Overview
EN ISO 3651-1:1998 specifies the Huey test method for determining resistance to intergranular corrosion of austenitic and ferritic‑austenitic (duplex) stainless steels in a nitric acid medium by measurement of loss in mass. Published by CEN/ISO, the standard defines specimen preparation, corrosive solution, apparatus (reflux or cold‑finger condensers), test procedure and calculation of corrosion rate. It is intended for rolled, forged, tube and cast products destined for oxidizing environments (for example concentrated nitric acid).
Key topics and requirements
- Scope: Applies to austenitic and duplex stainless steels; generally not recommended for molybdenum‑bearing grades unless intended for nitric acid service. Results are specific to the test medium.
- Purpose: (a) verify intrinsic alloy resistance after a sensitization heat treatment; (b) check efficiency of solution treatment on delivered product.
- Sensitization heat treatment: typically 30 min at 700 °C ±10 °C followed by rapid cooling (water); heating ramp not to exceed 10 min. Welded pieces are excluded from sensitization treatment.
- Specimen preparation:
- Mechanical: descaling by grinding with iron‑free abrasive paper, grade 120 or finer; avoid overheating.
- Chemical: limited descaling (≤1 h) in specified HCl/HNO3/water or HCl/water solutions; verify no test‑induced intergranular attack by micro‑examination.
- Degrease immediately before immersion.
- Corrosive solution: aqueous nitric acid, 65 % (m/m) ±0.2 %, analytical grade with low impurities.
- Test procedure: immerse specimen in boiling solution for five periods of 48 h each (fresh solution each period); typical solution volume ≥ 20 ml per cm2 of specimen surface; weigh to 0.001 g and record surface area to ±5%.
- Apparatus: Erlenmeyer flask with cold‑finger or Allihn (reflux) condenser; same condenser type must be used for comparative tests.
- Calculation: report loss in mass and convert to corrosion rate (e.g., mm·a‑1 or g·m‑2·h‑1) using specimen density (e.g., ≈8.0 g·cm‑3 for Cr–Ni–Mo steels, ≈7.9 g·cm‑3 for Cr–Ni steels).
Applications and users
- Who uses it: corrosion engineers, metallurgists, materials laboratories, stainless‑steel manufacturers, fabricators, quality control and procurement specialists.
- When to use: to qualify alloy grades for oxidizing service (nitric acid), verify heat‑treatment/solution treatment effectiveness, assess sensitization susceptibility after thermal cycles (forging, welding, rolling).
- Limitations: test reflects performance in the specific nitric acid medium only; not a universal indicator for pitting, stress corrosion or general corrosion resistance.
Related standards
- ISO 3651-2 - corrosion test in media containing sulfuric acid (complements Part 1)
- Refer to national adoptions (EN ISO 3651-1) and CEN/ISO implementation documents for formal use and reporting requirements.
Keywords: EN ISO 3651-1:1998, Huey test, intergranular corrosion, nitric acid, austenitic stainless steels, duplex stainless steels, loss in mass, corrosion testing.