Nickel erosion-corrosion

The resistance of a metal to erosion-corrosion is based principally on the tenacity of the coating of corrosion products it forms in the environment to which it is exposed. Zinc (brasses), aluminum (aluminum brass), and nickel (cupronickel) alloyed with copper increase the coating s tenacity. An addition of V2 to 1)4% iron to cupronickel can greatly increase its erosion-corrosion resistance for the same reason. Similarly, chromium added to iron-base alloys and molybdenum added to austenitic stainless steels will increase resistance to erosion-corrosion. 

Fig. 1.94 Effect of chromium additions on the erosion corrosion of 70/30 cupro nickel in...

It is possible for the passivation (oxide) layer on the surface of a metal to be continuously removed or not allowed to develop, by erosion from particulate matter or gas bubbles. Not only is the surface eroded but the removal of the protective oxide layer allows corrosion to take place. The problem is accentuated by the presence of an obstruction or debris, on the metal surface that diverts and accelerates the flow near the surface along a defined path. Sato et al [1977] report experimental data on erosion-corrosion resistance of condenser tubes fabricated from various cupro nickel alloys. They suggest that high iron bearing cupro nickels are superior in respect of erosion corrosion by clean sea water. 

This type of behaviour has been observed for the nickel-chromium alloy system. In this work, pure nickel, Ni-20 wt% Cr and Ni-30 wt% Cr alloys were exposed to erosion-corrosion at 700 and 800 °C. An erosive stream, loaded at 400 mg min of 20 iJiva alumina particles and flowing at 75 and 125 m s , was used to impact normally on the specimens. Under simple oxidation in air at these temperatures, the alloys both developed protective scales of chromia and showed very low rates of... 

Copper-nickel alloys are used in tubings and coils of heater and air-conditioning systems because of their high thermal conductivity in heating and cooling applications. Copper-nickel alloys such as 70/30 Cu/Ni and 90/10 Cu/Ni have sufficient erosion-corrosion resistance in water compared to pure copper. 

Syrett BC. Erosion corrosion of copper-nickel alloys in seawater and other aqueous environments - A literature review. Corrosion, 32(6), June 1976. 

Hodgkiess, T. and Vassiliou, G. (2003) Erosion Corrosion of Copper—10% Nickel Alloy Revisited, JCSE, Vol. 6, Paper C038, pp. 1-A. 

Figure 15.4 Mapping electrochemical material loss against mechanical erosion rates for a nonpassivating surface carbon steel (AISI1020) along with two potentially passivating surfaces of nickel aluminum bronze (NAB) one that has been thermally sprayed by high-velocity oxy-fuel deposition as a coating on carbon steel ( j and another which has been cast (A.). These results were obtained from jet impingement erosion-corrosion tests. Reprinted from Ref. [7]. Copyright (2007) with permission from Elsevier.

Copper alloys (Admiralty, copper-nickel) and austenitic stainless steels are the most commonly used materials for feedwater heater tubing based upon their resistance to general and localized corrosion, erosion-corrosion, and SCC, and adequate heat transfer performance [1,2]. Carbon and low-alloy steels are most often used for the shells of such heaters for economy and availability. 

Stainless steel and nickel base alloys are generally resistant to erosion corrosion. Because the vessel internals are made of stainless steel, erosion corrosion resistance of BWR vessel internals has been excellent under design basis operating conditions... 

Stainless steels of all grades, in general, are resistant to erosion corrosion. The addition of nickel, chromium, and molybdenum further improves their performance. Stainless steels and chromium steels are resistant as a result of their tenacious surface films. 

The addition of a minor element can also improve the resistance of copper-nickel alloys to erosion-corrosion. The effect of iron content on the corrosion and impingement resistance of 90/ 10 copper-nickel is maximized with the addition of about 2 percent... 

Aluminum bronzes containing 7% Al, 2% Ni, show an outstanding resistance to de-alloying and cavitation corrosion in most fluids and seawater, because of nickel addition which is highly resistant to corrosion. Aluminum bronze, such as 76 Cu-22 Zn-2 Al, are used for marine heat exchangers and condenser because of its excellent corrosion resistance. Aluminum is responsible for increased corrosion resistance. But the velocity must not exceed a safe threshold to avoid erosion-corrosion. 

Erosion-corrosion It is often observed on the outer radius of pipe bends in oil and gas production due to rather high fluid flow rates as well as corrosive environments where flow exceeds 6 m/s for copper nickel and 10 m/s for carbon steel. 

Copper-based alloys. The copper-based alloys are velocity-limited, as impingement attack occurs when the hydrodynamic effect caused by seawater flow across the surface of such alloys exceeds the value at which protective films are removed and erosion-corrosion occurs. Thus, if these alloys are to exhibit high corrosion resistance, they must be used at design velocities below this limiting value. A more detailed coverage of the marine usage of two important copper-nickel alloys is presented in the section on copper alloys. 

Second, better inherent corrosion resistant can also be used to increase the erosion-corrosion resistance of cast irons. Austenitic nickel cast irons can have hardness similar to unalloyed cast irons but may exhibit better erosion resistance because of the improved inherent resistance of nickel alloyed irons compared to unalloyed irons. 

Nickel increases corrosion resistance by the formation of protective oxide films on the surfaces of the castings. Up to 4% Ni is added in combination with chromium to improve both strength and corrosion resistance in cast iron alloys. The enhanced hardness and corrosion resistance obtained is particularly important for improving the erosion-corrosion resistance of the material. Nickel additions enhance the corrosion resistance of cast irons to reducing acids and alkalies. Nickel additions of 12% or greater are necessary to optimize the corrosion resistance of cast irons. 

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