Influence of Dynamic Current Fluctuation on Pipeline Corrosion Rate

In order to evaluate the corrosion risk of dynamic DC stray current interference, test coupons for free corrosion and cathodic protection were buried along a pipeline. The free corrosion potentials, cathodic potentials (switch-on and switch-off potentials), corrosion rates of the test coupons and soil resistivity at the buried points were tested. The influence of current fluctuation on corrosion rate was investigated by comparing the correlation between corrosion rate and soil resistivity, as well as the correlation between corrosion rate and cathodic protection parameters. The results show that the measured corrosion rates were generally higher than the evaluation results based on soil resistivity. The corrosion rates were increased by dynamic stray current. A parameter of dynamic stray current fluctuation intensity I_f was defined. The influence of dynamic DC stray current fluctuation on the effectiveness of cathodic protection was about 0.06I_f. According to the polarization potential difference and I_f, the total equivalent corrosion current was calculated by Tafel formula. The Pearson correlation coefficient between the current and the measured corrosion rate was as high as 0.97. The sum of the polarization potential difference and 0.06I_f can be used to evaluate the effectiveness of the pipeline cathodic protection under dynamic DC stray current interference.