Bimetallic corrosion protective measures

Protective measures against bimetallic corrosion should ideally start before the particular installation or equipment is built . Reference should be made to tables showing compatibility of metals, alloys and non-metallic materials (5 Table 1.25) and to the literature. However, it must be emphasised that the environment obviously plays a most important role in bimetallic corrosion, and that there are a number of situations in which apparently incompatible materials in contact can be used without adverse effects. 

In the previous case, it was a question of a type of bimetallic corrosion without electrical contact between the metals involved. The process initially is difficult to understand it is, however, easy to understand if one considers it as a battery with an external short circuit caused by an electrolyte behaving in the same way. The results of measurements on a model and the action of cathodic protection are described in Ref. 23. 

Contact with steel can accelerate attack on Al, but in some natural waters and other special cases, Al can be protected at the expense of ferrous materials, particularly when the Al is "passive." Titanium appears to behave in a similar manner to steel. Stainless steel in contact with Al may increase attack on Al, notably in seawater or marine atmosphere, but the high electrical resistance of the two surface oxide films minimizes bimetallic effects in less aggressive environments. Where Al is coupled to copper, or exposed to metallic copper contamination (such as in water systems), corrosion of the Al is very rapid. This is because Cu is particularly efficient at supporting cathodic reactions (e.g., oxygen and water reduction). Limiting cathodic currents measured for pure copper are reported to be in the vicinity of 1.5 mA cm , whereas limiting currents on pure Al are three orders of magnitude lower (0.5-1 pA cm- ) [52]. 

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See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

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