Corrosion Likelihood of Uncoated Metals

J/ = anodic partiai current density ). Jq= cathodic partial current density /g = total anodic current = total cathodic current 

Estimation of corrosion likelihood results from consideration of the characteristics of the soils and of the installed object, which are tabulated in Table 4-1 for nonalloyed and low-alloy steel products. Rating numbers, Z, are given according to the data on individual characteristics from which a further judgment can be made using the sum of the rating numbers. 

The sum reflects the corrosion likelihood of objects without extended cells as in Fig. 4-3b. This value also characterizes the class of soil, depending on which type of pipeline coating is selected [16]. The sum B, shows the corrosion likelihood of objects with extended cells as in Fig. 4-3c. This indicates that, in the case of extended objects, the class of soil is by itself not sufficiently informative. 

Objects with extended concentration cells can be individual lengths of pipeline and storage tanks if the makeup of the soil over the surface changes. The distance between anodic and cathodic areas can lie between a few centimeters and a few kilometers. 

The sum can only be obtained with buried objects and provides information on anodic damage through cell formation as in Fig. 4-3d. More detailed considerations can provide information on whether preferential anodic or cathodic regions are formed and how active they are [3,14]. 

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