© 2006 by Taylor & Francis Group, LLC

150 Corrosion Control Through Organic Coatings
performance, or even relative ranking, of coatings in most applications, it is the most
frequently specified test for evaluating paints and substrates.
8.4.1 THE REPUTATION OF THE SALT SPRAY TEST
The salt spray test has such a poor reputation among workers in the field that the
word ‘‘infamous” is sometimes used as a prefix to the test number. In fact, nearly
every peer-reviewed paper published these days on the subject of accelerated testing
starts with a condemnation of the salt spray test [39-44]. For example:
• ‘‘In fact, it has been recognized for many years that when ranking the
performance levels of organic coating systems, there is little if any correlation
between results from standard salt spray tests and practical experience.”
[3]
• ‘‘The well-known ASTM B117 salt spray test provides a comparison of
cold-rolled and electrogalvanized steel within several hundred hours.
Unfortunately, the salt spray test is unable to predict the well-known
superior corrosion resistance of galvanized relative to uncoated cold rolled
steel sheet.” [45]
• ‘‘Salt spray provides rapid degradation but has shown poor correlation
with outdoor exposures; it often produces degradation by mechanisms
different from those seen outdoors and has relatively poor precision.” [46]
Many studies comparing salt spray results and actual field exposure have been
performed. Coating types, substrates, locations, and length of time have been varied.
No correlations have been found to exist between the salt spray and the following
service environments:
• Galveston Island, Texas (16 months), 800 meters from the sea [47]
• Sea Isle City, New Jersey (28 months), a marine exposure site [48]
• Daytona Beach, Florida (3 years) [49]
• Pulp mills at Lessebo and Skutskar, Sweden, painted hot-rolled steel
substrates (4 years) [50] and painted aluminium, galvanized steel and
carbon steel substrates (5 years) [51]
• Kure Beach, North Carolina, a marine exposure site [52-54]
8.4.2 SPECIFIC PROBLEMS WITH THE SALT SPRAY TEST
Appleman and Campbell [55] have examined each of the accelerating stresses in
the salt spray test and its effect on the corrosion mechanism compared to outdoor
or ‘‘real-life’’ exposure. They found the following flaws in the salt spray test:
a. Constant humid surface
• Neither the paint nor the substrate experience wet /dry cycles. Corrosion
mechanisms may not match those seen in the field; for example,
in zinc-rich coatings or galvanized substrates, the zinc is not likely to
form a passive film as it does in the field.
© 2006 by Taylor & Francis Group, LLC