IEEE Electrification Magazine - September 2014 - 23

while reduction (gain of electrons or decrease in the
oxidation state) takes place at the cathode, which
causes the anode to dissolve while the cathode
remains intact. An electrolyte is defined as a solution
of acids, bases, or salts containing free ions through
which the electric current flows. In the case of electrolysis of underground structures, the moisture in
the soil along with its dissolved acids, salts, and alkalis
acts as the electrolyte, whereas the metal utility pipes
act as electrodes [3].
The following equations represent a typical
anode and cathode reaction, where oxidation
occurs when current leaves the rail and goes into
the earth (anode reaction), whereas the reduction
occurs when the current returns to the rail (cathode reaction):
M " M ++ + 2e (oxidation at anode)
O 2 + 2H 2 O + 4e " 4OH (reduction at cathode).

clips, and well-graded ballast at increased distances, were
seen to provide a relatively higher level of stray-current
protection. Some examples of different track types are
shown in Figure 1.

Corrosion
Corrosion is normally defined as the deterioration of a
material, commonly referred to as rusting, because of its
interaction with the environment: air, water, or soil [2]. In
simple terms, the corrosion process is a natural chemical
reaction between a metal and its surroundings in which
the metal is oxidized (loses electrons), resulting in changes
to the properties of the metal. The corrosion tendency varies for different metals and is highly dependent on the
surrounding environment.
The process of corrosion requires four elements: an electrolyte, an anode, a cathode, and a conductive path. Oxidization (loss of electrons) takes place at the anode, forming ions,

Although generally referred to as electrolysis,
stray-current corrosion is the process where chemical changes take place in the electrolyte when dc
flows through a metal [4]. The rail-based corrosion
is expedited due to electrolysis caused by dc at the
contact point, with wet debris (mud and slime)
building up under the rail base and due to deicing
salts and agricultural fertilizers. Although the physics for stray-current corrosion is the same as for
galvanic corrosion, the underground metal loss is
much faster because of the large amount of straycurrent leakage [5]. Because of the variability in the straycurrent and environmental conditions, it is difficult to calculate the corrosion rates in most cases.
A 2007 study supported by the Transportation Research
Board on the rail base corrosion detection and prevention
suggests that the steel used in the fabrication of rails can
hold up to the effects of the environment (galvanic corrosion). However, dc significantly affects the corrosion rate and
makes the rails less corrosion resistant [6]. For the reliability
and safety of the public infrastructure, the productivity of
systems, the minimization of the impact on the environment, and economic competitiveness, it is essential to
understand the fundamental means that cause corrosion
and to find the most effective options for corrosion mitigation along with principles of regular inspection techniques.
There are many forms of corrosion, depending on the
type of metal, the surrounding environment, and the
length of exposure to the environment; however, this
IEEE Electrific ation Magazine / S EP T EM BE R 2 0 1 4

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2014