Overview
ISO 22410:2020 specifies an electrochemical method to evaluate the protective quality of rust (patina) formed on weathering steel. The standard defines how to measure the ion transfer resistance of the rust layer using electrochemical AC impedance combined with harmonic analysis, together with rust thickness measurements, to assess whether the rust provides effective long‑term corrosion protection.
Key topics and technical requirements
- Purpose: Quantitative, largely non‑destructive assessment of the rust layer’s ability to impede ionic transport and thus protect the steel substrate.
- Measurement techniques:
- Electrochemical impedance spectroscopy (EIS) coupled with harmonic current analysis to separate ion transfer resistance from capacitive effects.
- Rust thickness measurement (commonly by electromagnetic devices) to characterize layer stability.
- Laboratory setup:
- Conventional three‑electrode arrangement with an Ag/AgCl reference electrode.
- Typical electrolyte: 0.1 M Na2SO4 solution, open to air (used because it minimally alters rust during short tests).
- Potentiostat and frequency response analyzer controlled by a computer.
- Data interpretation:
- Identification of three frequency regions (low, mid, high) in impedance/harmonic spectra:
- Low frequency: pseudo‑capacitive behavior and higher‑order harmonic currents (charge‑transfer processes).
- Mid frequency: pseudo‑resistive region where impedance is nearly frequency‑independent-used to determine rust layer (ion transfer) resistance.
- High frequency: additional pseudo‑capacitance associated with the rust layer.
- Use of equivalent electrical circuits (solution resistance, ion transfer resistance, polarization resistance, rust and double‑layer capacitances) to model the system.
- Field practice: Portable double‑probe instruments are referenced for in‑situ monitoring of existing structures.
Applications and who should use it
ISO 22410:2020 is directly applicable for:
- Corrosion and materials engineers assessing weathering steel bridges, towers and structures.
- Testing laboratories performing EIS and harmonic analysis on aged steel.
- Asset managers and inspection teams evaluating maintenance needs and life‑cycle performance of weathering steel.
- Researchers developing non‑destructive monitoring protocols for atmospheric corrosion.
Practical outcomes include condition mapping, verification of protective patina formation, and decision support for maintenance or remediation.
Related standards
- ISO 2178 - Measurement of coating thickness (magnetic method) - relevant for rust/coating thickness techniques.
- ISO 9223 - Classification and determination of atmospheric corrosivity - useful for contextualizing exposure conditions.
Keywords: ISO 22410:2020, weathering steel, ion transfer resistance, electrochemical impedance, harmonic analysis, rust layer thickness, corrosion protection, non‑destructive monitoring.