ISO 21608:2012

Overview

ISO 21608:2012 specifies a laboratory test method for isothermal-exposure oxidation testing of metallic materials under high‑temperature corrosion conditions in gaseous environments. It defines how to run continuous or discontinuous isothermal exposures (single or repeated mass measurements) to determine oxidation kinetics, mass-change behaviour (gross and net), and phenomena such as scale formation and breakaway. Thermal‑cycling oxidation tests are explicitly excluded.

Key topics and technical requirements

• Test types
  • Continuous: single post‑exposure mass measurement for a series of specimens.
  • Discontinuous: repeated mass measurements on a specimen with controlled intermediate cooling.
• Specimens (test pieces)
  • Typical shapes: rectangular plate, disc or cylinder; minimum thickness stated (1.5 mm) and surface finish using abrasives with mean particle diameter ≈15 µm.
  • Final machining and cleaning (ultrasonic degreasing with iso‑propanol or ethanol) required; mass measured with high precision (repeat measurements within 0.05 mg).
• Exposure scheduling
  • Use several exposure times to define oxidation kinetics; duplicate specimens recommended and progressively increasing time intervals (example series shown in the standard).
• Test atmosphere and gas supply
  • Closed systems (preferred) with controlled gas flow, humidifying regulator and hygrometer; deionized water (<1 µS·cm‑1) for humidification when used.
  • Recommended specific humidity for air tests: ~20 g/kg (≈100% RH at 25 °C); gas flow must prevent depletion of reactive species.
• Apparatus and temperature control
  • Isolated furnace/test chamber, gas flow monitoring, and appropriate supports to collect spalled scale.
  • Separate calibrated thermocouples for monitoring (preferred types: K up to 800 °C, S/R up to 1 100 °C, B above 1 100 °C) and temperature tolerances defined by range (e.g., ±2 °C ≤300 °C; ±3 °C 300–600 °C; increasing at higher ranges).
• Measurements and evaluation
  • Procedures for mass‑change determination (gross/net), accounting for adherent vs. spalled scale, post‑test metallographic examination and reporting requirements.

Practical applications - who uses ISO 21608

• Materials and corrosion engineers characterizing oxidation resistance of metals and alloys.
• R&D and quality control labs evaluating high‑temperature materials (power generation, aerospace, petrochemical, furnace components, turbine materials).
• Developers of high‑temperature coatings and protective alloys assessing lifetimes and breakaway behavior.
• Certification and standards laboratories needing a reproducible method to compare oxidation kinetics across materials and environments.

Related standards (normative references)

ISO 21608 cites related test and measurement standards used in implementation, including:

• ISO 3611, ISO 13385‑1 (dimensional measuring equipment)
• ISO 26146 (metallographic examination after high‑temperature exposure)
• ISO 6344‑3 and regional abrasive grain standards (surface finish)
• ASTM guides for thermocouples and metallography (E220, E230, E633, E3, etc.)

ISO 21608 is essential when you need reproducible, standardized isothermal oxidation data for high‑temperature corrosion evaluation of metallic materials. Keywords: ISO 21608, isothermal-exposure oxidation testing, high-temperature corrosion, metallic materials, oxidation kinetics, mass change, thermocouple, gas supply.