Laboratory salt spray corrosion tests

A laboratory salt spray test, also known as a salt spray corrosion test, is a standardized method used to assess the corrosion resistance of a coated or treated sample. It involves exposing the sample to a controlled environment of saltwater mist to simulate the corrosive effects of salt water.

During a laboratory salt spray test, the sample is placed in a controlled test chamber where it is exposed to a fine saltwater mist. The chamber creates a corrosive environment that simulates the effects of exposure to salt water. The sample is observed over a set period to assess its corrosion resistance and any degradation that occurs.

There are different types of salt spray tests carried out in laboratories, including at Filab, such as:

• Neutral Salt Spray (NSS): This test uses a sodium chloride solution to create a neutral salt spray environment.

• Acetic Acid Salt Spray (AASS): this test adds acetic acid to the sodium chloride solution, creating an acidic salt spray environment.

• Cyclic Corrosion Test (CCT): this test alternates between salt spray and other environmental conditions, such as humidity or drying, to simulate real corrosion cycles.

Materials that can be tested by a salt spray testing laboratory mainly include metallic materials such as steel, aluminum, copper, and their alloys.

However, it is also possible to test other materials such as stone, ceramic, and polymers. These materials are generally coated with a surface coating intended to provide a certain level of protection against corrosion of the underlying metal.

If you are part of the following industries, you may need Filab and its salt spray testing laboratory for your operations. The tests carried out ensure the quality, durability, and reliability of your products in corrosive environments.

• The automotive industry: Salt spray tests are used to assess the corrosion resistance of automotive components exposed to corrosive environments, such as salted winter roads or coastal areas.

• The aerospace industry: Salt spray tests make it possible to verify the corrosion resistance of materials and coatings used in aircraft, which are subjected to extreme environmental conditions.

• The maritime industry: Salt spray tests are important for assessing the corrosion resistance of ships, marine structures, and equipment used in marine environments, where they are exposed to salt water.

• The outdoor equipment industry: Products such as garden furniture, barbecue grills, sports equipment, and leisure equipment must be resistant to corrosion caused by outdoor conditions, including exposure to saline elements.

• The coatings and paints industry: Coatings and paint manufacturers carry out salt spray tests to assess the effectiveness of their products in terms of corrosion protection.

• The electronics industry: Electronic devices used in saline environments, such as marine equipment, must be tested in salt spray to ensure they are capable of withstanding corrosion.

• The construction materials industry: Materials used in construction, such as metal coatings and steel structures, must be tested in salt spray to guarantee their durability and corrosion resistance in corrosive environments.

Neutral salt spray (NSS) and acetic acid salt spray (AASS) tests are industrial testing techniques used to assess the corrosion resistance of different materials. The choice between these two tests depends on the environment in which the material will be used.

The NSS test applies a neutral saline solution to the material, while the AASS test uses an acetic solution to simulate exposure to industrial gases and fumes. Although these tests are similar, they have important differences in how they are carried out and interpreted.

The salt spray (BS) technique is an accelerated corrosion method that evaluates a material's or coating's resistance to atmospheric corrosion. It subjects the sample to a constant humid and saline atmosphere, simulating severe corrosive conditions. However, BS is a qualitative or semi-quantitative test that does not provide detailed information on corrosion mechanisms.

Electrochemical measurements carried out with a potentiostat, such as potentiodynamic polarization curves (Tafel) or electrochemical impedance spectroscopy (EIS), make it possible to precisely quantify corrosion kinetics and study the electrochemical processes at the material/environment interface.

The correlation between these two approaches lies in their complementarity. BS makes it possible to quickly identify the most resistant materials or coatings, while the potentiostat provides the fundamental data needed to understand why they are resistant or how they degrade. For example, after a salt spray test, the potentiostat can be used to:

• Assess coating degradation: Measure the coating's impedance after exposure to BS to quantify its loss of integrity and barrier properties.

• Determine the corrosion rate of the substrate: If the coating is damaged, electrochemical measurements on the exposed substrate can provide the residual corrosion rate.

• Understand protection mechanisms: Analyze the electrochemical data to identify whether protection is due to a barrier effect, passivation, or other electrochemical mechanisms.

This combination offers a more comprehensive approach to evaluating and understanding the corrosion resistance of materials.