Salt fog and salt spray tests are both used to simulate the effects of saltwater exposure on materials and coatings. However, there are some key differences between the two tests.

A salt fog test, also known as a salt mist test, involves exposing a sample to a fine mist of saltwater in a controlled chamber. The exposure time can range from a few hours to several weeks, and the test conditions can be adjusted to simulate different types of saltwater environments. The sample is typically observed periodically to evaluate the extent of corrosion or degradation.

A salt spray test, also known as an ASTM B117 test, involves exposing a sample to a continuous mist of saltwater in a controlled chamber. The exposure time is typically much shorter than in a salt fog test, usually ranging from 24 to 48 hours. The test conditions are standardized, with a specific concentration of salt, a specific spray rate, and a specific temperature range.

The main difference between the two tests is the way in which the saltwater is applied to the sample. In a salt fog test, the saltwater is delivered as a fine mist, whereas in a salt spray test, the saltwater is delivered continuously as a spray. This difference in application can affect the way in which the sample corrodes or degrades, making one test more appropriate than the other depending on the specific application or material being tested.

Ultimately, the choice between a salt fog and a salt spray test will depend on the specific requirements of the testing standard and the material being evaluated. It is important to consult the relevant standards and procedures to ensure that the most appropriate test method is used.