This document specifies the apparatus, reagents, and procedures for the neutral salt spray (NSS), acetate salt spray (AASS), and copper accelerated acetate salt spray (CASS) tests used to evaluate the corrosion resistance of metallic materials. It also describes the method for evaluating the corrosiveness of the test c…
2Expert Interpretation
This article provides an in-depth interpretation of the ISO 9227:2017 international standard for salt spray testing, covering the entire process of equipment requirements, solution preparation, sample processing, and result evaluation for the three test methods: neutral salt spray (NSS), acetic acid salt spray (AASS), and copper-accelerated acetic acid salt spray (CASS), revealing the technical key points of testing the corrosion protection performance of metal materials.
Analysis of the core content of the standard
Test type
Solution pH value
Temperature requirement
Applicable materials
Neutral Salt Spray (NSS)
6.5-7.2
35±2℃
Metal substrate/inorganic coating
Acetic Acid Salt Spray (AASS)
3.1-3.3
35±2℃
Copper + Nickel + Cr decorative plating
Copper Accelerated Acetic Acid Salt Spray (CASS)
3.1-3.3
50±2℃
Aluminum Anodized Layer
Key Technical Requirements of Test Solutions
The standard stipulates that the basis of the three test solutions is 50±5 g/L sodium chloride solution. The key differences are:
NSS solution: It must be prepared with deionized water with a conductivity of ≤20μS/cm and a heavy metal content (Cu+Ni+Pb) ≤0.005%.
AASS solution: Add glacial acetic acid to adjust the pH to 3.1-3.3. Sodium chloride containing anti-caking agents is prohibited.
CASS solution: Additional addition of 0.26±0.02g/L copper chloride (CuCl₂·2H₂O)
Key parameters of test equipment
The standard puts forward strict requirements for the Salt spray test chamber:
Spray uniformity needs to be verified when the volume ≥0.4m³
Collection rate requirement is 1.5±0.5ml/h (80cm² horizontal collection area)
Saturation tower temperature control accuracy is shown in the table below:
Spray pressure (kPa)
NSS/AASS temperature (℃)
CASS temperature (℃)
The organic coating specimens shall be prepared according to ISO 1514 and the scratch treatment shall comply with ISO 17872:
Scratch width 0.2-1.0mm, ≥20mm from the edge
Two scratches perpendicular to each other shall be made on the aluminum substrate
2. Test Chamber Verification
A CR4 grade steel reference specimen (150×70×1mm) must be used for verification:
The mass loss after 48 hours of the NSS test should be 70±20g/m²
The mass loss after 24 hours of the CASS test should be 55±15g/m²
3. Result Evaluation
The standard recommends but does not limit the following evaluation methods:
ISO 4628 series for quantitative evaluation of defects in organic coatings
ISO 8993 grid rating method for pitting corrosion
Mass loss method (must be accurate to 1mg)
Technological Evolution and Standard Changes
Major updates of the 2017 edition:
New definitions of terms such as reference material and reference specimen
Added Chapter 4 "Principles"
Simplified the corrosion chamber verification process in Chapter 7
Allows inspection of equipment operating status during the test
Test Limitations
The standard clearly states: Salt spray test results cannot directly predict the long-term corrosion resistance of materials in actual environments and are only applicable to:
Verification of quality consistency of the same materials
Rapid detection of defects such as coating porosity
ISO 9227:2017 — Corrosion tests in artificial atmospheres - Salt spray tests is an international standard developed by International Organization for Standardization (ISO). This document specifies the apparatus, reagents, and procedures for the neutral salt spray (NSS), acetate salt spray (AASS), and copper accelerated acetate salt spray (CASS) tests used to evaluate the corrosion resistance of metallic materials. It...
What does ISO 9227:2017 cover?
This standard covers: This document specifies the apparatus, reagents, and procedures for the neutral salt spray (NSS), acetate salt spray (AASS), and copper accelerated acetate salt spray (CASS) tests used to evaluate the corrosion resistance of metallic materials. It also describes the method for evaluating the...
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The current published version is ISO 9227:2017, published on 2017-03. Always check for amendments or pending revisions.
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