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36 APRIL 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 4 Selecting the Number of Anodes The sacrificial anode system for the uncoated jacket was designed according to the DNV-RP-B401 criterion. 3 The CD for CP was 65 mA m 2 ; therefore, a total of 10 anodes would be required to protect the jacket for FIGURE 2 CD output of anodes contour plot (A·m –2 ) and protective CD contour plots (A·m –2 ) for the optimum design in the Persian Gulf. FIGURE 3 Anode positions and potential contour plot (V) for the optimum design in the Caspian Sea. a design life of one year. The sacrificial an o d e cur rent output wa s cal cul at ed through Ohm's law. The current output of anodes in the Persian Gulf and Caspian Sea, listed in Table 1, exceeded the anticipated current demand. Results and Discussion Optimizing the Arrangement of Anodes The objective of modeling this sacrifi- cial anode system was to achieve uniform potential distribution over the platform surfaces and uniform mass loss rate of the anodes. This design optimization of the system is important—it can reduce the maximum protection potential and corro- sion CD over the surface of the platform, and minimize the risk of sacrificial anode depletion before the end of their required design life, since some anodes may be con- sumed more quickly than others. 14 The anodes were distributed on sup- port tubes in an almost uniform manner in the optimum design. The optimum anode positions and the contour plot of potential distribution on the jacket in the Persian Gulf are shown in Figure 1. The potentials of the steel jacket are between –925 and –999 mV. The potentials are more negative in areas adjacent to the anodes, while the cathodic polarization is reduced along both the longitudinal direction and the cir- cumference. The optimum protective CD distribution plot on the jacket is shown in Figure 2. CD peaks are observed in areas adjacent to the anodes, while the protec- tive CD decreases exponentially to its mini- mum value in other areas. In some studies, 9 the anodic dissolution rate of iron often decreases with increasing protective CD. In this optimum design, the anodic dissolu- tion rate of the platform achieves its mini- mum value. The current flow in an equivalent elec- trical circuit, which represents the sacrifi- cial anode system with a cathode and a sac- rificial anode, is calculated using Ohm's law in Equation (9): 1,6 = + + i E – E R R R flow a c a c e (9) where i flow is the current flow in the equiva- lent circuit, which is proportional to the protective CD; E a and E c are the potentials associated with the anode and cathode, respectively ; R a is the resistance associated with an anode; R c is the cathode resistance; and R e is the electrolyte resistance. Regard- ing the distance between an anode and the cathode surface, the R e between an anode CATHODIC PROTECTION