## 3 Stray Current Corrosion Morphology, Measurement Method, and Influencing Factors
### Factors Affecting Stray Current Corrosion
#### 3.4.3 Other Factors
It is proposed that the cathodic protection system should adopt a higher potential control range and add decoupling devices to adjust the frequency of AC current to reduce its interference. Moreover, [PERSON] believes that there are multiple sources of stray current, and the superimposed stray current will make it difficult for a single cathodic protection method to cope with it. The impact of each stray current source should be fully evaluated, and a multi-layer protection strategy should be specified. Interactive monitoring, dynamic monitoring, and timely adjustment to the cathodic protection system should be undertaken. [PERSON] et al. [74] believe that the design of the cathodic protection system needs to consider the mechanical stress factors of the pipeline. The stress concentration area and the damaged area of the anti-corrosion layer are very weak, and conventional cathodic protection cannot achieve the ideal effect. It is proposed that the design of the cathodic protection system should be combined with the stress monitoring system to provide additional current protection for the stress concentration area and improve the corrosion resistance of the pipeline. Through the research of the above scholars, it is shown that damage to the anti-corrosion layer and the effect of the cathodic protection system will greatly affect the degree of corrosion of the pipeline by stray current. The cathodic protection system should be designed accordingly and more effectively according to the specific situation while ensuring the integrity and high quality of the anti-corrosion layer. (3) Pipe material factorsIn order to ensure the safety and stability of long-distance pipelines, more and more high-grade steels are being developed and applied. At present, the steels commonly used for oil and gas pipelines include X60, X65, X70, and X80. More advanced X100 and X120 steels are also being gradually developed and used. SMI announced the research results of X100 high-strength pipeline steel in 1988; by September 2002, TransCanada had successfully used X100 high-strength pipeline steel in the Saratoga test section of the WESTPATH project and achieved corresponding research results. In 1993, the Exon Corporation of the United States began to study X120 pipeline steel. In 1996, Exon Corporation cooperated with other companies to jointly promote the research and development of X120 pipeline steel. Canada included X100 steel in the CSAZ245.1-2002 standard [84] in 2002 and built a 2 km long X100 high-strength steel pipeline with a diameter of 914 mm in 2004. However, X100 and X120 pipeline steels have not been widely used due to manufacturing and cost reasons, and they are still in the research stage. Many scholars at home and abroad have studied the performance of different grades of steel, such as X60, X65, X70, and X80. These studies have shown that the overall corrosion resistance of the pipeline under the influence of stray current increases with the improvement of steel grade. At the same time, the higher mechanical strength of pipeline steel can better reduce the corrosion interference caused by complex interference environments. However, compared with low-strength steel, high-strength steel is more brittle and is susceptible to hydrogen embrittlement after stress concentration occurs in certain weak parts, making pipeline steel more prone to fatigue cracks. The corrosion resistance of different steels varies in complex current environments, and reasonable material selection and protection measures can reduce corrosion [85]. The environment, electricity, and some other factors, such as stress factors, have a corresponding impact on stray current interference. Further protection measures need to be taken against these influencing factors to reduce the interference of stray currents on pipelines in traction systems. Table 1 summarizes the factors influencing the stray current corrosion mentioned above.