Overview
EN ISO 9400:1995 / ISO 9400:1990 specifies laboratory methods for determining the resistance of nickel‑based alloys to intergranular corrosion. It defines the term “nickel‑based alloy,” lists required apparatus and specimen preparation, describes four wet‑chemical test methods (A–D), and gives procedures for evaluation. The standard is intended to assess susceptibility under controlled conditions; correlation to field service depends on matching test medium and thermal history.
Key topics and technical requirements
- Scope and definition
- Applies to nickel‑based alloys; relevant to alloys listed in ISO 6207.
- Methods are for laboratory susceptibility testing - acceptance criteria and choice of method must be agreed between buyer and seller.
- Four prescribed methods
- Method A (iron(III) sulfate – sulfuric acid test): detailed solution preparation (example: prepare 600 cm3 by mixing 400 cm3 water, ~236 cm3 95–98% H2SO4 and 25 g Fe(III) sulfate nonahydrate), boiling exposure, and exposure times (typically 24 h for <18% Cr, 120 h for >18% Cr). Notes on iron consumption and need to add inhibitor during high corrosion.
- Method B (copper – copper‑sulfate – 16% H2SO4 test): solution example (100 g CuSO4·5H2O in 700 cm3 water + 100 cm3 H2SO4 diluted to 1 000 cm3; ≈6% CuSO4, 16% H2SO4), boiling for 24 h (longer possible). Evaluation via bend/flatten and stereoscopic microscopy or metallography.
- Method C (hydrochloric acid test) and Method D (nitric acid test) are specified for other types of intergranular attack (details given in standard).
- Apparatus and specimen preparation
- Typical apparatus: Allihn/Soxhlet or condenser, 1 dm3 Erlenmeyer flask, glass cradle, boiling chips, heating device, silicone grease/PTFE sleeve, analytical balance and stereoscopic microscope.
- Specimen area recommended: 20–30 cm2. Surface finish should represent service surface; carburized surfaces require special care. Sensitization (thermal treatment and quench) procedures are specified when needed.
- Evaluation methods
- Mass‑loss corrosion rate calculation (formula and constants provided) and metallographic examination.
- Method B includes mechanical bend/flatten testing with microscopy to detect intergranular cracking.
Applications and users
- Used by corrosion laboratories, materials engineers, alloy manufacturers, fabricators and quality assurance teams to:
- Screen nickel‑based alloys for susceptibility to intergranular corrosion.
- Evaluate effects of heat treatment, stabilizing elements (Nb, Ti), and welding procedures.
- Support procurement/specification decisions and acceptance testing for components in chemical, petrochemical, and power industries.
- Particularly useful where service environments or fabrication steps may promote chromium carbide or nitride precipitation.
Related standards
- ISO 6207 (alloys listing referenced)
- ISO 6372‑1 (definition consistency)
- Prepared by ISO/TC 156 (Corrosion of metals and alloys)
Keywords: EN ISO 9400:1995, ISO 9400:1990, nickel‑based alloys, intergranular corrosion, iron(III) sulfate test, copper‑sulfate test, corrosion testing, specimen preparation, metallographic examination.