Page 188 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

166 CORROSION CAUSES

TABLE 3.8 Commodities Transported by Railroad Car
Loads
Commodity Group Carloads × 10 3
Coal 7027
Chemicals and allied products 1680
Motor vehicles and equipment 1546
Farm products 1404
Food and kindred products 1282
Nonmetallic minerals 1256
Metals and products 671
Lumber and wood products 645
Waste and scrap materials 581
Pulp, paper, and allied products 547
Petroleum and coke 483
Stone, clay, and glass products 475
Forwarder and shipper-associated traffic 376
Metallic ores 311
Other car loads 7421
Total car loads originated 25,705

While the largest segment of the freight has historically been coal, chemicals and
allied products amount to the second largest group of transported goods, while food
and kindred products make up 5% of transported goods. The latter two groups of
commodities are either corrosive or sensitive to contamination. Nearly 130,000 of the
covered hopper cars are used for transporting plastic pellets, which require liners to
preserve product purity. The liner life is 8–10 years (Coating Industry Expert, Private
Communication, June 2000).
Transportation of coal presents a problem because, when mixed with moisture, it
becomes highly acidic and corrosive to the carbon steel. There are indications that a
large number of cars can be significantly affected by this problem (Coating Industry
Expert, Private Communication, June 2000).
Corrosion is likely to advance further by the use of thawing sheds during the winter
months in cold climates, in which the cars are heated to thaw the coal. According to
some estimates, there are about 100,000 cars used for coal services; therefore, the
problem may be quite extensive (Coating Industry Expert, Private Communication,
June 2000).
Another source of aggressive species is sodium chloride. The cars used to
transport rock salt suffer from advanced corrosion attack and last for approximately
only 3 years (Coating Industry Expert, Private Communication, June 2000). The
high cost of rehabilitation of salt carrying cars created a trend toward using unlined,
covered hopper cars previously utilized to transport grain for rock salt service. When
corrosion becomes considerable, the cars are scrapped. As such a process cannot
continue indefinitely, more and more rock salt is expected to be hauled by trucks
and barges, as the revenue seems to be insufficient to justify the corrosion-related
replacement/rehabilitation costs.