Accelerated
Testing/Salt-Spray
Efforts have been made in many
zinc-coated steel applications to develop
the correct test method to determine a proper
"accelerated" lifetime. One test
for corrosion prevention systems in the
United States is ASTM B
117. ASTM Committee G-1 on Corrosion of Metals
has jurisdiction over the salt spray standards
B 117 and G 85. The Committee passed the following
resolution regarding the use of B 117: "ASTM
Committee G-1 on the Corrosion of Metals confirms
that results of salt spray (fog) tests, run
according to ASTM standard designation B 117,
seldom correlate with performance in natural
environments. Therefore, the Committee recommends
that the test not be used or referenced in
other standards for that purpose, unless appropriate
corroborating long-term atmospheric exposures
have been conducted."
"ASTM B 117 and B 368 are best used as
quality control tests assuring that the day-to-day
quality of products and manufacturing processes
are optimized. There are a number of other
corrosion tests which can be used for predicting
performance in service."
Salt spray tests cannot be used to accurately
test zinc-coated steel because they accelerate
the wrong failure mechanism. Without a proper
wet/dry cycle, the zinc coating cannot form
patina layers. The absence of a patina layer
allows constant attack of the zinc metal and
gives a very low prediction of the zinc coating
lifetime.
Limitations of the Salt Spray Test (Zhang)
(588 KB)
