates)
• ISO 13076 - Lighting and procedure for visual assessments of coatings

Keywords: ISO 4628-10:2024, filiform corrosion, paints and varnishes, coatings assessment, L and M ratings, evaluation of defects, coating inspection, corrosion testing.