Localized corrosion dezincification

Localized corrosion, which occurs when the anodic sites remain stationary, is a more serious industrial problem. Forms of localized corrosion include pitting, selective leaching (eg, dezincification), galvanic corrosion, crevice or underdeposit corrosion, intergranular corrosion, stress corrosion cracking, and microbiologicaHy influenced corrosion. Another form of corrosion, which caimot be accurately categorized as either uniform or localized, is erosion corrosion. 

Dezincification As either plug dezincification (localized corrosion) or layer dezincification (general corrosion) and refers to zinc (Zn) being selectively leached out of brass. It can be prevented either by reducing the Zn content to below 15% or by the addition of trace amounts of inhibiting elements such as arsenic (As)... 

In addition to ductile iron and PVC, copper and lead are used in pipes, and brass in fixtures and connections. Lead is released because of uniform corrosion. Copper is also released because of uniform corrosion, localized-attack cold water pitting, hot water pitting, MIC, corrosion fatigue, and erosion-corrosion. Lead pipes and lead-tin solder exhibit uniform corrosion. Brass corrosion includes erosion-corrosion, impingement corrosion, dezincification, and SCC. The direct health impacts are because of increased copper, lead, and zinc concentrations in the drinking water. Mechanical problems because of corrosion include leaks from perforated pipes, rupture of pipes, and the loss of water pressure because of blockage of pipes by corrosion products. 

P + Pi brasses of similar composition (Cu—38 wt.% Zn and Cu—41 wt.% Zn, respectively), it has been concluded that this is not simply due to an increased Zn concentration in the p phase, but is likely to reflect the structural differences of hoth phases [67]. Other factors that stimulate the dezincification of both O - and a p brasses are the presence of chlorides, high concentrations of CuCl2 ions, stagnant environments, differential aeration cells and elevated temperatures. In chloride solutions, such conditions are typically encountered at a later stage of corrosion when mass transport restrictions by a deposit, corrosion product, or crevice have heen established and create a local environment, in which the copper in the brass is nearly in equilibrium with CU2O, CuCl, and accumulated CuCl2 anions [68,69]. Experimentally, the necessity... 

Brass alloys of copper can be subject to deallo)dng (dezincification), a type of corrosion in which the brass dissolves as an alloy and the copper constituent redeposits from solution onto the surface of the brass as a metal in a porous form. The zinc constituent may be deposited in place as an insoluble compound or carried away from the brass as a soluble salt. The corrosion can take place uniformly or locally. The latter, called plug-type... 

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