Corrosion Happens: Salt Fog Testing Shows You Where
February 22nd, 2023
What do cars, trucks, boats, airplanes, lampposts, and socket wrenches all have in common? At first glance, it wouldn’t seem to be much. But all are exposed to corrosive effects of weather, water, pollutants, and more. The basic corrosion-resistance evaluation of material and its coating is salt fog testing.
Corrosion costs many millions of dollars annually and left unchecked can cause structural failure. Salt fog testing allows new designs and coatings to be scrutinized in a controlled environment and is useful to determine the corrosion resistance of different metals and finishes.
Elite performs salt fog tests as part of its suite of climatic tests. A product and its exposed surfaces need to go through a gauntlet to meet the necessary qualities to get to market— of these, salt fog is the primary test. Other tests, including dust, chemical fluids, gravel, water, pressure variations, and explosive environments are available for products needing to meet specific requirements.
Kyle Thompson and Chuck Thompson checking a salt fog test at Elite's lab.
Salt fog is a type of accelerated corrosion test that is performed to assess the comparative corrosion resistance of certain materials when exposed to salt fog or salt spray at increased temperature levels. Automotive and aerospace applications make extensive use of salt fog testing to confirm the integrity of materials and coatings. Elite’s long experience in salt fog testing gives its experts the tools to help you navigate what can be a difficult process. Standards for salt fog testing include:
American Society for Testing and Materials (ASTM) B117
- RTCA DO-160
- ASTM G85 seawater
- Acetic acid
Of these, ASTM B117 and MIL-STD-810 are the most common. They call for temperature maintained at 35⁰C in the test chamber as a mixture of 5% sodium chloride in ASTM D1193 Type IV water is introduced at specific air pressures. Exposure is done in 24-hour blocks, with the number of repetitions determined by the type of material and its intended environment.
Effects of long-term salt exposure on exposed surfaces.
Planning a Salt Fog Test
The test plan developed by the customer and the Elite engineer will specify the duration of the testing and the pass/fail criteria used to determine the test’s result.
Elite has two salt fog test chambers:
- Small Cabinet 42”w x 30”d x 36” h, available for SO2 tests in ASTM G85 tests
- Large Cabinet, available for non-SO2 tests, 93"w x 48”d x 48” h
The test plan will specify the sample or samples to be tested, the specific standard to be applied, the duration of the test, and the pass/fail criteria to be used at the completion of the test.
Among the parameters that can be observed in the test sample during the salt fog test:
- The permeability of seals
- The amount of corrosion creepage when a coated surface is scratched, per ASTM D1654
- The level of coating adhesion, per ASTM D3359
- The degree of surface blistering, per ASTM D714
- The degree of material rusting, per ASTM D610
How Does Salt Fog Testing Correlate to the Real World?
Correlation between a real-world environment and salt fog testing in a lab is difficult. Materials and coatings can vary widely. Actual outdoor environments are even more variable at any time of day or in any environment.
The materials industry has chosen the salt fog test as a useful baseline that gives an indication of a corrosion vulnerability. The salt fog test is widely used because of its repeatability.
Corrosion is going to happen in a product’s life. Contact the experts at Elite to find out how to apply the salt fog test to your product.