Salt spray testing - Reality 2

[freewilly]

Hi All

I have recently had a some componets salt spray tested, but I have not been able to find any info to translate the test results into how the parts will perform in the real world. Can any one point me in the right direction of any info.

Thanks in advance

 

[israelkk]

Salt spray test is a common test for all metal coatings, platings, and surface finishing in military, marine and aerospace engineering. For example for zinc coating the ask for 96 hours in 5% solt spray for Sulphoric anodize of aluminum alloys it is over 300 hours. From my experience this fairly represents real life situations. However, I haven't seen a table the correlate real life environment to salt spray tests.

 

[swall]

There is no correlation between salt spray testing and real world corrosion.Salt spray tests are mainly used as a QC check on parts that have been coated.

 

[RRahul]

It depends on what appliation your component is used.

 

[Compositepro]

Salt spray testing is useful for comparing corrosion resistance of different specimens but does not really correlate to real world conditions. In fact, corrosion is usually worse than if real seawater is used.

 

[kenvlach]

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

http://www.finishing.com

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…”

http://www.finishing.com/3000-3199/3010.html

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”

http://www.finishing.com/4400-4599/4577.html

4844. Salt Spray performance on galvanized steel “We have seen results where the galvanized coating has been eroded during the salt spray test…”

http://www.finishing.com/4800-4999/4844.html

6553. “nobody can directly correlate salt spray hours to real service life”

http://www.finishing.com/65/53.html

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.”

http://www.finishing.com/68/23.html

7459. “Salt spray does not correlate to real life.”

http://www.finishing.com/74/59.html

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.”

http://www.finishing.com/88/85.html

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.”

http://www.finishing.com/89/04.html

11098. Standards for certain laboratory testings “…2.copper accelerated salt spray test(cass) 3.acetic accelerated salt spray test…”

http://www.finishing.com/110/98.html

 

[kenvlach]

(continued from above)
11430. “Salt spray testing is merely a "screening" test to help indicate inferior finishes…If you refer back to ASTM B117, there are several paragraphs which indicate that there is no direct correlation between salt spray and real world performance.”

http://www.finishing.com/114/30.html

13909. Salt spray correlation [Connecticut] “A well anodized surface will last longer in a salt spray cabinet, and in the real world, than a poorly anodized surface. End of correlation”

http://www.finishing.com/139/09.html

14488. Salt Spray Standards - What do they really indicate? [Arizona] “Salt spray hours are simply a general measure of quality”

http://www.finishing.com/144/88.html

17163. Corrosion resistance of zinc-dichromate in marine environment [Illinois] “There is no real correlation between salt spray hours and hours in shipment on the seas.”
“The best use of salt spray is as a process control tool.”

http://www.finishing.com/171/63.html

17951. Relevance of Salt Spray Test [India] “Automotive companies are increasingly moving towards using cyclic corrosion test methods such as GM9540P and SAE J2334. These tests use different test solutions and chamber conditions in an attempt to correlate lab results to proving ground results and real-life service.”

http://www.finishing.com/179/51.html

Lots more, but you can get the point from these.
Ken

 

[unclesyd]

I think the only salt spray test that mattered was the one at Kure Beach, North Carolina, USA operated by International Nickel Company and others.

We had two salt spray cabinets set up for about 10 years to evaluate coatings/paints for on site use for all our facilities. Using panels supplied by the manufacturer vs outdoor exposure of KTA panels we got a very little correlation between the two testing procedures. We did get pretty good correlation on panels tested at Kure Beach and our site’s outdoor panels, near a saltwater bay.

With the cabinets we did detect some changes in formulations of coatings/paints that were not mentioned until we asked why the change in results. Some were very dramatic like a Coal Tar Epoxy going from >1000 Hrs to 300-400 Hrs. We could also determine the criticality of the mixing and application procedures.

One of the cabinets is now a fish smoker at my house.