EN ISO 17864:2008 PDF

Overview

EN ISO 17864:2008 (ISO 17864:2005) specifies a laboratory method for determining the critical pitting temperature (CPT) of stainless steels under potentiostatic control. The CPT is defined as the lowest temperature on the specimen surface at which stable, propagating pitting occurs under the specified test conditions. This method is rapid - allowing CPT measurement in a single ramped-temperature test - and is intended as a relative index of pitting resistance, not as a prediction of field service behavior.

Key topics and technical requirements

• Scope and materials: Applies to stainless steels (austenitic, ferritic/austenitic (duplex), ferritic).
• Test principle: Heat the test solution to increase specimen surface temperature at a controlled ramp rate while maintaining the specimen potential with a potentiostat; CPT is recorded when current density exceeds a specified value for 60 s (to exclude metastable pits).
• Apparatus:
  • Potentiostat capable of holding potential to within ±1 mV.
  • High-impedance electrode potential measurement and current-measurement accuracy (~±2%).
  • Reference electrode external to the cell connected via a Luggin capillary; typical types (Ag/AgCl, SCE) and their SHE potentials are referenced in the standard.
  • Auxiliary electrode (e.g., platinum) with an area at least equal to the specimen area.
  • Temperature controller and temperature-measurement instrumentation (solution temperature accuracy ±0.4 °C).
  • Test cell and specimen holder constructed from inert materials (glass, PTFE, polycarbonate) and designed to prevent crevice corrosion (Annex B discusses flushed-port/flushed-holder approaches).
• Specimen and cell geometry:
  • Minimum exposed test area: 1 cm².
  • Solution volume / specimen area ratio: at least 100 ml/cm².
  • Luggin tip placement: not closer than ~2× tip diameter from the specimen.
• Calibration: Account for temperature gradients by calibrating specimen surface temperature versus bulk solution (installing a probe