Mathematical models were developed to predict cathodic protection (CP) requirements for coated pipelines protected by parallel anodes. This work was motivated by the need to estimate current and potential distribution on a pipe when anodes are placed nearby or when discrete coating holidays expose bare steel. The mathematical model solves Laplace's equation for potential with boundary conditions appropriate for the pipe being protected, the anode, and any region through which current does not pass. The current density on bare steel was assumed to be composed of contributions from corrosion, reduction of dissolved oxygen, and evolution of hydrogen. Kinetic parameters were obtained from independent experiments. The anode was assumed to have a constant potential, and current was allowed to flow through the coating under the assumption that the coating is a highresistance ionic conductor. A boundary element technique coupled with Newton-Raphson iteration was used to solve the governing equations for two-(2-D) and three-dimensional (3-D) configurations. Results showed good agreement with experimental values and can be used to assess viability of CP designs. KEY WORDS: anodes, boundary elements, cathodic protection, coatings, films and film formation, holidays, modeling, pipelines and line pipe steel, polarization curves 0010-9312/97/000063/$5.00+$0.50/0 © 1997, NACE International FIGURE 8. CP current delivered to a coated pipe with a 5.67-cm (2.25-in.)-diam circular holiday calculated by a 2-D BEM model. Polarization resistance is negligible compared to the ohmic resistance at high electrolyte resistivities.

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Calcium magnesium acetate (CMA) is a term used to describe the reaction product of acetic acid and dolomitic limestone. This product is a mixture of calcium acetate and magnesium acetate and hes been identified as a possible deicing chemical to replace chloride-containing chemicals such as sodium chloride and calcium chloride. The Federal Highway Administration has sponsored work to determine the corrosive behavior of CMA on bridge structural materials and steel in concrete.Electrochemical tests ware conducted in commercial and reagent-grade CMA solutions of 0.5 to 20 wt%. Anodic and cathodic polarization behavior and corrosion rates were determined by the polarization resistance technique.Polarization scans showed that steel can exhibit activepassive behavior in both commercial-and reagent-grade CMA solutions. Reverse polarization scans indicated an unusual electrochemical behavior occurred with three current reversals in commercial-and reagent-grade CMA solutions of 2 wt% and higher. A current reversal occurred, followed by a cathodic loop; then a second current reversal occurred. An anodic current loop followed this second current reversal, which was in turn followed by third current reversal.The double-loop behavior was determined to be dependent on CMA concentration and upon the presence of carbon dioxide. It is proposed that carbon dioxide is formed as a consequence of an electrochemical reaction involving the acetate ion. The carbon dioxide dissolves in the solution and in turn results in precipitation of insoluble carbonates at cathodic sites on the steel surface. The total exchange current is lowered by the covering of cathodic sites and results in a shift in the corrosion potential in the cathodic direction. When the transient corrosion potential becomes more cathodic than the initial corrosion potential, then net anodic current will be drawn during the reverse anodic polarization scan. The double-loop behavior is then observed.KEY WORDS: calcium magnesium acetate, electrochemical behavior, steel INTR O D UCTI O NCalcium magnesium acetate (CMA) is a jargon name used to describe the reaction product of acetic acid and dolomitic limestone. This reaction product is a mixture of calcium acetate and magnesium acetate that has been identified as a possible replacement deicer for sodium chloride and calcium chloride deicers.' To develop an understanding of the electrochemical behavior and corrosivity of CMA to A36 (UNSt' ) K02600) steel, electrochemical testing was conducted in solutions of reagent-and commercial-grade CMA at concentrations of 0.5 to 20.0 wt%.In an earlier study by Luster, 2 electrochemical tests on steel