freewilly,
Salt spray testing is useful as in QC to detect poor coatings, and it allow some qualitative comparisons (at least, between coatings of the same material – not so good between different coating types).
Compositepro is also correct that at equivalent concentrations, salt spray testing with pure NaCl in DI water (e.g., ASTM B117) is more corrosive than seawater. U. R. Evans, in
The Corrosion and Oxidation of Metals, pp. 164-5 (1960), mentions that this is due to the inhibitive effect of Ca and Mg, which can form protective carbonate and hydroxide films. Likewise, as road de-icers, calcium chloride is less harmful than sodium chloride to auto bodies thread338-68166.
Trying to obtain ‘real world’ corrosion correlations from salt spray test results has been a frequent subject at the
forum. Responses to these Letters may interest you:
Letter#’s
3010. Corrosion testing “You cannot do that through salt spray, because this is only one point on a curve…”
4577. Salt spray and statistics “ASTM B-117 (the test method for Salt Spray) has been reduced in rank (from a test method to a guide) because of the variation”
4844. Salt Spray performance on galvanized steel “We have seen results where the galvanized coating has been eroded during the salt spray test…”
6553. “nobody can directly correlate salt spray hours to real service life”
6823. Salt spray test “The salt spray test (ASTM B117) is a process control tool. It does not, in itself, have a correlation to a product's service life. There are other tests which incorporate a salt spray cycle along with humidity, drying, etc. which have been found to provide correlation to field exposure. One of these tests is SAE J2334.”
7459. “Salt spray does not correlate to real life.”
8885. Reducing time for salt spray testing “There are corrosion tests that have been developed in efforts to improve upon salt spray. You will want to also review specifications for the Kesternich test that uses sulfur dioxide, CASS test (ASTM B368) that uses copper ions and acetic acid, cyclic tests such as GM9540P and SAE J2334. These are all different accelerated corrosion tests.”
8904. Salt Spray Hours “The answer is that salt spray does not correlate to anything. Which one of the eight types of corrosion are you trying to duplicate?… A 100 hours in the salt spray cabinet was equivalent to a month exposure in the Panama Canal Zone…approximately 100 hours salt spray is similar to one year outdoors based on OEM testing in the US….100 hours in the salt spray could also be 15 years in the desert.”
11098. Standards for certain laboratory testings “…2.copper accelerated salt spray test(cass) 3.acetic accelerated salt spray test…”
