How long does one hour of salt spray testing correspond to in natural environments?
Salt spray testing is divided into two main categories: natural environment exposure testing and artificial accelerated salt spray environment testing. The latter involves using specialized equipment, known as a salt spray test chamber, where an artificial salt spray environment is created to evaluate the corrosion resistance of products. Compared to natural environments, the chloride salt concentration in an artificial salt spray environment can be several times or even dozens of times higher than that of a natural environment, significantly accelerating the corrosion process. For example, a product sample that might take one year to corrode in a natural environment can achieve similar results in just 24 hours under artificial salt spray conditions.
Artificial salt spray tests include various types: Neutral Salt Spray Test (NSS), Acetic Acid Salt Spray Test (ASS), Copper-Accelerated Acetic Acid Salt Spray Test (CASS), and cyclic salt spray tests.
1.Neutral Salt Spray Test (NSS Test):
This is the earliest and most widely used accelerated corrosion test method. It uses a 5% sodium chloride solution, with the pH adjusted to a neutral range (6-7). The testing temperature is typically 35°C, and the salt spray fallout rate is between 1-2ml/80cm² per hour.
Time Conversion: 24 hours of NSS testing is equivalent to 1 year in a natural environment.
2.Acetic Acid Salt Spray Test (ASS Test):
Developed from the NSS test, this method adds acetic acid to the 5% sodium chloride solution, lowering the pH to around 3, making the solution acidic. Consequently, the salt spray formed is also acidic, and the corrosion rate is about three times faster than in the NSS test.
Time Conversion: 24 hours of ASS testing is equivalent to 3 years in a natural environment.
3.Copper-Accelerated Acetic Acid Salt Spray Test (CASS Test):
This is a more recent development, primarily used abroad. The test temperature is 50°C, and a small amount of copper salt (copper chloride) is added to the salt solution, strongly inducing corrosion. The corrosion rate in this test is approximately eight times faster than in the NSS test.
Time Conversion: 24 hours of CASS testing is equivalent to 8 years in a natural environment.
Salt spray testing provides a rapid method to simulate long-term corrosion in natural environments. For example, 24 hours of neutral salt spray testing is comparable to 1 year of natural exposure, while more advanced tests like CASS can simulate up to 8 years of corrosion within the same 24-hour period. This accelerated testing helps manufacturers quickly assess product durability and performance in corrosive environments.