Research on the Cathodic Protection and Corrosion Behaviour of Box Culverts for Crossing Pipeline

Box culverts are usually used in the construction of long-distance pipelines crossing rivers and highways. Compared with the main pipe outside the box culvert, it is difficult to measure the potential of the pipe inside the box culvert. The steel reinforcement structure of the box culvert may absorb the cathodic protection current so that the cathodic protection potential of the pipe in the box culvert is insufficient, which will bring the risk of corrosion to the pipeline in the crossing section. To investigate the potential distribution law and corrosion characteristics of the pipeline in the box culvert, the experimental device for pipeline crossing box culverts was built in the laboratory to test and compare the cathodic protection potential and corrosion rate of pipelines entering, inside, and outside the box culverts under two working conditions of short circuit and non-short circuit between pipelines and the box culverts. The shielding calculation of box culverts was conducted using simulation software, and the cathodic protection shielding effect of box culverts on pipelines was ultimately explored. Results showed that cathodic protection inside the box culverts met established criteria and corrosion risk was minimal in the absence of a short circuit between the box culvert and pipelines. Conversely, when a short circuit between the box culvert and pipelines occurred, the cathodic protection potential of pipelines inside the box culverts fell below the criterion due to the current shielding effect of the box culvert, thereby increasing the corrosion risk. Under such circumstances, an increase in the output current of the rectifier is necessary to mitigate the risk of corrosion of pipelines inside the box culverts.