The oldest and most wildly used cabinet test is ASTM B117 (Test Method of Salt Spray [Fog] Testing), a test that introduces a spray in a closed chamber where some specimens are exposed at specific locations and angles. The concentration of the NaCl solution has ranged from 3.5 to 20%. There is a wide range of chamber designs and sizes including walk-in rooms that are capable of performing this test. Although used extensively for specification purposes, results from salt spray testing seldom correlate well with service performance. Hot, humid air is created by bubbling compressed air through a bubble (humidifying) tower containing hot deionized water.
Salt solution is typically moved from a reservoir through a filter to the nozzle by a gravity-feed system. When the hot, humid air and the salt solution mix at the nozzle, it is atomized into a corrosive fog. This creates a 100% relative humidity condition in the exposure zone. For a low humidity state in the exposure zone of the chamber, air is forced into the exposure zone via a blower motor that directs air over the energized chamber heaters.
"The salt spray fog test, when it's used properly, is one of the most valuable corrosion tests in the world. It has impacted all industries. It has been very valuable in terms of quality control and comparative behavior materials and that's in all walks of life: in the automotive, aircraft and compliance industries, in transportation and infrastructure. Paint coatings are used in all of these industries."
"The test is used widely for paint systems. When it's used properly, for quality control or comparing behavior of materials, it is extremely valuable. For example, cyclic tests that are used now in various industries incorporate the use of B 117. These tests are extremely valuable because they more closely duplicate what happens in service."