# Influence of Stray Current on Fastening System Components in Urban Railway Tracks
## 1 Introduction
\begin{table}
\begin{tabular}{c c} \hline
**Study** & **Main Objective of Conduced Study** \\ \hline [PERSON] et al. [22] & Simulating the stray current corrosion of buried pipeline using COMSOL software \\ \hline [PERSON] et al. [25] & Experimental study of stray current corrosion on steel pipeline \\ \hline [PERSON] et al. [26] & Analysis of stray current distributing model in the subway system \\ \hline [PERSON] and [PERSON]. [27] & Simulation model for evaluating rail potential and stray current \\ \hline [PERSON] et al. [28] & Analysis of rail corrosion, including corrosion forms, protection and detection technologies \\ \hline [PERSON] et al. [33] & Analysis of stray current corrosion of buried metal under different content of salt \\ \hline [PERSON] [34] & Stray current modelling on DC traction systems \\ \hline [PERSON] et al. [35] & Analysis of rail-to-earth resistance measurement in traction supply system \\ \hline [PERSON]; et al. [36] & Analysis of stray current distribution characteristics during train operation and impact \\  & of the stray current on buried pipelines \\ \hline [PERSON] et al. [37] & Analysis of rail potential and stray current in railway electrification system \\ \hline [PERSON] et al. [38] & Analysis of rail potential distribution in metro system using CDEGS software \\ \hline [PERSON] [39] & Reviewing electrical quantities that characterize stray current, stray current protection \\  & and corrosion phenomena \\ \hline [PERSON] et al. [40] & Detection method and analysis methodology of dynamic stray current effects on \\  & underground pipelines \\ \hline \end{tabular}
\end{table} 
Table 1: Review of studies focusing on stray current. Because the electrical resistance of the rail depends on the rail cross section, the resistance increases during exploitation owing to rail head wear and cross-sectional thinning due to the corrosion process. According to [34], rail wear can be caused by increasing the rail electrical resistance by 19%. According to [35], the rail-to-ground resistance is required to control the stray current. The resistance depends on the type of track and rail insulation [17]. For tracks with continuously supported and fastened rails, where the rails are fully insulated with an elastic material, a high rail-to-ground resistance is achieved and stray current is prevented. For tracks with discretely supported and fastened rails, it is very difficult to ensure sufficient resistance between the rail and ground; therefore, stray currents can greatly affect the track and metal objects near the track. Because the type and properties of fastening systems are selected depending on the required elasticity of the track, planned traffic load, and type of rail [48], the electrical resistance of the fastening system is not defined in the specifications. According to [36; 42], even perfect rail insulation lasts only a few years if the tracks are not properly maintained; therefore, rail-to-ground resistance depends on the electrical resistance of the concrete base layer and the soil, which can vary greatly depending on the location of the tracks. Consequently, the rail-to-ground resistance values provided in the guidelines vary across countries for the same type of track construction, as shown in [49; 50]. The corrosion rate and stray current are higher in closed urban tracks because it is very difficult to provide adequate drainage, and the tracks dry very slowly. Thus, the remaining water accelerates the corrosion and stray current. Urban tracks embedded in lanes shared by road vehicles (Figure 1a,b) are also exposed to chlorides that are used in winter to prevent icing of the pavement [29]. These chlorides dissolve in water and enter the tracks [30], which results in a decrease in the electrical resistance between the rail and ground. Compared to the mass of the rail and the metal parts of the fastening system, stray current corrosion does not cause a significant loss of material on the track, but the deterioration caused by stray current is localized.