ISO 17475:2005

Overview

ISO 17475:2005 - "Corrosion of metals and alloys - Electrochemical test methods - Guidelines for conducting potentiostatic and potentiodynamic polarization measurements" - provides standardized guidance for performing electrochemical polarization tests on metals and alloys. The standard describes how to run potentiostatic (stepwise potential holding) and potentiodynamic (continuous potential scan) polarization measurements to characterise anodic and cathodic kinetics, the onset of localised corrosion (pitting, crevice, intergranular) and repassivation behaviour.

Key topics and requirements

• Test principle: Relates measured current to displacement from the open-circuit (free corrosion) potential to reveal anodic/cathodic kinetics and active–passive behaviour.
• Potentiostatic vs potentiodynamic: Defines step-hold potentiostatic testing and continuous-scan potentiodynamic testing, and explains the effects of hold time and scan rate on results.
• Apparatus and performance:
  • Potentiostat capability (example: control within ±1 mV) and scanning functions for potentiodynamic tests.
  • Instruments with adequate sensitivity (able to detect ~1 mV changes) and suitable current-measurement accuracy (document references 0.5 % max error as a guideline).
  • Test cell design: working electrode (test specimen), reference electrode, auxiliary (counter) electrode, Luggin capillary placement, inert cell materials and appropriate solution volume to avoid chemistry changes during testing.
• Reference and auxiliary electrodes: Selection and placement (including salt bridges, double junctions and Luggin capillaries) to minimize ohmic drop and contamination. Annex B gives common reference electrode potentials versus SHE at 25 °C.
• Specimen and solution preparation: Defined surface finish (e.g., Ra <1 µm recommended in many applications), controlled elapsed time after polishing, cleaning, and use of reagent-grade chemicals and high-purity water.
• Data interpretation cautions: Effects of scan rate, film formation, flow, temperature and solution conductivity on measured breakdown and repassivation potentials; ohmic drop compensation where needed.
• Validation and reporting: Calibration/validation of reference electrodes and reporting requirements for reproducibility.

Applications and users

ISO 17475 is used to:

• Compare corrosion resistance of metals and alloys under simulated service conditions.
• Determine breakdown (pitting/crevice) and repassivation potentials for material selection and qualification.
• Study electrochemical kinetics (exchange current, diffusion limitations) and evaluate protective coatings or inhibitors.
• Support failure analysis, R&D, quality control and regulatory compliance.

Typical users: corrosion engineers, materials scientists, metallurgists, laboratory technicians, research labs, coating and alloy developers, and standards bodies.

Related standards

• ISO 8044 - Corrosion: basic terms and definitions
• ISO 8407 - Removal of corrosion products from specimens
• ISO 11463 / ISO 9400 / ISO 11846 - Specific methods for pitting and intergranular corrosion assessment
• ASTM G5 and ASTM G150 - Related electrochemical polarization practice (informative references in ISO 17475)

Keywords: ISO 17475, corrosion testing, potentiostatic, potentiodynamic, polarization measurements, electrochemical test methods, pitting, repassivation, potentiostat, Luggin capillary.