Environmental Testing - Part 2: Tests - Test Kb: Salt Mist, Cyclic (Sodium Chloride Solution)
|Publication Date:||1 January 1996|
|ICS Code (Environmental testing):||19.040|
This test is intended for application to components or equipment designed to withstand a salt-laden atmosphere, depending on the chosen severity. Salt can degrade the performance of parts manufactured using metallic and/or non-metallic materials.
The mechanism of salt corrosion in metallic materials is electrochemical, whereas the degradation effects experienced on non-metallic materials are caused by complex chemical reactions of the salts with the materials involved. The rate at which corrosive action takes place is dependent, to a large extent, on the supply of oxygenated salt solution to the surface of the test specimen, the temperature of the specimen and the temperature and humidity of the environment.
Apart from the corrosive effects, this test may be used to indicate deterioration of some non-metallic materials by assimilation of salts. In the following test methods, the period of spraying with the relevant salt solution is sufficient to wet the specimen thoroughly. Because this wetting is repeated after intervals of storage under humid conditions (severities (1) and (2) and - in some cases severities (3) to (6)) - supplemented by storage under a standard atmosphere for testing, it goes some way to reproducing the effects of natural environments.
Severities (1) and (2) are intended to be used for testing products which are used in a marine environment, or in close proximity to the sea. Severity (1) should be used to test products which are exposed to the environment for much of their operational life (e.g. ship radar, deck equipment). Severity (2) should be used to test products which may be exposed to the marine environment from time to time but will normally be protected by an enclosure (e.g. navigational equipment which will normally be used on the bridge or in a control room).
Additionally, severities (1) and (2) are commonly used as a general corrosion test in component quality assurance procedures.
Severities (3) to (6) are intended for products where, under normal use, there is a frequent change between salt-laden and dry atmosphere, e.g. automobiles and their parts.
Severities (3) to (6), compared to severities (1) and (2), therefore include an additional storage under a standard atmosphere for testing.
The period of dry atmosphere may happen, in practice, during breaks of operation, e.g. during the weekend. This inclusion of such a dry period in severities (3) to (6) leads to corrosion mechanism which can be quite different from those under constant humid conditions.
The test is accelerated compared with most service conditions. However, it is not possible to establish an overall acceleration factor for ail kinds of specimen (see IEC 355).