Salt spray testing in the laboratory

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.

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, ceramics, and polymers. These materials are generally coated with a surface coating designed to provide a certain level of protection against corrosion of the underlying metal.

The salt spray (SS) test is an accelerated corrosion method used to assess a material or coating’s resistance to atmospheric corrosion. It exposes the sample to a constant humid and saline atmosphere, simulating severe corrosive conditions. However, SS is a qualitative or semi-quantitative test that does not provide detailed information about corrosion mechanisms.

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

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

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

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

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

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

Yes, a salt spray test can be considered for an assembly, subject to its compatibility with the chamber and test protocol. It makes it possible to observe the behavior of contact areas, fasteners, and interfaces. Additional investigations may be required to determine whether the damage is related to galvanic coupling between the metals.

Exposed parts may suffer visible damage or deterioration that is not immediately perceptible. Their reuse in production or service should therefore not be assumed, even if their appearance seems satisfactory. It is preferable to provide samples dedicated to the test and to agree on their subsequent use with the laboratory in advance.

A non-conforming result should prompt an investigation into the cause of the deviation before modifying the material or treatment. Depending on the defects observed, FILAB may recommend additional analysis of the coating, surface, or composition, as well as electrochemical investigations. These examinations help guide corrective actions; a subsequent test can then verify their effectiveness in accordance with the agreed protocol.

To obtain a quote from FILAB, specify the material, coating, dimensions, and number of parts to be tested, as well as your deadline. Attach your specifications if available. Not sure which protocol to choose? Explain your requirements to the laboratory so it can define the appropriate tests.