Why take a salt spray test ?

In order to verify that the metal parts on the product will not corrode when exposed to the atmosphere or other environments. The product can be placed in the use environment for a long enough time, such as one life cycle of the product. This is time-consuming and laborious, in practice is rarely used.
Thus, a convenient method is needed to evaluate the corrosion resistance of products.
Salt spray test is an accelerated anti-corrosion evaluation method of artificial atmosphere. It atomizes a certain concentration of salt water, and then sprays it in a closed incubator, and observes the change of the tested sample after being placed in the box for a period of time. It reflects the corrosion resistance of the tested sample. It is an accelerated test method, that is, it takes a short time, not a few years, but only a few days or even a few hours.
Although the salt spray test is an effective test method. However, due to many factors affecting corrosion, a single resistance to salt spray cannot be used as a representative of the performance against other media, so the results of the salt spray test cannot be used as the test material in all environments. A direct guide to corrosion performance. Also, the performance of materials in test should not be used as a direct guide to corrosion resistance in service.
Nevertheless, the salt spray test method can still be used as a method for testing the tested materials.


Which products need to be tested by salt spray
metals and their alloys
metal cover
organic overlay
Anodized film

Classification of test methods for salt spray test
Neutral Salt Spray Test (NSS)
Acetic Acid Salt Spray Test (AASS)
Copper Accelerated Acetic Acid Salt Spray Test (CASS)

Commonly used standard type: ISO 9227:2006 Europe (including UK)
ASTM B117-03 USA
DIN 50021:1988 Germany
(1) Neutral Salt Spray Test NSS (Neutral Salt Spray)

Test standard selection
ISO 9227:2006 Europe (including UK)
ASTM B117-03 USA
DIN 50021:1988 Germany
The conditions of several test standards are the same, see the following

Test Conditions
Sodium chloride solution concentration 50g/L ± 5g/L
PH value is 6.5~7.2
The temperature in the test chamber is 35 ± 2°C
(US 35+1.1/-1.7 °C)
The sedimentation velocity of salt spray is 1.5±0.5mL per 80cm² per hour

Sample preparation
The type, quantity, shape and size of the sample shall be determined according to the product standard. If there is no standard, it shall be negotiated by the relevant parties.
Before the test, the sample must be cleaned by an appropriate method, but the protective organic film intentionally coated on the sample should not be washed away.
For cut specimens, the cut area should be protected with paint, paraffin or tape.

Sample placement
The sample is placed in the salt spray box with the tested surface facing upward, and the salt spray is allowed to freely settle on the tested surface, and the tested surface cannot be directly sprayed by the salt spray.
The test surface of the sample should be 20 degrees from the vertical direction.
The samples can be placed on different levels in the box, but they must not be in contact with each other or with the box, and the droplets on the sample must not fall on other samples.
The sample holder is made of glass, plastic and other materials. The material for suspending the sample cannot be metal, but insulating materials such as fiber.

Test time
The test time is determined according to different product specifications. Generally speaking, it is 2/4/6/8/24 hours, and if it is greater than 24 hours, it is an integer multiple of 24 hours.

Post-test sample handling
After the test, take out the sample, dry it naturally in the room for 0.5 to 1 hour, and then gently rinse it with clean running water with a temperature not higher than 40 degrees Celsius to remove the residual salt spray solution, and then blow it dry immediately with a hair dryer.