Potential Attenuation and Anode Current Output Determination Alternatives for Marine Pipelines and Risers

Potential attenuation along a pipeline that is catholically polarized by multiple, equally spaced anodes is evaluated using three approaches boundary element modeling, a newly developed attenuation equation, and the classical equation of Uhlig, where the first two consider the net resistance to be comprised of electrolyte (anode), coating, and metallic path components, whereas the last approach neglects electrolyte resistance. It is demonstrated that results from the BEM analysis correspond to a first principles based projection of resistance change along a pipeline; and so results obtained by this method (BEM) are judged to be the most accurate of the three. Distinctions between the BEM and the newly developed attenuation equation, which is also first principles based, are discussed in terms of assumptions that are made in arriving at a closed form solution to the latter. The Uhlig equation is judged to be the least accurate of the three and to be non-conservative. While the closed form solution for the newly developed equation projects a potential attenuation that is non-conservative, the corresponding anode current output is conservative. Based upon this, a protocol for design of galvanic cathodic protection systems upon marine pipelines is proposed.