Interpretation of Salt Spray Test Results

Interpretation of Salt Spray Test Results

Dealing with the corrosive nuts and bolts is the commonest problem that we all have dealt with. Of course, what is claimed on the packings are not real, this is what we assume. But in technical terms, the parameters of manufacturers of measuring the life of nuts and bolts or other metallic components are way different than a layman. They are referring to the test lives their products have survived, which we cannot directly relate with real working conditions. 

When tested in laboratories, the products are subjected to a severe caustic environment that accelerates or at least initiates the corrosion. These conditions are very different from real working conditions. The lab conditions simulated are very aggressive and can result in corrosion in mere few hours. The test specimen is exposed to continuous fog sprays. Whereas in real conditions, the environment is a cycle of the dry and wet environment. 
Does this mean that Salt Spray Tests are less reliable?
Not really. But the way we are interpreting the results is less reliable.
First of all, we need to break the notion that salt spray test determines the corrosion resistance life of the product. We must look out for qualitative analysis that help us in establishing comparative results. For instance, you are the manufacturer of nuts used in the marine application. The sustenance of nuts without plating in the salt spray test is very low. Now, you have coated the samples with different coatings and prepare multiple specimens. All these specimens are subjected to same test for, say, 72 hours. The coating that showed the higher resistance against the fog can be taken further for the manufacturing process.
Another important way of interpreting the salt spray results is a comparative analysis of the production process. Say, 10 years before, your nuts were surviving the test for 48 hours and now they are failing at mere 11 hours. So, you will see that there is no change in the production process, even then there is a regression in the quality, which is why your rejection rate is increasing due to product failure. So, you will understand that your production process needs reconsideration. 
The right way to utilize the salt spray test is to establish a comparative analysis curve, instead of a comparison of salt spray life with real life. 
Corrosion has always been a major issue for engineers and designers of different industries that deal with metal products. Using a standardized test process is very important to deliver high-quality products. 

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