An inappropriate example of choosing a salt spray test to evaluate the corrosion resistance of fasteners

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An inappropriate example of using a salt spray test to evaluate the corrosion resistance of fasteners: In aircraft, the surfaces of fasteners are plated with cadmium and then treated with chromates. The standard requires exposure to 5% NaCl salt spray for 96 hours. However, fasteners that passed the tests developed severe rusting within just 1 to 1.5 years of being used in aircraft. The reason is that the media with which the fasteners come into contact during use include SO2 emitted from exhaust pipes, cleaning solutions used during aircraft cleaning, and strippers used before repainting, etc., which are quite different from the salt spray used in the tests. Analysis: The salt spray test is a type of laboratory accelerated test. By intensifying the test conditions, accelerated testing can yield results in a relatively short period of time. Obviously, the environmental conditions of accelerated testing can differ significantly from those in which the material will be used. Therefore, there is no inevitable connection between the results of accelerated testing and the corrosion resistance of the material in actual use. Currently, accelerated testing, as a quality control method for coatings, is primarily used to assess atmospheric corrosion. Therefore, the result of a salt spray test on coated layers can by no means indicate that they will also exhibit good corrosion resistance in other operating environments. It is evident that salt spray testing is an inappropriate choice for evaluating the corrosion resistance of these fasteners.