Page 172 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

150 CORROSION CAUSES

systems. Barlo and coworkers (15) conducted a study on the corrosion of electrified
trains that covered a number of transit systems. It was estimated that the damage to
the rail system is primarily caused by a stray current that occurs on the electrified rail
systems.
Transit systems in Chicago, Jersey City, New York City, Washington, DC, San
Francisco, and Los Angeles were subjected to inspection, and it was found that
corrosion-related problems exist, as manifested by the accelerated corrosion of the
insulators of the rail fasteners in Jersey City and New York City, or in the wooden
tie spikes in Chicago. For instance, wooden tie spikes need to be replaced after 6
months instead of the anticipated 25 years. In many instances, there was no formal
tracking of corrosion-related costs.
While ostensibly there is corrosion damage to other related railroad-owned prop-
erty, such as bridges and rail yard structures, from exposure to the elements, the
railroad systems apparently do not consider it to be a major expense, and therefore
do not track the data. No estimate of the cost of corrosion to railroads was possible
from available data.

3.13 GAS DISTRIBUTION

The gas distribution pipeline sector is a part of the oil and gas industry. Figure 3.17
illustrates the different components of a natural gas production, transmission, stor-
age, and distribution system. The components consist of production walls, gathering
lines within the production fields, processing plants, transmission pipelines, compres-
sor stations located periodically along the transmission pipelines, storage wells, and
associated gathering pipelines, metering stations and city gate at distribution centers,
distribution piping, and meters at both residential or industrial sites.
In 1998, the distribution pipeline included 2,785,000 km (1,730,000 miles) of
relatively small-diameter, low-pressure natural gas distribution piping, which is
divided into 1,739,000 km (1,080,000 miles) of distribution main and 1,046,000 km
(650,000 miles) of services. There are nearly 55 million services in the distribution
system. Figure 3.18 shows the distribution pipeline sector with regard to the oil and
gas industry.
Several different materials have been used for main and service distribution piping.
In earlier times, distribution mains were primarily carbon steel pipe. Since the 1970s,
gas distribution plastic mains have replaced carbon steel. Steel mains are installed in
small sections in certain “downtown” locations where the use of plastic is restricted
in some large-diameter applications.
Table 3.2 summarizes the miles of gas distribution main and the number of services
by material.
A large percentage of mains (57%) and services (46%) are metallic systems
(steel/cast iron/copper), and corrosion is a major problem. For distribution pipe,
external corrosion is the primary problem and internal corrosion has also been
observed in some instances. The methods of corrosion monitoring on cathodically
protected piping are similar to the methods used in the case of transmission pipelines