Nickel, galvanic corrosion

Aluminum is not embrittled by low temperatures and is not subject to external corrosion when exposed to normal atmospheres. At 200°C (400°F) its strength is less than half that at room temperature. It is attacked by alkahes, by traces of copper, nickel, mercuiy, and other heaw-metal ions, and by prolonged contact with wet insiilation. It suffers from galvanic corrosion when coupled to copper, nickel, or lead-... 

Heat exchangers that utilize copper coils are potential candidates for galvanic corrosion due to dissolved copper salts interacting with the galvanized steel shell. This problem can be avoided by nickel plating the coils. The coils then can be separated from direct contact with the vessel via insulation. Also, it is preferable to conduct the water on the tube side of heat exchangers. 

It has been shown that chromium is virtually unattacked by the CASS test solution Nickel, on the other hand, is corroded at a substantial rate (about 0-072mm/y), the presence of the copper ions tending to maintain the nickel in an active state . Thus, in the CASS test (and in the Corrodkote test as well) accelerated galvanic corrosion of the nickel occurs at any discontinuities in the chromium layer. Good correlation between the results of the CASS test and the performance of plated parts in service has been reported . 

There is some evidence that nickel slag can be involved in the corrosion of iron and steel in the presence of moisture (probably galvanic corrosion). In Canada, where nickel slag is used in fill applications, it is common practice to provide a layer [typically 150 mm (6 in.) thick] of natural aggregate between ferrous materials and the slag.21... 

Aluminum is a soft, ductile, and relatively inexpensive metal. The surface of aluminum readily oxidizes in the air and water to form a highly resistant oxide film. This oxide film serves to make aluminum resistant to attack when used in environments containing sulfides, sulfur dioxide, carbon dioxide, and other corrosive gases. It is highly resistant to water-initiated corrosion, but is susceptible to galvanic corrosion by trace amounts of copper, tin, lead, nickel, or carbon steel. The reaction of aluminum in water to form Bayerite is shown in FIGURE 9-2. 

Corrosion. The tubes in the LTV evaporator were installed with Swenson rubber grommet packing commonly used for Karbate tubes in acid evaporators. This both insulated the tubes from galvanic corrosion and allowed nondestructive removal for weighing. Corrosion rates were estimated both from weight loss of the tubes and from International Nickel Co. test spools located both in the vapor space and immersed in the liquid in the blowdown tank. 

Special considerations in conductive applications, special conductive blacks must be employed in silver containing gaskets, galvanic corrosion is a problem, attention should be given to material with which diield is connected (potential difference), with zinc or aluminum casing nickel filled materials are preferred... 

Corrosion of Magnesium in Neutral and Alkaline Solutions Magnesium is highly susceptible to galvanic corrosion. Small amounts of impurities in the alloy can have a tremendous influence on the corrosion susceptibility. In Fig. 30, the influence of various elements is demonstrated. Small additions of copper, iron, nickel, and cobalt have an extremely negative effect on the corrosion resistance. The tolerance Kmit for iron is 0.015%, for nickel 0.0005%, and for copper 0.1% [35]. Because of the low solid solubility of these elements, they precipitate as inclusions. These act as active cathodic sites for the... 

E6.1. Predict the possibihty of galvanic corrosion in sea water for the following coupled pairs of alloys and metals (i) aluminum alloys and aluminum brass, (ii) cadmium and manganese bronze, (iii) zinc and tin, (iv) low alloy steel and stainless steel 410, (v) low alloy steel and stainless steel 430, (vi) nickel 200 and Ni-Cr-Mo-Cu-Si... 

E6.2. Predict whether or not galvanic corrosion will cause the following alloys to be subjected to leaching (i) carbon and carbon steel alloys in an oxidizing atmosphere, (ii) steel rivets in aluminum drain gutters, (iii) copper-nickel alloy in refinery condenser tubes, (iii) graphite fiber-reinforced aluminum composites, (iv) brass in water, (v) iron-chromium alloys, and (vi) carbon steel pipe in contact with the weld to stainless steel pipe. 

The corrosion rates for nickel (Icorr, Ni-Fe) and iron (Icorr, Ni-Fe) after galvanic coupling are calculated by substituting the corrosion potential of the iron-nickel galvanic couple Ecorr,coupie=— 0.185V vs. SHE in Eqs. (E6.7) and (E6.9), respectively. 

Figure 14.2. Undermining of nickel electrodeposit on steel by galvanic corrosion in 3% NaCi solution (lOOx). Crack resulted from cyclic stressing in a corrosion-fatigue test [H. Spahn and K. Fassler, Werkst Korros. 17, 321 (1966)].

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