## 3 Stray Current Corrosion Morphology, Measurement Method, and Influencing Factors
### Factors Affecting Stray Current Corrosion
#### 3.4.3 Other Factors  
(1) Stress factors  
Among the many factors that cause stray current interference of pipelines, stress is an important factor that cannot be ignored. The stress concentration area of the pipeline is a fragile area that is very susceptible to stray current interference. Common stress concentration areas include the welds, joints, and pipeline turns. Such areas are more susceptible to the influence of electrochemical reactions. Over time, cumulative effects occur, and the corrosion rate continues to increase. Corrosion in high-stress areas gradually becomes serious, and corrosion-induced cracking occurs and continues to expand. [PERSON] and others [78] studied the cumulative corrosion effect of stray currents in the subway system with the finite element model combined with the influence of mechanical stress. The study found that the distribution of stray currents on the track system is uneven. During the long-term operation of the system, stray current interference continues to accumulate in areas where stress is concentrated, causing damage to local areas and significantly increasing the corrosion rate [79]. (2) The quality of the anti-corrosion layer and the effectiveness of the cathodic protection system Anti-corrosion coating and cathodic protection systems are both important measures for pipeline anti-corrosion. The high quality and integrity of the coating and the effectiveness of the cathodic protection system are important factors in slowing down corrosion. In terms of the quality and integrity of the anti-corrosion coating, [PERSON] et al. [80] simulated the corrosion behavior of X80 steel in 3.5% sodium chloride solution through electrochemical experiments. Through SEM analysis, they found that the protective layer of the pipe showed debonding behavior under the influence of stray currents, and the corrosion in the debonding area intensified with the increase in current density. [PERSON] [24] studied the corrosion effect of AC stray current on X70 pipeline steel at the polyethylene coating defect by electrochemical method. The study found that when the coating defect area is small, the depth of the corrosion pit is deeper, and the corrosion current density is higher. The stray current corrosion in the area with larger coating defects is more severe. This study shows that the size of the coating defect will also have a corresponding effect on corrosion. Some scholars have introduced detection methods, such as CIPS and DCVG, for pipeline anti-corrosion coating damage and evaluated pipeline corrosion in different areas based on field data. Studies have found that coating damage will intensify anode dissolution and cause local potential negative shifts in this area, accelerating the corrosion process. Additionally, coating damage will also influence the effectiveness of the cathodic protection system. The coating at the damaged location will prevent the current from being evenly distributed on the surface of the pipeline, making the buried pipeline more susceptible to stray current corrosion [81]. In terms of the design of the cathodic protection system, [PERSON] [82] evaluated the design of the cathodic protection system by simulating the interference of high-voltage DC electrodes on buried pipelines and found that the layout of the insulating flange greatly affected the effectiveness of the cathodic system protection. An unreasonable layout made it easier for stray current to return to the ground, destroying the original current path and forming new corrosion points. Reasonable distribution can prevent the spread of stray current and reduce its flow into the protected area. [PERSON] and others [83] reviewed the impact of AC stray current on the cathodic protection system and believed that the potential fluctuation of AC current makes its interference area larger, while the potential control range of the cathodic protection system cannot cope with the impact of its fluctuation.