ISO 3651-1:1998

Overview

ISO 3651-1:1998 specifies the Huey test method for determining the resistance to intergranular corrosion of austenitic and ferritic‑austenitic (duplex) stainless steels in a nitric acid medium. The standard describes sample preparation, optional sensitization heat treatment, the corrosive solution, apparatus (condensers/Erlenmeyer flasks), test procedure (loss‑in‑mass measurements) and reporting requirements. It is intended mainly for steels intended for use in strongly oxidizing media (for example, concentrated nitric acid).

Key Topics and Requirements

• Scope and limitations
  • Applicable to austenitic and duplex stainless steels supplied as rolled/forged products, tubes or castings when intended for oxidizing environments.
  • Not generally recommended for molybdenum‑bearing grades unless destined for nitric acid service.
  • Test result is valid only for the corrosive medium used (nitric acid) and is not a universal indicator for other corrosion types (pitting, stress corrosion).
• Purpose of testing
  • Verification of the alloy’s intrinsic resistance after a sensitization heat treatment.
  • Inspection of the efficiency of solution treatment for thin products (no sensitization).
• Sensitization heat treatment
  • Typical treatment: 30 minutes at 700 °C ± 10 °C followed by rapid cooling (water). Heating ramp limited to 10 minutes; welded pieces are excluded from sensitization.
• Specimen preparation
  • Mechanical: descaling by grinding with iron‑free abrasive paper (≈120 grit or finer).
  • Chemical: limited descaling in specified HCl/HNO3/water solutions (ensuring no test artifact).
  • Degrease, rinse and dry immediately before testing.
• Test procedure
  • Corrosive solution: aqueous nitric acid ~65% (analytical quality).
  • Use at least 20 ml of solution per cm² of specimen surface.
  • Immerse and boil specimen for five periods of 48 h each, using fresh solution each period; weigh after each period to determine mass loss.
  • Typical apparatus: Erlenmeyer flask with cold‑finger or Allihn condenser; avoid acid fume escape and excessive bubbling.
• Results and calculation
  • Corrosion expressed as mass loss and converted to corrosion rate (e.g., mm/year or g·m⁻²·h⁻¹) from measured mass loss, surface area, density and time.
• Reporting
  • Include reference to ISO 3651-1, steel grade, heat treatment, condenser type, mean corrosion rate and any incidents.

Applications and Who Uses It

• Metallurgists and materials engineers for alloy qualification and R&D
• Quality control and production teams at stainless steel manufacturers
• Welding and fabrication inspectors assessing post‑weld sensitization risk
• Specifiers and procurement professionals requiring evidence of performance for nitric acid service
• Corrosion consultants and testing laboratories performing intergranular corrosion evaluation

Related Standards

• ISO 3651-2: corrosion test in media containing sulfuric acid (Part 2) - referenced directly in the ISO 3651 series.

Keywords: ISO 3651-1, Huey test, intergranular corrosion, stainless steels, austenitic, duplex, nitric acid, loss in mass, sensitization, corrosion test.