The ISO 9022-4:2015 standard specifies a test method for the tolerance of opticalin struts and their related components in a salt fog environment. This test is designed to evaluate the performance of the instrument under exposure to salt fog conditions, especially corrosion on metal surfaces and blockage of moving parts. By simulating the salt fog environment, the surface protection layer and overall corrosion resistance of the instrument are inspected to ensure that its performance is stable in actual use. The standard is suitable for representative samples or small complete units, and the testing of large instruments or components is performed according to special circumstances. This standard helps manufacturers evaluate and improve the Reliability of instruments in salt fog environments.