Corrosion in Water and Steam

Extraneous anions in dilute chloride solutions act as pitting inhibitors by shifting the critical pitting potential to more noble values [4]. The following ions are effective in decreasing order nitrate chromate acetate benzoate sulfate. 

TABLE 21.1. Composition Limits for Some Wrought Aluminum Alloys  

In uncontaminated seawater in the tropical environment of Panama, commercially pure aluminum (1100) or 0.6% Si, 0.8% Mg, 0.2% Cu-Al alloy (6061-T) corroded at decreasing rates with time. After 16 years of exposure, the total weight losses were 67 and 63g/m, and the corresponding observed deepest pits were 0.84 and 2.0mm (0.033 and 0.079in.), respectively, for smaU-size test panels [5]. At the same location in fresh water, probably contaminated with heavy metals, the corresponding weight losses for 16 years were higher—347 and 103 g/m — and the deepest pits measured 2.8 mm (0.11 in.) each. 

The beneficial effect of cathodic areas can be explained [7] as one of anodic passivation or anodic protection of aluminum in the same manner as alloying additions or coupling of platinum or palladium to stainless steels or to titanium passivate these metals in acids (Section 6.4). 

At 500-540°C, the oxidation rate of pure aluminum in steam is appreciably lower than at 300-450°C [8], presumably because a more protective oxide film forms within the higher temperature range. 

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S. Kass. 1964. The Development of the Zircaloys in Corrosion of Zirconium Alloys, ASTM STP 3687, Philadelphia, PA American Society for Testing and Materials. D.E. Thomas. 1995. Corrosion in water and steam, in Metallurgy of Zirconium,... 

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