© 2006 by Taylor & Francis Group, LLC

Corrosion Testing — Practice 131
which provides requirements for materials selection, surface preparation, paint application,
inspection, and so on for coatings used on offshore platforms.
8.1.2 CONDENSATION OR HUMIDITY
Many tests are based on constant condensation or humidity. Incidentally, constant
condensation is not the same as humidity testing. Condensation rates are higher in
the former than the latter because, in constant condensation chambers, the back sides
of the panels are at room temperature and the painted side faces water vapor at 40°C.
This slight temperature differential leads to higher water condensation on the panel.
If no such temperature differential exists, the conditions provide humidity testing in
what is known as a ‘‘tropical chamber.” The Cleveland chamber is one example of
condensation testing; a salt spray chamber with the salt fog turned off, the heater
turned on, and water in the bottom (to generate vapor) is a humidity test.
Constant condensation or humidity testing can be useful as a test for barrier
properties of coatings on less-than-ideal substrates — for example, rusted steel. Any
hygroscopic contaminants, such as salts entrapped in the rust, attract water. On new
construction, or in the repainting of old construction, where it is possible to blast
the steel to Sa2 1 / 2, these contaminants are not be found. However, for many applications,
dry abrasive or wet blasting is not possible, and only handheld tools such
as wire brushes can be used. These tools remove loose rust but leave tightly adhering
rust in place. And, because corrosion-causing ions, such as chloride (Cl − ), are always
at the bottom of corrosion pits, the matrix of tightly adhering rust necessarily contains
these hygroscopic contaminants. In such cases, the coating must prevent water from
reaching the intact steel. The speed with which blisters develop under the coating
in condensation conditions can be an indication of the coating’s ability to provide
a water barrier and thus protect the steel.
Various standard test methods using constant condensation or humidity testing
include the International Organization for Standardizaton (ISO) 6270, ISO 11503,
the British BS 3900, the North American ASTM D2247, ASTM D4585, and the
German DIN 50017.
8.1.3 WEATHERING
In UV weathering tests, condensation is alternated with UV exposure to study the
effect of UV light on organic coatings. The temperature, amount of UV radiation,
length (time) of UV radiation, and length (time) of condensation in the chamber are
programmable. Examples of UV weathering tests include QUV-A, QUV-B (® Q-Panel
Co.), and Xenon tests. Recommended practices for UV weathering are described
in the very useful standard ASTM G154 (which replaces the better-known
ASTM G53).
8.1.4 CORROSION TESTS FROM THE AUTOMOTIVE INDUSTRY
The automotive industry places great demands on its anticorrosion coatings system
and has therefore invested a good deal of effort in developing accelerated tests to
help predict the performance of paints in harsh conditions. It should be noted that
© 2006 by Taylor & Francis Group, LLC