SUS316 corrosion resistance test standard
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I. Salt Spray Corrosion Test Standards
ASTM B117 (U.S. Standard)
Test Conditions: 5% NaCl solution spray at 35°C; continuous spray duration can be selected as needed (typically 24–1000 hours).
Evaluation Criteria: Surface rust spots, pit density and distribution are observed; corrosion rate is calculated using the weight loss method (mm/year).
Typical Applications: Simulates marine or industrial salt spray environments, such as ship fittings and outdoor architectural components.
Standard Update: The 2025 edition introduces new requirements for salt spray deposition uniformity inside the chamber (1.0–2.0 mL/80cm²/h).
ISO 9227 (International Standard)
Test Types: Neutral Salt Spray (NSS), Acetic Acid Salt Spray (AASS), Copper-Accelerated Acetic Acid Salt Spray (CASS).
Differences: CASS is more aggressive (contains 0.26g/L CuCl₂), suitable for evaluating coatings or highly corrosion-resistant alloys.
Data Comparison: SUS316 typically withstands 1000 hours in NSS testing without significant corrosion, while 304 stainless steel can only endure around 500 hours.
II. Electrochemical Corrosion Test Standards
ASTM G5 (Potentiodynamic Polarization Curves)
Test Method: Conducted in 3.5% NaCl solution, scan rate of 0.1667 mV/s.
Key Parameters:
Corrosion Potential (Ecorr): SUS316 typically > -200 mV (vs SCE), indicating excellent corrosion resistance.
Corrosion Current Density (Icorr): Typical value < 0.1 μA/cm², better than 304 stainless steel (0.5–1 μA/cm²).
ISO 17475 (Electrochemical Impedance Spectroscopy, EIS)
Frequency Range: 10⁵ Hz to 10⁻² Hz, applying ±10 mV AC signal.
Data Analysis: Equivalent circuit fitting is used to calculate charge transfer resistance (Rct) and double-layer capacitance (Cdl). SUS316 Rct can exceed 10⁵ Ω·cm², much higher than carbon steel (10³ Ω·cm²).
III. Pitting and Crevice Corrosion Testing
ASTM G48 (Chloride Solution Immersion Test)
Test Solution: 6% FeCl₃ solution (pH 1.8–2.0), temperature 50°C.
Evaluation Indicators:
Pitting Potential (Epp): Approximately +500 mV (vs SCE) for SUS316.
Critical Crevice Temperature (CCT): >70°C.
ISO 11846 (Crevice Corrosion in Chloride Environments)
Specimen Design: Crevices formed using PTFE gaskets, crevice width 0.1–0.5 mm.
Typical Results: SUS316 shows no significant crevice corrosion in environments with Cl⁻ concentrations ≤2000 ppm under long-term exposure.
IV. Intergranular Corrosion Testing
ASTM A262 (Corrosion Test After Sensitization Treatment)
Sensitization Procedure: Hold at 650°C for 2 hours, followed by air cooling.
Test Methods:
Practice E (Oxalic Acid Electrolytic Etch Test): Examine grain boundaries under microscope for continuous intergranular attack.
Practice C (Nitric Acid–Hydrofluoric Acid Test): Corrosion rate ratio between sensitized and original samples should be <1.5.
ISO 3651 (Nitric/Sulfuric Acid Testing)
Huey Test: Boil in 70% HNO₃ for 5 cycles (each cycle 48 hours); acceptable if weight loss rate <2.0 g/m²·h.
Strauss Test: Bend specimen 180° after sensitization; pass if no intergranular cracking is observed.
V. Stress Corrosion Cracking (SCC) Testing
ASTM G36 (Boiling MgCl₂ Solution Test)
Test Conditions: 154°C in boiling 45% MgCl₂ solution, under constant load (σ ≥ 0.7σ₀.₂).
Result Evaluation: SUS316 generally does not exhibit SCC under these conditions, while ordinary carbon steel may fracture within hours.
ISO 7539-5 (C-Ring Specimen Method)
Specimen Preparation: Formed into a C-ring and subjected to initial stress (σ = 0.8σ₀.₂).
Typical Data: SUS316 shows SCC incubation time >1000 hours in neutral solutions with Cl⁻ concentration ≤500 ppm.
VI. Food Contact Safety Standards
GB 4806.9-2023 (Chinese Food Safety Standard)
Migration Limits:
Nickel (Ni): ≤0.1 mg/L
Chromium (Cr): ≤0.1 mg/L
Molybdenum (Mo): ≤0.5 mg/L
Test Method: Soak in 4% acetic acid (simulating acidic foods) and 10% ethanol (simulating alcoholic beverages) for 2 hours; migration must meet limits.
EU 10/2011 (EU Regulation for Food Contact Materials)
Special Requirements: For components in long-term food contact, 3 consecutive migration tests must be passed; each test must show ≤0.1 mg/kg migration.
VII. High-Temperature Corrosion Testing
ASTM G150 (Cyclic Oxidation Test)
Test Conditions: 850°C in air, cycle of 1 hour heating + 10 minutes cooling, continued for 500 hours.
Evaluation Criteria: Oxidation weight gain ≤1.0 mg/cm², with no spalling or penetrating oxidation.
ISO 9593 (High-Temperature Sulfidation Corrosion)
Test Gas: Mixture of N₂ containing 1% H₂S, temperature 600°C for 100 hours.
Result Analysis: SUS316 sulfidation corrosion rate <0.1 mm/year, superior to ordinary stainless steel (0.5–1 mm/year).
