What Does Atmospheric Corrosion Test Mean?
The atmospheric corrosion test is a process carried out on a metallic material to determine the rate of its degradation under different environmental conditions. Once the specimen has been exposed to a corrosive environment, several measurements are taken. Tests include weight loss, pit density, depth and other types of measurements.
There are two types of tests: One involves exposing the specimen to the natural environment and taking measurements at different stages, which can extend up to 20 years or more. The other test - called the accelerated test - is done by introducing a corrosive environment in a controlled chamber, and testing the results after several days.
Corrosionpedia Explains Atmospheric Corrosion Test
In the atmospheric corrosive test, there are three common types of specimens:
- The panel
- The stress corrosion cracking specimen
- The tensile specimen
The following factors are used to determine the design and interpretation of these tests:
- The atmospheric condition
- The specimen's shape
- The direction in which the specimen faces
- The amount of shelter, drip, or runoff from other specimens
The panel specimens, which are electrically insulated from the rack, are mounted at 30 degrees from the horizontal and placed facing the source of the corrosive element. Care is also taken to avoid contamination that may drip from the other panels.
Changes in appearance among the panels are checked every year, and some measurements are also taken at predetermined intervals. The tests will normally include the following:
- Reduction in thickness
- Tensile strength changes
- Time to fracture
- Time to perforation
- Time to 10 percent increase in electrical resistance
- Time to initial rust, 10 percent rust, or complete rust
- Changes in ductility
A loss in weight or reduction in thickness per unit of time is the most useful and general measure of corrosion. It is usually given in microns per year (µm/y) or mils per year (mpy)
The results of the tests provide information that can help determine suitable material and coating processes for a particular application and environment. The main sectors that benefit from these tests are the aircraft, automotive, transport, infrastructure and paint industries.