ISO 9400:1990

Overview

ISO 9400:1990 - "Nickel‑based alloys - Determination of resistance to intergranular corrosion" specifies laboratory test methods to assess the susceptibility of nickel‑based alloys to intergranular corrosion. The standard defines the term nickel‑based alloy, specifies test apparatus, specimen preparation, procedures and evaluation criteria, and describes four accepted test methods: the iron(III) sulfate – sulfuric acid test, the copper – copper‑sulfate – sulfuric acid test, the hydrochloric acid test and the nitric acid test.

Key topics and requirements

• Four test methods:
  • Method A: Iron(III) sulfate – sulfuric acid boiling test (used with 24 h or 120 h exposure depending on chromium content).
  • Method B: Copper / copper‑sulfate in sulfuric acid (detects chromium‑carbide/nitride related sensitization; evaluation by bending and microscopy).
  • Method C: Hydrochloric acid boiling test (for certain high‑molybdenum alloys).
  • Method D: Nitric acid test (for other specified susceptibilities).
• Apparatus and consumables: Allihn or Soxhlet condenser, 1 dm3 Erlenmeyer flask, glass cradle or specimen supports, boiling chips, silicone grease or PTFE sleeve for joints, heating device, analytical balance and stereoscopic microscope.
• Specimen preparation: Recommended specimen surface area (typically 20–30 cm2), cleaning with chlorine‑free solvents, removal of deformed metal edges after shearing, and surface finishing only as needed to represent service surface.
• Sensitization: Procedures for thermal sensitization (controlled furnace treatment and quenching) are specified; whether to sensitize or test as‑received must be agreed by buyer and seller.
• Evaluation:
  • Mass‑loss corrosion rate (from weighing) or
  • Metallographic examination and bend testing (e.g., 180° bend for Method B) to detect intergranular attack.
• Reporting and agreement: Selection of method, sensitization treatment and acceptance criteria are to be agreed between buyer and seller; direct correlation to in‑service behavior requires matching the service medium.

Applications

• Material qualification and batch acceptance testing of nickel‑based alloys used in chemical processing, petrochemical, power generation and aerospace where intergranular corrosion is a concern.
• Evaluation of heat treatments, stabilizing additions (e.g., Nb, Ti), welding procedures and susceptibility due to carbide or nitride precipitation.
• Comparative laboratory screening of alloys or welds for specification compliance.

Related standards

• ISO 9400 was prepared by ISO/TC 156 (Corrosion of metals and alloys). The document references related material lists and definitions (for example ISO 6372 and ISO 6207) that users may consult when specifying tests or acceptance criteria.

Keywords: ISO 9400:1990, nickel‑based alloys, intergranular corrosion, iron(III) sulfate test, copper‑sulfate test, hydrochloric acid test, nitric acid test, corrosion testing, specimen preparation, sensitization.