ISO 9227

Summary of ISO 9227– Salt Spray Tests

ISO 9227 specifies the apparatus, test solutions, and procedures for conducting three types of salt spray corrosion tests:

• NSS – Neutral Salt Spray
• AASS – Acetic Acid Salt Spray
• CASS – Copper-Accelerated Acetic Acid Salt Spray

These tests are used to assess the corrosion resistance of metallic materials, with or without protective coatings.

Click to view ISO 9227 Test Equipment

1. Scope

The standard covers:

• Requirements for equipment, reagents, and operating conditions.
• Methods for assessing the corrosivity of the test cabinet.

It does not specify:

• Test specimen dimensions,
• Exposure duration,
• Interpretation of results (these depend on individual product specifications).

Salt spray methods are mainly used to detect discontinuities, pores, damages in organic/inorganic coatings and to verify quality consistency.

2. Key Definitions

• Reference material: Material with known test performance.
• Reference specimen: Sample of reference material used to verify repeatability and reproducibility of cabinet performance.
• Test specimen: The actual sample being evaluated.
• Substitute specimen: Inert material (glass/plastic) replacing a test specimen when needed.

3. Principle of Each Test

• NSS: Atomized 5% NaCl solution, pH 6.5–7.2.
• AASS: Same as NSS but acidified with acetic acid, pH 3.1–3.3.
• CASS: AASS solution + copper chloride (0.26 g/L), producing a more aggressive environment.

All tests are performed in a controlled-temperature spray cabinet.

4. Test Solutions

• Prepared with 50 g/L ± 5 g/L NaCl.
• Water conductivity ≤ 20 μS/cm.
• Heavy metal impurities (Cu, Ni, Pb) ≤ 0.005%.
• pH adjusted using suitable acids/bases; pH measured electrometrically.
• Filtered if needed to avoid nozzle blockage.

5. Test Apparatus

• All components in contact with solution must be corrosion-resistant and must not contaminate the spray.
• The spray cabinet ensures uniform distribution of mist; no direct spray hits the specimens.
• Atomizers receive clean, humidified air at 70–170 kPa.
• Collection funnels are used to verify spray rate and uniformity.
• Special cleaning is required before switching from AASS/CASS to NSS.

6. Test Specimens & Arrangement

• Specimens are positioned so that mist falls naturally onto them.
• Different substrate types must not influence each other.
• Orientation and spacing follow the cabinet’s specified zone.

7. Operating Conditions

• Temperature maintained according to test type (typically ~35 °C).
• Spray fallout rate and NaCl concentration must fall within specified limits.
• Tests run continuously for the defined duration.

8. Post-Test Treatment

• Corrosion products removed according to ISO 8407 (for inorganic coatings).
• Organic-coated specimens may require scribing, depending on ISO 17872.

9. Evaluation

Results are evaluated according to relevant ISO coating degradation standards (ISO 4628 series) or specific product standards.
Typical assessments include:

• Degree of blistering,
• Rusting,
• Cracking,
• Flaking,
• Corrosion around scribe marks.

10. Test Report Must Include

• Type of test performed (NSS, AASS, or CASS),
• Test conditions (temperature, pH, spray rate),
• Duration,
• Specimen details: substrate, coating type, thickness, preparation,
• Any deviations from ISO 9227 requirements.