© 2006 by Taylor & Francis Group, LLC

110 Corrosion Control Through Organic Coatings
and, being upwind, does not suffer from the refinery. However, they also noted
heavy amounts of dust on the samples at this site, almost certainly from the
cement factory next door. Analysis of the dust showed it to be similar to the
composition of clinker cement. Cement, of course, is extremely alkaline, to
which few polymers are resistant. At the high temperatures at these sites — up
to 49°C — and with the very high amounts of water vapor available, soluble
alkaline species in the dust deposits can form a destructive, highly alkaline
solution that can break down cured binder. The extent to which the various
coatings managed to retain gloss at this site is almost certainly a reflection of
the polymer’s ability to resist saponification.
In a study of coated panels exposed throughout two pulp and paper mills in
Sweden, Rendahl and colleagues [37] found that the amounts of airborne H 2S and
SO 2 at the various locations did not have a significant impact on coating performance.
The effect of airborne chlorine in this study is not clear; the authors note that only
total chlorine was measured, and the amounts of active corrosion-initiating species
at each location are unknown.
Özcan and colleagues [38] examined the effects of very high SO 2 concentrations
on polyester coatings. Using 0.286 atmosphere SO 2 (to simulate conditions in flue
gases) and humidity ranging from 60% to 100% RH, they found that corrosion
occurred only in the presence of water. At 60% RH, no significant corrosion damage
occurred, despite the very high concentration of SO 2 in the atmosphere.
Another study, performed in Spain, indicates that humidity played a more
important role than levels of atmospheric contaminants in predicting corrosion of
painted steel [39]. However, without quantitative data of pollutant levels for Madrid
and Hospitalet, it is impossible to rule out a combination of humidity and airborne
pollutants as the major factor in determining coating performance. In this study,
60 µm chlorinated rubber was applied to clean steel. Painted samples and coupons
of bare steel and zinc were exposed in dry rural, dry urban, humid industrial, and
humid coastal areas. The results after two years are given in Table 6.3.
TABLE 6.3
Performance of Bare Steel and Coated Panels
Location
Type of
atmosphere Humid/Dry
Corrosion of bare
steel
(lm/year)
Degree of
oxidation of
painted
surface (%)
after 2 years
El Pardo Rural Dry 14.7 0
Madrid Urban Dry 27.9 0
Hospitalet Industrial Humid 52.7 0.3
Vigo Coastal Humid 62.6 16
Modified from: Morcillo, M. and S. Feliu, Proc., Corrosio i Medi Ambient, Universitat de
Barcelona, Barcelona, 1986, 312.
© 2006 by Taylor & Francis Group, LLC