Overview
ISO 17474:2012 establishes clear conventions for reporting and displaying electrochemical corrosion data. It standardizes sign conventions, plotting formats and units for common electrochemical measurements used in corrosion testing - including electrode potential, current density, polarization curves and electrochemical impedance data (EIS). The goal is to make results comparable between laboratories and over time by prescribing how data are presented graphically and numerically.
Key Topics
- Sign conventions
- Positive electrode potential = more oxidizing / noble direction; negative = more reducing / active direction.
- Current/current density: anodic positive, cathodic negative (absolute values may be plotted on log scales with clear differentiation).
- Polarization data
- Recommended axes: current density (ordinate, y) vs potential (abscissa, x).
- Use logarithmic scales for wide current ranges (Tafel analysis) or linear scales for small ranges and polarization resistance (Rp) determination.
- Polarization resistance (Rp) defined from the slope of potential vs current density at the corrosion potential (Ecorr); Rp relates to corrosion current and Tafel slopes.
- Reference electrode and potential reporting
- Always indicate the reference electrode used and, where practical, provide conversion to the Standard Hydrogen Electrode (SHE) (example provided in the standard: E vs SHE = E vs 1M KCl/AgCl/Ag + 0.235 V).
- Units
- Potential: V (or mV, µV for small ranges).
- Current density: A·m⁻² or A·cm⁻² (mA·cm⁻², µA·cm⁻² commonly used).
- Impedance: Ω·cm² (impedance multiplied by exposed area).
- Electrochemical impedance conventions
- Definitions: Z = Re(Z) + j·Im(Z); |Z| = sqrt[Re² + Im²]; phase θ = −arctan(Im/Re).
- Nyquist plot: real (Re Z) on x-axis, negative imaginary (−Im Z) on y-axis; frequency not explicit but can be annotated.
- Bode plot: log frequency (x-axis) vs log |Z| and phase (y-axis).
Applications and Who Uses It
ISO 17474 is intended for:
- Corrosion engineers, materials scientists and electrochemists performing potentiostatic, potentiodynamic, open-circuit potential, galvanic and EIS tests.
- Testing laboratories and quality assurance teams needing consistent reporting for inter-lab comparison and regulatory submissions.
- R&D and failure analysis groups interpreting polarization behavior, passive film properties, and impedance spectra.
Practical benefits include clearer communication of EIS/Nyquist/Bode data, consistent plotting of polarization curves, and unambiguous reporting of reference electrodes and units.
Related Standards
- ISO 8044 - Corrosion of metals and alloys: basic terms and definitions (normative reference).
- Methodological origins referenced from ASTM G3 practices for electrochemical measurements (see ISO 17474 introduction).
Keywords: ISO 17474, electrochemical corrosion, electrode potential, current density, polarization curves, polarization resistance, electrochemical impedance spectroscopy, Nyquist plot, Bode plot, reference electrode, SHE.
Open preview (PDF)Corrosion of metals and alloys — Conventions applicable to electrochemical measurements in corrosion testing
