Overview
ISO 17248:2015 - "Corrosion of metals and alloys - Test method for high temperature corrosion testing of metallic materials by embedding in salt, ash, or other solids" - defines a standardized laboratory method for evaluating high temperature under-deposit corrosion by embedding metallic test pieces in a corrosive powder (salt, ash or other solids) and exposing them to controlled high-temperature atmospheres. The standard specifies two test options: fully embedding (for gravimetric/mass-change measurements) and partially embedding (for examining three interaction zones: embedded, non‑embedded, and the gas/powder interface), and excludes immersion-in-liquid and surface‑deposit methods (covered by ISO 17245 and ISO 17224).
Key topics and technical requirements
- Test options
- Fully embedded: enables mass change (gravimetric) or dimensional measurements; requires multiple specimens for reproducibility (minimum three test pieces).
- Partially embedded: intended for metallographic investigation of the embedded, interface and exposed zones; gravimetric methods are not appropriate.
- Test specimens
- Geometries and minimum sizes are specified (e.g., rectangular plates, discs or cylinders; minimum thickness 1.5 mm; specific minimum surface area or length depending on embedding mode).
- Final surface finish: abrasive polishing to ~15 µm mean particle diameter (examples given from FEPA/JIS/ANSI).
- Machining and cleaning (ultrasonic degreasing in isopropanol/ethanol) and controlled storage (desiccator) recommendations.
- Corrosive powder
- Powder prepared from actual ash/deposits or reagent-grade chemicals; particle size ≤ 100 µm; composition chosen to reflect service environment.
- Safety note: take precautions when handling hazardous ashes, salts or heavy metals.
- Apparatus and environment
- Furnace with a temperature-regulating device, controlled gas supply and flow rate, thermocouples, and an isothermal exposure zone.
- Temperature distribution must be characterized; equipment materials must not react with test atmosphere or powder to a degree that affects results.
- Measurements and examinations
- Gravimetric mass-change protocol for fully embedded tests (descaling procedures referenced).
- Metallographic sectioning and microstructure examination for partially embedded tests.
- Reporting requirements and reproducibility measures.
Applications and users
ISO 17248:2015 is used to assess corrosion resistance where materials contact solid corrosive deposits at high temperature - typical applications include:
- Power-generation and boiler components
- Gas turbines and heat-recovery systems
- Waste‑to‑energy and biomass combustion plants (ash/salt exposures)
- Materials selection, R&D, failure analysis, and quality assurance in metallurgy and coatings industries
Primary users: corrosion engineers, materials scientists, testing laboratories, OEMs, and asset owners concerned with under-deposit high-temperature corrosion.
Related standards (select)
- ISO 17245 - immersion in molten salts (liquid)
- ISO 17224 - surface deposit testing
- ISO 21608 - high-temperature gaseous corrosion testing
- ISO 26146 - metallographic examination after high-temperature exposure
- ISO 8407 - removal of corrosion products (descaling)