What Is a Salt Fog or Salt Spray Testing Service?
A salt fog or salt spray testing service evaluates the corrosion resistance of metal materials or parts with plated or painted coatings by subjecting them to accelerated corrosion in a salt-rich atmosphere.
Functions that should be maintained over a long period of time, even years, in a natural environment are evaluated on a time basis. In coastal areas, sea salt particles are blown in by sea breezes, and in snowy areas, calcium chloride sprinkled on roads to prevent them from freezing can easily cause rusting. A salt fog or salt spray testing service is conducted to confirm the corrosion resistance of products under such conditions so that they will not be rendered unusable due to rust.
The salt fog or salt spray testing service is regulated by the ISO (International Organization for Standardization). Standards of overseas countries, and standards of automobile manufacturers, specify the test method, testing equipment, and criteria for judgment. A salt fog or salt spray testing service is also sometimes called SST (salt spray test).
Uses of Salt Fog or Salt Spray Testing Services
Salt fog or salt spray testing services are used to evaluate the durability of metal materials against corrosion in a natural environment. The purpose is to verify the quality of metal products that are used outdoors for long periods of time with respect to the occurrence of rust.
Specifically, the test is used to evaluate the corrosion resistance of plating and coating applied to automobiles, construction materials, and their parts. In the case of automotive parts, especially screws used in parts that are loosened or tightened for maintenance and oil pans made of steel plates, high corrosion resistance is required. Salt fog or salt spray testing services are used to evaluate the durability of not only products but also plating and paint against corrosion.
Principle of Salt Fog or Salt Spray Testing Services
Salt fog or salt spray testing services are performed using a special salt fog or salt spray testing machine. The salt fog or salt spray testing services continuously spray a salt-containing solution in a predetermined amount while maintaining a constant temperature to keep the inside of the test chamber in an environment conducive to corrosion.
Test specimens and parts to be tested are left in the test chamber, and the progress of corrosion is observed. After a predetermined time from the start of the test, the test object is removed and the corrosion resistance of the test object is confirmed by measuring the mass loss due to corrosion and visually confirming physical destruction.
Salt fog or salt spray testing services are conducted in accordance with industrial standards such as ISO. The typical test standard is as follows:
- ISO 9227:2017: corrosion tests in artificial atmospheres – salt spray tests
Other Information on Salt Fog or Salt Spray Testing Services
1. Equivalent Time for Salt Fog or Salt Spray Testing Services
Salt fog or salt spray testing services are used to verify the quality of plating, coating, and industrial products to prevent rust formation in the daily environment where they are used as products. It is one of the accelerated tests to evaluate corrosion resistance in terms of time, which is required in terms of years. However, various industrial standards do not specify the correlation between the natural environment and the test environment.
Each product manufacturer has its own standard for the correlation of how much elapsed time in salt fog or salt spray testing services corresponds to that in the natural environment. Test methods and conditions are in accordance with various industrial standards, and the evaluation time under the specified conditions is determined by each company or industry.
2. Tests Other Than Salt Fog or Salt Spray Testing Services
Salt fog or salt spray testing services can reproduce the “salt environment” and “temperature and humidity changes in a salt-water environment” when the product is used. This is useful for confirming corrosion that may occur in actual use and for reproducing the failure of parts.
There are also several tests that are similar to salt fog or salt spray testing services. For example, the salt-water combined cycle test is a combination of the salt fog or salt spray testing services and the cath test, in which a solution of copper chloride added to salt water is sprayed instead of salt water. Depending on the event to be confirmed and the material to be tested, several combinations of testing methods are available.