Overview
ISO 15158:2014 defines a rapid electrochemical test method for measuring the pitting potential of stainless steels by potentiodynamic control in sodium chloride solution. Intended as a comparative or quality-control index, the procedure yields a reproducible pitting potential for austenitic, ferritic/austenitic, ferritic and martensitic stainless steels. ISO 15158:2014 is explicit that the measured pitting potential is a relative indicator and is not an absolute predictor of when pitting will occur in real service environments.
Key Topics and Requirements
- Test principle: Ramp the anodic potential of a specimen at a controlled scan rate while immersed in a normalized NaCl solution and record the potential at which stable pitting current is reached.
- Pitting potential definition: The potential where the anodic current density exceeds a threshold (e.g., 10 μA/cm2 or 100 μA/cm2) for a sustained period (60 s) indicating stable pit propagation.
- Electrochemical equipment:
- Potentiostat able to control potential to within ±1 mV.
- High-input-impedance potential-measuring instrument (sensitivity ≈ 1.0 mV).
- Current measurement accurate to about ±2%.
- Cell and electrodes: Use an inert test cell, Luggin capillary with an external reference electrode (commonly saturated Ag/AgCl), and an inert auxiliary electrode (platinum recommended). Control of reference electrode validation is specified.
- Solution and environment: Reagent-grade chemicals and high-purity water recommended; a 1 M NaCl solution is given as a standardized medium. Tests are typically run at (30 ± 1) °C with prior deaeration (N2 or Ar) and controlled stirring or bubbling.
- Specimen preparation: Exposed area minimum 1.0 cm2; recommended final grinding with 600 grit, thorough cleaning (degrease, rinse with high-purity water, ethanol), and a recommended film-stabilization period (minimum 24 h unless otherwise agreed).
- Practical setup details: Solution volume to specimen area ratio (≥ 100 ml/cm2), Luggin tip placement rules, and avoidance of crevice corrosion via specific specimen holders or flushed cells (see annexes).
Applications and Users
ISO 15158:2014 is primarily used for:
- Comparative evaluation of pitting corrosion resistance across lots, heat treatments, surface finishes, and grades of stainless steel.
- Quality control in manufacturing and incoming inspection of stainless-steel products.
- Materials selection studies, specification development, and R&D where rapid electrochemical ranking is needed.
Typical users: corrosion engineers, materials scientists, metallurgists, quality assurance laboratories, and electrochemical testing facilities.
Related Standards
- ISO 17474 - for reference electrode potentials (referenced in ISO 15158).
- JIS G 0577 - referenced pitting potential notation and related practice.
- ISO/TC 156 - technical committee responsible for corrosion standards.
Keywords: ISO 15158:2014, pitting potential, stainless steels, potentiodynamic control, sodium chloride solution, corrosion testing, potentiostat, electrochemical testing, pitting corrosion resistance.
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