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In
1998, 1.3 million freight cars and 1,962 passenger cars were operating
in the United States. Covered hoppers (28 percent) and tanker
cars (18 percent) make up the largest proportion of the freight
car fleet. The type of commodities transported range from coal
(largest volume) to chemicals, motor vehicles, farm products,
food products, ores and minerals. Railroad cars suffer from both
external and internal corrosion. The total annual direct cost
of corrosion is estimated to be $0.5 billion, divided over external
coatings ($0.25 billion) and internal coatings and linings ($0.25
billion).
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Railroad freight cars typically suffer from both
external and internal corrosion. While external corrosion, primarily
due to atmospheric exposure, is a concern, car appearance generally
takes precedence. External corrosion is controlled by application
of direct-to-metal coating systems (epoxies with or without urethane
coating). Certain categories of cars, particularly tank cars,
are leased by the shippers; therefore, the lessees often choose
to apply an exterior paint to address the aesthetics. Internal
corrosion is caused by corrosive cargo, such as coal, salt, or
various acids.
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