Effect of Iron Ion on the Evaluation of Buried-Steel Pipeline Corrosion

The effect of iron ions assessing the corrosion status of buried-steel pipelines was investigated in this work. The results show that the iron ions significantly affect the accuracy of the potential determination and further affect the evaluation of pipeline corrosion status. As the iron ions concentration increase, more negative shifts of the potential are observed gradually. To evaluate this effect in the actual case, field tests were also conducted in areas near Tongzha and Panyuan Road, Chongming District, Shanghai, PR China, where the iron content is rich. It was found that compared to the most negative marginal value of current cathodic protection standards ($-1.200\mathrm{V}$ ), the on-potential and off-potential of test points 1 and 2 shift to the negative, and the margin of average shifts reach $-0.080\mathrm{V}$ and $-0.030\mathrm{V}$ , respectively, indicating that the anticorrosion coating of the measured steel pipe segment has been destroyed. However, onsite inspection results found that the coating of the pipe segment has no corrosion failure. Current standards are invalid to assess the corrosion failure status for steel pipelines buried in soils containing iron ions, and they need to be revised.