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Corrosion Test: ISO 9227

Once clarified the importance of performing corrosion tests on components and complete products, we can examine procedures and devices to detect corrosion resistance.

Once clarified the importance of performing corrosion tests on components and complete products, we can examine procedures and devices to detect corrosion resistance.

There are many standards that deal with corrosion testing procedures but we decided to focus on the UNI EN ISO 9227 as this is often re-called in other standards.

Salt spray tests are usually performed to detect discontinuities, pores, defects and damages in organic and inorganic coatings and for quality control purposes.

UNI EN ISO 9227

This test is not a direct indication of the corrosion resistance in all conditions as there are many factors that affect the progress of corrosion: corrosion can vary depending on the environmental conditions and on where the materials tested should be used. This standard gives an indication to check that a metallic material, under corrosion attack, maintain its quality.

The ISO 9227 gives the directions to identify:

  • the main features of the device to conduct tests
  • the chemical solution features and how it should be used
  • 3 main types of test

The device identified is a test chamber for salt-spray test and the Standard define some specific feature of the chamber as, for example the shape of the hood, that should prevent small droplets of water to fall on the specimen, size and dimensions of test cabinet.

3 TYPES OF TESTS

  • the neutral salt spray (NSS)
  • acetic acid salt spray (AASS)
  • copper-accelerated acetic acid salt spray (CASS) tests

NSS - neutral salt spray test applies to metals and their alloys; metallic coatings; conversion coatings; anodic oxide coatings; organic coatings on metallic materials.

AASS - acetic acid salt spray test is performed to test the corrosion resistance of decorative coatings used for copper + nickel + chromium or nickel + chromium or anodic coatings on aluminum.

CASS - copper-accelerated acetic acid salt spray test is performed to test the corrosion resistance of decorative coatings of copper + nickel + chromium, or nickel + chromium or anodic coatings on aluminum.

The UNI EN ISO 9227 gives than, indications about the cabinet temperature, the atomizing pressure, specimen positioning inside the test cabinet, operating conditions and analysis of results.

The duration of the test depends on the existing prescriptions referred to the material of the device under test and when not specified, the timing should be decided by the carrier of the test in accordance with its customer.