Salt fog (aka salt atmosphere or salt spray) testing exposes components to a fine salt fog mist that can result in rusting or corrosion of susceptible materials. Samples to be tested are hung or placed on a rack inside of the salt fog chamber at the orientation that is specified in the applicable test method or otherwise agreed to with the customer. The orientation during testing is important as unintended corrosion can result if the salt fog is allowed to condense and pool on the sample. The samples are then exposed to a salt fog of defined salt content. The salt solution used to provide the salt fog mist is usually a 5 percent by weight NaCl solution with the pH adjusted close to 7.0. The salt fog condensate rate is monitored during the test to verify that the test requirements are met.
The chamber is heated during the test to accelerate the corrosion process. The test is best used to compare the effects of the salt fog test from one sample to another (see Figure 1 below) or to determine whether or not corrosion is observed during the stated test conditions. Even though it is an accelerated test, it is not possible to extrapolate the salt fog test results back to real life conditions or times.
Samples are not typically powered during the salt fog test. However, samples may be powered if care is taken to make sure that any electrical connections are protected from direct exposure to the salt fog to prevent shorting.
Various test methods include specific steps or requirements when performing the test. These can include preconditioning steps, alternating fogging and drying steps and required test specimen orientations. Delserro Engineering Solutions, Inc. (DES) has many years of experience performing salt fog testing and can assist customers in setting up a test using the proper test conditions. Please contact DES for your salt fog testing needs. Examples of common salt fog specifications include:
MIL-STD-883, Method 1009, Salt Atmosphere (Corrosion)
MIL-STD-810, Method 509, Salt Fog
MIL-STD-202, Method 101, Salt Atmosphere (Corrosion)
ASTM B-117, Standard Practice for Operating Salt Spray (Fog) Apparatus