Cathodic protection rectifier anodes for iccp systems

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cathodic protection rectifier). Anodes for ICCP systems are tubular and solid rod shapes of various specialized materials. These include high siliconcast iron, graphite, mixed metaloxideor platinumcoated titanium or niobiumcoated rod and wires.Corrosion in passivated materialsPassivationis extremely useful in alleviating corrosion damage, but care must be taken not to trust it too thoroughly. Even a high-quality alloy will corrode if its ability to form a passivating film is hindered. Because the resulting modes of corrosion are more exotic and their immediate results are less visible than rustand other bulk corrosion, they often escape notice and cause problems among those who are not familiar with them.Pitting corrosionMain article: Pitting corrosionCertain conditions, such as low concentrations of oxygen or high concentrations of species such as chloridewhich compete as anions, can interfere with a given alloy's ability to re-form a passivating film. In the worst case, almost all of the surface will remain protected, but tiny local fluctuations will degrade the oxide film in a few critical points. Corrosion at these points will be greatly amplified, and can cause corrosion pitsof several types, depending upon conditions. While the corrosion pits only nucleateunder fairly extreme circumstances, they can continue to grow even when conditions return to normal, since the interior of a pit isnaturally deprived of oxygen. In extreme cases, the sharp tips of extremely long and narrow can cause stressconcentrationto the point that otherwise tough alloys can shatter, or a thin film pierced by an invisibly small hole can hide a thumb sized pit from view. These problems are especially dangerous because they are difficult to detect before a part or structure fails. Pitting remains among the most common and damaging forms of corrosion in passivated alloys, but it can be prevented by control of the alloy's environment, which often includes ensuring that the material is exposed to oxygen uniformly (i.e., eliminating crevices).Weld decay and knifeline attackMain article: Intergranular corrosionStainless steelcan pose special corrosion challenges, since its passivating behavior relies on the presence of a minor alloying component (Chromium, typically only 18%). Due to the elevated temperatures of weldingorduring improper heat treatment, chromium carbidescan form in the grain boundariesof stainless alloys. Thischemical reaction robs the material of chromium in the zone near the grain boundary, making those areas much less resistant to corrosion. This creates a galvanic couplewith the well-protected alloy nearby, which leads to weld decay(corrosion of the grain boundaries near welds) in highly corrosive environments. Special alloys, either with low carbon content or with added carbon "getters" such as titaniumand niobium(in types 321 and 347, respectively), can prevent this effect, but the latter require special heat treatment after welding to prevent the similar phenomenon of

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