Materials Performance

DEC 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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35 NACE INTERNATIONAL: VOL. 53, NO. 12 MATERIALS PERFORMANCE DECEMBER 2014 The Influence of a Grounding System on Cathodic Protection FIGURE 4 (a) Impact of grounding material on CP, (b) infuence of the relative position between grounding and pipeline position on CP, (c) infuence of the buried depth of grounding on CP, and (d) infuence of the length of grounding body on CP. (a) (c) (b) (d) A schematic diagram using the same number of anodes but adding grounding to the pipelines is shown in Figure 7(a). The result of this simulation with grounding is shown in Figure 7(b). With the grounding network in place and the anode configura- tion unchanged, the P/S potentials of the buried pipelines were between –611 and –646 mV CSE , roughly 300 mV more positive, which means a loss of effective CP. In order to restore effective CP for the grounded piping, the number of anodes was increased and their positions were changed to increase and redistribute the protective current. The modified anode configuration follows the grounding paths as shown in Figure 8(a). The result of this simulation is shown in Figure 8(b). The P/S potentials of the buried and ground ed pip elin es were improved to between –869 and –998 mV CSE , indicating that effective CP had been restored. A com- parison of Figures 6(a) and 8(a) demon- strates that numerous additional anodes were required to obtain effective CP with grounding vs. without grounding. Installing sacrificial anodes is just one solution. An alternative might be impressed current CP. In this example, the impressed current requirement for pipe with ground- ing would be dozens of times the amount needed for piping without grounding. Conclusions The effect of grounding conductors on pipeline CP was studied using the BEM, resulting in the following conclusions: • When comparing the experiment and simulation results, the mathematical model of the impressed current CP system was found to be representa- tive. The BEM modeling proved to be highly ef ficient for simulating CP potential distribution and for CP design in an oil station.

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