## 3 Stray Current Corrosion Morphology, Measurement Method, and Influencing Factors
### Factors Affecting Stray Current Corrosion
#### 3.4.2 Electrical Factors  
In terms of stray current corrosion in DC systems, research has found that factors that affect corrosion include the average track voltage in the system, the magnitude of the traction current, the applied voltage, the insulation of the track, the design of the grounding system, the distance from the interference source, and the interference cycle. Among them, the size of the traction current, the insulation of the track, and the design of the grounding system have an important impact on the magnitude of the stray current. Many scholars have studied this. [PERSON] and others [67] found through field tests that the main factors affecting DC stray current corrosion include the size of the traction current, the insulation of the track, and the resistivity of the soil. [PERSON] et al. [68] used multiphysics models and electrochemical methods combined with finite element simulation to study the impact of buried pipeline corrosion under different traction current intensities in DC traction systems. The study found that higher traction current intensity will immensely increase the corrosion rate. Corrosion mainly appears in the anode area in pipelines, especially near the track; thus, corrosion is more serious here. [PERSON] [69] used a combination of numerical simulations and field tests to study the impact of average track voltage on stray current corrosion of buried pipelines in a DC-electrified railway system. They found that the larger the average track voltage affected by stray current, the greater the intensity of current interference. [PERSON] and others [70] proposed an approximate reference electrode method combined with simulation to study the influence of dynamic DC stray current interference on buried pipelines under different applied voltage conditions in the soil. They found that applied voltage and burial depth exert a stronger influence on corrosion. [PERSON] [71] et al. studied the interference of X56 pipeline steel by stray currents and found that the higher the applied voltage, the closer the stray current is to the pipeline, and the greater the impact of corrosion on the buried pipeline. The factors influencing AC traction systems are quite different from those influencing DC systems. They include AC current frequency, current direction, waveform, and potential fluctuation. Compared with the constant current flow in DC systems, AC systems have frequency characteristics. [PERSON] [72] studied the corrosion behavior of X60 pipeline steel under the influence of AC currents of different frequencies (10-200 Hz). The study found that when the AC current frequency increases, the corrosion potential of X60 steel shifts positively, the anode current density decreases, and the rate of corrosion by the stray current is greatly reduced. [PERSON] et al. [64] conducted an experimental study on the corrosion behavior of X65 steel under different AC current frequencies and densities. By adjusting different current densities and frequencies, they found that when the current density increases, the corrosion potential of X65 steel shifts negatively, making the corrosion more serious. A higher current frequency will shift the corrosion potential positively, shortening corrosion time and reducing corrosion rate. Regarding the influence of current direction, [PERSON] et al. [73] believed that the asymmetry of the direction of the AC current is the key factor leading to the increase in corrosion rate. The influence of the change in stray current direction on cathodic protection was analyzed by modeling. The change in the current direction reduces the protection performance of the cathodic protection system and increases the risk of corrosion. [PERSON] et al. [74] found, through stress corrosion testing and simulation of the protection system of the cathodic system, that the corrosion of X80 steel is rapidly aggravated when the current direction is repeatedly switched, which has a huge impact on the cathodic protection system. [PERSON] et al.