## 4 Corrosion Protection Measures
### Cathodic Protection
#### 4.2.2. Impressed Current Method of Cathodic Protection  
The forced current method involves directly applying a cathode current from an external direct current to the protected metal to polarize the cathode to achieve cathode protection. As shown in Figure 5, It consists of an auxiliary anode, reference electrode, DC power supply, and related connecting cables. The function of the auxiliary anode is to send the protective current to the electrolyte to flow to the protective body. In addition to external coating, cathodic protection is also a common measure for effectively preventing stray current interference in long-distance pipelines, but it is often used in combination with coatings; for example, impressed current cathodic protection is often used as the main method for regional cathodic protection and sacrificial anode protection is used as the auxiliary method for combined cathodic protection. [PERSON] [107] found that after the existing impressed current protection disappeared, the protected steel still showed no signs of corrosion for a certain period of time. This indicates that ICCP has the characteristic of continuous corrosion prevention. [PERSON] [108] found that the corrosion evaluation of the ICCP system in seawater was not similar to that of other areas due to the influence of the tide and splash zone of seawater. The ICCP system has a prominent protection effect on pipelines, but it is not without defects. For instance, impressed current cathodic protection is also effective. According to [PERSON], [PERSON]'s study [109; 110], the negative potential in the range of \(-850\) mV to \(-1.12\) V has the best effect on the prevention and control of stray currents. When the protection voltage is lower, the cathodic protection system often has a poor effect. However, when the voltage is too high, hydrogen evolution reactions occur easily, resulting in changes in the element composition and grain size of the pipe following hydrogen embrittlement and hydrogen damage (SCC). Residual stress concentration at corrosion pits also occurs more easily, leading to significant reductions in mechanical properties, thus degrading the mechanical properties of the metal [111]. Additionally, SCC has been identified as one of the major failures of pipeline steel in humid environments, resulting in cracking of high-pressure gas transmission pipelines and serious  
Figure 4: Schematic diagram of the new coating technology with anti-corrosion protection. economic losses and disasters. [PERSON] [112] found that in the decommissioned pipeline, the degraded X60 steel showed higher resistance to SCC in comparison with the degraded X52 steel. [PERSON] [113] found that AC and CI- have synergistic effects on metal corrosion. Taking X80 pipeline steel as the research object, he found that the fracture had obvious brittle fracture characteristics, and the preliminary analysis was the embodiment of the combined action of anodic dissolution and SCC. This is because after H\({}^{+}\) enters the surface of pipeline steel to obtain electrons, the generated gas often brings nonmetallic substances back to the surface of the pipeline, thus causing hydrogen-induced cracking of the pipeline or peeling of the coating. In addition, the ICCP system is affected by various complicated factors, so there may be inaccurate adjustments in some cases. For example, in areas of southwest China [114] with large soil displacement and frequent surface activities, buried pipelines are vulnerable to stress corrosion caused by soil displacement [115]. Pipelines in silty soil under salt-temperature coupling environments [116] are vulnerable to stronger corrosion than those in the interior. Pipelines in some humid areas are also vulnerable to microbial corrosion; however, with the development of pipeline intelligent equipment, intelligent ICCP equipment is emerging. [PERSON] [6] aimed to develop an ICCP system that integrates real-time monitoring and intelligent adjustment of the value of cathodic protection current potential.