A first principles based equation for potential attenuation along a marine pipeline or riser that was cathodically polarized by multiple, equally spaced, identical galvanic anodes and that incorporated the electrolyte (anode), coating, and metallic path resistances, as well as the pipe polarization resistance, was derived. Finite difference method (FDM) solutions for this equation showed that the potential profile consisted of a relatively abrupt polarization decay within the first several meters of an anode and an essentially constant potential beyond this for cases where anode spacing was ca < 1 km (this distance varied with pipe and anode dimensions, properties, and exposure conditions). For anode spacings greater than this, metallic path resistance became important such that a potential gradient resulted along the entire pipe length. Comparison of the FDM solutions for the case of a pipeline of typical dimensions and marine exposure conditions with results from boundary modeling (BEM) indicated excellent agreement between the two for situations where the metallic resistance was negligible. For cases where this term was not negligible (relatively large anode spacings), the FDM solutions were more accurate since BEM did not incorporate metallic path resistance. The potential attenuation projected by the classical equation of Uhlig was shown to be nonconservative compared to the FDM and BEM solutions because of its failure to consider the electrolyte component of circuit resistance. Anode current output determinations based upon the derived equation and BEM were shown to be in excellent mutual agreement. It was concluded that the derived equation has utility for design of pipeline cathodic protection systems and for analysis of data therefrom, particularly in cases where anode spacing is sufficiently large that metallic path resistance in non-negligible.


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    Title :

    A new equation for potential attenuation and anode current output projection for cathodically polarized marine pipelines and risers


    Additional title:

    Eine neue Gleichung für Potentialabschwächung und Anodenstrom-Ausgangsleistung an kathodisch polarisierten Rohrleitungen und Steigrohren in Meerwasser


    Contributors:

    Published in:

    Corrosion, Houston ; 56 , 4 ; 350-360


    Publication date :

    2000


    Size :

    11 Seiten, 9 Bilder, 1 Tabelle, 10 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English