The salt spray test is an environmental test. It uses salt spray equipment to simulate a salt spray environment, checking products or metal materials’ corrosion resistance. Reference standards include GB/T 2423.17, IEC60068-2-11, ISO4628-3, ASTM B117, JIS-Z2371, JIS-G3141, GJB 150.1, MIL-STD-810F, and MIL-STD-883E.
What is Salt Spray Corrosion?
Corrosion means materials get damaged or deterioration due to environmental effects. Most corrosion happens in the atmosphere, which has oxygen, humidity, temperature changes, pollutants, and other corrosive factors. Salt spray corrosion is a common and destructive atmospheric corrosion. Here, salt spray refers to chloride-containing air. Its main corrosive part is ocean sodium chloride, from oceans and inland salty areas.
Salt spray corrodes metal surfaces. Chloride ions break through oxide and protective layers, causing electrochemical reactions with inner metal. Also, chloride ions have hydration energy. They stick to metal pores/cracks, replacing oxygen in oxides. This turns insoluble oxides into soluble chlorides, making passive surfaces active. It harms products badly.
NSS, ASS and CASS
There are 3 tests: neutral salt spray test (NSS), acid salt spray test (ASS) and copper accelerated acetic acid salt spray test (CASS). They differ in standards/methods and are common in artificial three-proof climate tests.
(1) NSS: the earliest and widely used accelerated corrosion test. It uses 5% sodium chloride solution, pH 6–7 as spray liquid. Test at 35℃, with salt spray settlement at 1–2ml/80cm·h.
(2) ASS: developed from NSS. Add glacial acetic acid to 5% sodium chloride solution, making pH about 3. The solution turns acidic, and the salt mist formed at the end also changes from neutral salt mist to acidic. Its corrosion speed is 3 times faster than NSS.
(3) Copper-accelerated CASS: a new fast test. At 50℃, add copper chloride to salt solution, strongly causing corrosion. Its speed is 8 times faster than NSS.
Technical indicators of the salt spray test include salt solution concentration, relative humidity, temperature, salt spray time, storage time, test cycle, fog collection volume, and pH value.
The purpose of the salt spray test is to assess the salt spray corrosion resistance of products or metal materials. Judging the results determines the quality of products. Whether the results are judged correctly and reasonably is crucial for accurately evaluating their corrosion resistance. Judgment methods include: rating judgment, weighing judgment, corrosion product appearance judgment, and corrosion data analysis.
