An indoor corrosion simulation experiment device was built to explore the influence of dynamic AC interference on the corrosion behavior of pipeline steel under different cathodic protection (CP) levels. When the interference time in each interference cycle is 350 s, the dynamic AC corrosion rate was comparable to the steady AC corrosion rate. For JAC of 30 A·m-2, the corrosion rate of the specimen can be controlled below 0.0254 mm·y-1 when the CP current density is higher than 0.06 A·m-2. As JAC is greater than or equal to 100 A·m-2, with the increase of the cathodic protection current density, the corrosion rate of the specimens decreased firstly, then increased and decreased again. In this paper, the real-time AC/DC potential on the surface of the specimen is monitored, combined with Pourbaix diagram and the evolution of corrosion product film, the dynamic AC corrosion mechanism under different cathodic protection levels was explored.

In recent years, due to the large-scale construction of wind power and shore power projects, the amount of submarine high-voltage AC cables has been increasing year by year, and they often form a "common corridor" in parallel with adjacent submarine pipelines, resulting in AC interference on pipelines. A lot of research has been carried out on the AC interference law of buried pipelines onshore. However, there is a lack of discussion on the AC interference suffered by submarine pipelines from high-voltage AC cables.How to understand the AC interference law of high-voltage AC cables to submarine pipelines and determining the safe distance has become an urgent demand in practical production. Based on this, this paper established a calculation model for AC interference suffered by submarine pipelines from high-voltage AC cables on through CDGES software. Through simulation calculation, the influence laws of many factors such as parallel distance between AC cables and pipelines, parallel length, cable load current, anticorrosive coating resistivity, and longitudinal pipeline resistance per unit length on AC interference parameters of pipelines were investigated. It was found that the degree of AC interference increases with the increase of the anticorrosive coating resistivity, the load current, and the longitudinal pipeline resistance per unit length, as well as the decrease of the parallel interval.However, with the increase of the parallel length, the AC interference voltage and current density of the pipeline increase firstly, then decrease, and at the end remains unchanged, and it was found that there existed the parallel length with the maximum AC interference and the saturation parallel length with unchanged AC interference. Based on the principles of electromagnetic induction and AC circuits, the main reasons for the parallel length with maximum AC interference and the saturation parallel length were analyzed in this paper. The safe distances avoiding AC corrosion under different parallel lengths and load currents were discussed, which can provide a reference for the evaluation of AC interference of submarine pipelines and the selection of submarine routing.