Field Testing and Evaluation on Cathodic Protection of Horizontal Directional Drill Pipe Sections

Abstract Cathodic protection (CP) is critically important for horizontal directional drill (HDD) pipe section since the integrity of coating is usually damaged due to the pull-back of pipeline during installation. Unfortunately, CP criteria and field testing method for CP parameters of HDD pipe section have not reached a consensus so far. In this work, a field testing method was proposed for evaluating CP of the whole HDD pipe section, with the buried depths varying from 3 meters to tens of meters. The results show that the proposed field testing method can measure potential of HDD pipe section passing through different depths. When buried depth reaches 25 meters, the measured free corrosion potential can be more negative than the traditional CP criteria of “-850 mV CSE” due to the significant decrease of oxygen. Besides, oxygen concentration cell between pipe at shallow depth and deep depth may exist. In order to investigate the effectiveness of CP criteria of -850 mV CSE polarized potential on HDD pipe section, weight loss tests on mild steel coupons under different CP levels and oxygen levels were conducted. The experimental results show that the measured free corrosion potential shifts negative with decreasing oxygen and oxygen concentration cell is confirmed. The presence of SRB will accelerate corrosion significantly. CP criteria of -850 mV CSE polarized potential is not enough in de-aerated environment, SRB environment and oxygen concentration cell. It should be more negative than -950 mV CSE.