Stray-current corrosion avoiding

In soils, stray current corrosion can be caused by close proximity to other buried metal systems that are being protected by an impressed current cathodic protection system. These stray currents can leak onto a buried aluminum structure at one point, then off at another (where corrosion occurs), taking a low-resistance path between the driven buried aiwde and the nearby structure being protected. (Totmnon bonding of all buried metal systems in close proximity is the usual way to avoid such attack (Ref 39 and 40). 

Stray current flowing along a pipeline very often will not cause damage inside the pipe, because of the high conductivity of the electric path compared with the electrolytic path. The damage occurs when the current reenters the electrolyte and will be localized on the outside surface of the metal. If the pipe has insulated joints and the stray current enters the internal fluid, localized corrosion on the internal side of the pipe will occur. The best solution to avoid this mode of corrosion is the electrical... 

Even in the absence of chlorides, if the current flows at a sufficiently high density for enough time to acidify the anodic area, corrosion of the iron can be sustained by potential differences considerably lower than those that are necessary for its initiation. If the concrete is carbonated, current density and times required for acidification of the anodic zones are obviously reduced however, these are quite exceptional conditions, which may in fact not occur in the case of stray currents but occur only in conditions of stationary interference currents that the design must plan to avoid. 

Rebar continuity is essential to avoid stray currents that can accelerate corrosion. Figure 7.19 shows how an isolated rebar between the anode and the cathode will be cathodic where the current enters the steel and anodic where it exits. This will accelerate corrosion at the anodic site. Although there are few serious cases identified in cathodic protection systems, this is a greater concern for realkalization and desalination systems where the charge density is higher. 

Cleanliness. Keeping the battery clean will minimize corrosion of cell post connectors and steel trays and avoid expensive repairs. Batteries commonly pick up dry dirt, which can be readily blown off or brashed away. This dirt should be removed before moisture makes it a conductor of stray currents. One problem is that the top of the battery can become wet with electrolyte any time a cell is overfilled. The acid in this electrolyte does not evaporate and should be neutralized by washing the battery with a solution of baking soda and hot water, approximately 1 kg of baking soda to 4 L of water. After application of such a solution, the area should be rinsed thoroughly with water. 

It is common to add up to 3% calcium chloride to concrete, in order to accelerate setting and thus avoid freezing in the cold of winter. This leads to a substantial decrease in the resistivity of concrete adding 3% calcium chloride leads to a drop in resistivity by a factor of 1000. Since calcium chloride is hygroscopic, it may keep the concrete from drying. In the presence of humidity, the conductivity of the medium increases, and electrical corrosion reactions are facilitated. In the absence of humidity, stray currents and contact with steel, adding chlorides does not significantly modify the resistance of aluminium in concrete [7]. 

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