What is Salt Spray Testing? and How Is It Important?

13 December 2021

A corrosion test is a chemical or electrochemical process in which the effects of corrosive materials on various metals are studied. The salt spray test, also known as "weathering," is an accelerated corrosion testing method for evaluating the durability of finishes and coatings by exposing samples to a mist or aerosol of fine salt particles that mimic natural weather conditions. Let's explore more on the Corrosion test and salt spray test.

What is a Corrosion Test?

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A corrosion test is designed to predict the behavior of a metal in different corrosive conditions by testing it under such conditions. The two main types of corrosion tests are laboratory corrosion tests and field corrosion tests.

Lab tests can be carried out on small metal samples, whereas field tests are used to evaluate large metal objects and structures. Laboratory corrosion tests are carried out in controlled conditions, whereas field tests are carried out in the actual environment where the metal is used.

There are various laboratory corrosion tests, including:
- Closed-loop test
- Electrochemical impedance spectroscopy (EIS)
- Potentiodynamic polarization (PD)
- Salt spray testing (ASTM B 117, EN ISO 9227, ISO 17025 or JIS Z 2371)

What is a Salt Spray Test?

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The salt spray test is a standardized way of accelerating corrosion. It involves a metal sample being placed in a chamber containing a fine mist or aerosol of salt particles, representing natural weather conditions. The damage to the sample is measured visually and compared against other samples, with the results being reported as equivalent "hours at" exposure.

Salt spray testing is used to assess the durability of finishes and coatings on metal surfaces. The test can be used to evaluate the impact of different exposure conditions, such as humidity and temperature, on a coating's ability to resist corrosion. It is also used to compare the performance of different coatings and finishes.

1. NSS or Neutral Salt Spray

Neutral salt spray (NSS) testing is used to evaluate the effect of an environment on a metal's surface without affecting any protective or decorative properties. The corrosion tends to be slow and uniform. It is applicable for ferrous and non-ferrous metals, such as aluminum alloys, magnesium alloys, copper alloys, zinc alloys, and titanium alloys. The test cycle is at a constant chamber temperature of 35 Degrees Celsius.

2. AASS or Acetic Acid Salt Spray

Acetic acid salt spray (AASS) testing is used to evaluate the effect of an environment on a metal's surface with the addition of acetic acid, which enhances corrosive attack. The corrosion tends to be more aggressive and non-uniform. It is primarily used for ferrous metals, such as nickel, steel and iron. The optimum temperature is 50 Degree Celsius.

3. CASS or Copper Accelerated Acetic Acid Salt Spray

Copper accelerated acetic acid salt spray (CASS) testing is used to evaluate the corrosion resistance of zinc, cadmium, and polymer coatings. You can also use it for evaluating the effect of an environment on a metal's surface with the addition of glacial acetic acid and other dihydrate.

The ASTM B117 standard defines the procedures for conducting a salt spray test, approved by the American Society for Testing and Materials. The standard specifies the type of salt to be used, the testing conditions, and the parameters to be measured.

The salt spray test is used to assess the corrosion resistance of coatings and finishes on metal surfaces. The test can be used to evaluate the impact of different exposure conditions, such as humidity and temperature, on a coating's ability to resist corrosion. It is also used to compare the performance of different coatings and finishes.

The standardization of the salt spray test allows results from different laboratories to be compared. This makes it an important tool for assessing the corrosion resistance of new and existing coatings and finishes. Manufacturers are also widely used to demonstrate compliance with environmental regulations, such as the Restriction of Hazardous Substances Directive (RoHS).

What is ISO 17025, and How Does It Relate to the Salt Spray Test?

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ISO 17025 is the international standard for the assessment and calibration of testing laboratories. It specifies the requirements that a laboratory must meet to be accredited. ISO 9227 is also one of the international standards that specifies a calibration method using corrosion reference specimens for evaluating the repeatability and reproducibility of salt spray test. Other important relevant standards to know include JIS Z 2371 and ASTM G85.

Lab accreditation is important because it ensures that the results of corrosion tests, such as the salt spray test, are reliable and reproducible. This makes it possible to use the results of tests conducted by different laboratories for comparing the corrosion resistance of coatings and finishes.

Terminology

Here are some terms that are used in the salt spray test:

  • DI water
    DI water is deionized water. It is used to rinse the metal surfaces before and after the salt spray test.
  • Glacial Acetic Acid
    Glacial acetic acid is an acid that is used in the acetic acid salt spray test. It is a strong and corrosive acid that is used to accelerate the corrosion of metal surfaces.
  • Saline Solution
    Saline solution is a mixture of salt and water used to generate the salt spray in the test. It is also known as sodium chloride solution.

Conclusion

In conclusion, the salt spray test is used to assess the corrosion resistance of coatings and finishes on metal surfaces. The ASTM B117 standard defines the procedures for conducting a salt spray test. ISO 17025 is the international standard for the assessment and calibration of testing laboratories. It specifies the requirements that a laboratory must meet to be accredited. Other important relevant standards are ISO 9227, JIS Z 2371 and ASTM G85.

Lab accreditation is important because it ensures that the results of corrosion tests, such as the salt spray test, are reliable and reproducible. This makes it possible to use the results of tests conducted by different laboratories for comparing the corrosion resistance of coatings and finishes. Salt Spray Testing offered by Thai Parkerizing as part of our Corrosion Testing Services, our standardized testing methods help ensure that your materials will perform as expected in their real-life environment, most of all, that your materials will fit for the purpose of their intended use.

As a leader in coating, surface treatment and heat treatment technology for a wide range of purposes, including customers in the automotive parts industry, we persist in research and development to create effective solutions for customer needs. Our wide range of products and services include surface and metallurgical analysis and various testings presented below.