Overview
ISO 16701:2015 defines an accelerated atmospheric corrosion test that combines controlled humidity cycling with intermittent spraying of a salt solution. Developed in the automotive context, the method reproduces cyclic salt and humidity conditions (e.g., winter de-icing salts) to assess the corrosion performance of metals, alloys and coatings under moderately forced laboratory conditions. The standard describes the test method, reagents and procedure, but does not prescribe specimen dimensions, total exposure periods or result interpretation - those are supplied in product specifications.
Key topics and technical requirements
- Test cycle and exposure: The procedure includes a 6 h exposure to a slightly acidified 1 % NaCl solution twice weekly, followed by controlled humidity cycling between 95 % RH and 50 % RH at a constant 35 °C. Test cycles are organized into 12 h sequences with periodic spraying cycles.
- Salt solution: Prepare at 10 g/L ± 1 g/L NaCl in deionized/distilled water (conductivity ≤ 2 mS/m). Adjust pH to 4.2 ± 0.1 with dilute sulfuric acid. Maximum impurity levels for NaCl (e.g., Cu, Ni 0.001 %) are specified.
- Climate chamber: Must control and monitor humidity and temperature closely - instantaneous RH deviation ±4 % (50–95 % RH) and mean RH accuracy ±2 % over 7–8 h. RH must be changeable linearly between 95 % and 50 % within 2 h.
- Spraying device: Produce a uniform vertical mist at a linear flow rate of 15 mm/h ± 5 mm/h (≈ collection 120 ml/h ± 40 ml/h using specified collector). Materials in contact with salt must be corrosion-resistant and not alter corrosivity.
- Forced drying and airflow: A system for forced drying after spray (supercool/reheat or pre-heated airflow) is required to avoid prolonged macroscopic wetness.
- Specimen handling: Non-metallic stands, specimen angle preferably 20° ± 5° to vertical. Protect cut edges and record material, pretreatment, coating thickness and any intentional damage.
- Limitations: Noted risk of exaggerated pitting for some low-alloy/austenitic stainless steels; unsuitable for wax/oil rust protection agents due to constant elevated temperature.
Applications and practical value
- Quality assurance and comparative evaluation of:
- metallic substrates and alloys,
- metallic (anodic/cathodic) coatings,
- chemical conversion coatings, and
- organic coatings on metals.
- Widely used by automotive OEMs and suppliers, corrosion and materials engineers, independent testing laboratories, and coating manufacturers to simulate salt-driven cyclic atmospheric corrosion and benchmark protective systems.
- Corrosion engineers, materials scientists, product and coatings developers, QA/QC labs, OEM specification writers and standards committees seeking a reproducible accelerated test that better correlates with cyclic salt exposure than continuous salt spray.
Related standards
- ISO 4628 series (coating degradation evaluation)
- ISO 8407 (removal of corrosion products)
- ISO 10289 (rating of test specimens after corrosion tests)
- Developed under ISO/TC 156 (Corrosion of metals and alloys)
Keywords: ISO 16701, accelerated corrosion test, humidity cycling, salt spray, 1% NaCl, climate chamber, corrosion testing, coating durability, automotive corrosion testing.