Is the Salt Spray Test Worth It?
Many readers will be familiar with the Salt Spray Test, a test often performed on metallic-coated sheet to test for corrosion resistance in the field. It’s widely used in product and technical literature, data sheets and customer specs by architects and writers.
However, there’s a school of thought out there that says the test is irrelevant, and ultimately, a waste of money for the tester.
Who’s in the right? Below, we dissect the Salt Spray Test in an effort to uncover if it’s worth it for your end use.
Is salt spray testing an accurate way to gauge corrosion in real life?
While it’s impossible to say that an accelerated corrosion test can mirror the exact results in the wild, salt testing does offer a “screening process” of sorts that can eliminate inferior product.
For years, coated sheet (G40, or less) has been passed off as thicker coating weights (G60, G90, etc.), which obviously leads to faster corrosion in the field. While the salt test certainly has limitations – many of which we’ll get into later in this article – it can be used to confirm that the coating thickness you’ve purchased is the coating thickness you’ve received from your seller.
“For example,” GalvInfo states, “if the life to 10% rust is only 40 hours, it is essentially certain that the coating does not meet the thickness requirements of the most commonly used G60 and G90 coatings.”
Further, GalvInfo says the Salt Spray Test can be used to demonstrate the benefit of using a thicker galvanized coating to improve the product life in the field, though they’re quick to point out the limitations of this type of testing.
In short, if you’re using the Salt Spray Test to mimic conditions in the real-world, you may be surprised to find out that your results are not very accurate.
Who can benefit most from the salt spray test?
“In my opinion, the Salt Spray Test is best suited for R&D,” says Jeff Reall, Supplier Quality Manager at Majestic Steel.
While the Salt Spray Test is not beneficial in comparing to a real-world environment, it can be used to compare galvanized, Galvalume and galvanneal in certain environments.
How does the salt spray test work?
The reasons the Salt Spray Test are ineffective at mirroring real-world results lies partially in how it’s conducted.
To conduct the test, samples are placed on wooden racks, and a solution of water and salt chemicals is sprayed onto the samples for a set number of hours. Samples are rotated frequently so all sides are exposed uniformly throughout the test.
Seems simple enough, but why isn’t an effective gauge on real-world wear?
For a number of reasons:
1. Many field applications do not involve exposure to salt chemicals.
2. Even if they are exposed to salt chemicals, it’s rarely at concentrations of 5% – the concentration used during the test.
3. Some surfaces, like galvanized steel, corrode faster in sulphide atmospheres versus sulphide-free atmospheres. This is not something that’s controlled during the salt spray test.
4. Good performance of zinc-based coatings on steel requires drying periods between wetness. The salt spray test does not allow for this drying period.
5. In the test, samples are not exposed to UV light, a common cause of deterioration in paints and primers.
6. Temperatures are set at a constant 95°F in the chamber, which obviously does not mimic real-life conditions.
Overwhelmingly, we can see that there are many factors involved in the deterioration and corrosion of metallic-coated and painted sheet that are not accounted for in the Salt Spray Test, making it useful for some research and development applications, but less so for gauging corrosion resistance in the field.
Can results from UV light, paint fading and chalking can be measured in this test?
No. Unfortunately, the test does not allow for these factors to be incorporated.
Is the Salt Spray Test worth it for your application?
If you’re using it for research comparisons, we’d say you’re on the right track. But if you’re looking to the Salt Spray Test for product failure analysis, you’re probably not producing the results you need.
In those cases, Reall recommends a Magnetic Handheld Test, or a Triple Spot Test (TST) to determine coating weight, and depending on what you’re after, product failure tests like the T-Bend Test, Cup Test or Rockwell (to name just a few) as alternatives to salt spraying.
Not only are these tests traditionally less expensive than salt spraying, but they’re also more accurately able to determine everything from coating weights to paint adhesion to product failure.
For more technical information on the Salt Spray Test, check out this GalvInfo article, The Salt Spray Test.