Salt Spray Corrosion Principles

The majority of corrosion in metal materials occurs in atmospheric environments, which contain corrosion-inducing factors and components such as oxygen, humidity, temperature variations, and pollutants. Salt spray corrosion is a common and highly destructive form of atmospheric corrosion.

Salt spray corrosion primarily involves the permeation of conductive salt solutions into the interior of metal materials, leading to electrochemical reactions. This results in the formation of microgalvanic cells, with the "low-potential metal-electrolyte solution-high-potential impurity" configuration. Electron transfer occurs, and the metal acting as the anode dissolves, forming new compounds, i.e., corrosion products. Chloride ions play a pivotal role in the corrosion process of salt spray. They possess strong penetration abilities, easily infiltrating the metal's oxide layer and disrupting the metal's passivation state. Furthermore, chloride ions have low hydration energy, making them readily adsorb to the metal surface, displacing oxygen within the protective metal oxide layer, thus causing metal damage.

Salt Spray Corrosion Principles

Salt spray testing is categorized into two main types: natural environmental exposure testing and artificially accelerated simulated salt spray environmental testing. The latter utilizes a testing apparatus, known as a salt spray test chamber, which has a controlled volume and generates a salt spray environment artificially. In this chamber, products are assessed for their resistance to salt spray corrosion. Compared to natural environments, the salt concentration in the salt spray environment can be several times or tens of times higher, significantly accelerating the corrosion rate. Conducting salt spray tests on products allows for much shorter testing durations, with results closely resembling the effects of natural exposure. For example, while it might take one year to assess the corrosion of a product sample in a natural outdoor environment, conducting the same test in an artificially simulated salt spray environment can yield similar results in just 24 hours.

The equivalence between salt spray testing and natural environmental exposure time can be summarized as follows:

24 hours of neutral salt spray testing ≈ 1 year of natural exposure.
24 hours of acetic acid salt spray testing ≈ 3 years of natural exposure.
24 hours of copper salt-accelerated acetic acid salt spray testing ≈ 8 years of natural exposure.

Post time: Oct-26-2023