Nickel alloys are a common material used when typical steel materials don’t offer the corrosion performance that is needed. Hastelloy offers in general a better corrosion performance than
titanium. Only a few metals like e.g.
Zirconium and
Tantalum is supperior to
Hastelloy concerning the corrosion resistance in demanding media like
hydrochloric acid and
sulfuric acid.
Focusing on some of the more
corrosion resistant nickel alloys, C-22, C-276 and B-2 all have good corrosion resistance in a variety of media. In the case of
HCl, the corrosion resistance of these alloys depends greatly on the molybdenum content. The alloy with the highest concentration of molybdenum, B-2, exhibits the best
corrosion resistance.
When dealing with aqueous solutions to enhance the performance of nickel materials, the most important alloying elements are Fe, Cu, Si, Cr and Mo with Cr and Mo playing a major role in nickel
corrosion resistance. By varying the concentrations of Cr and Mo in the
nickel alloys the corrosive environments in which nickel alloys can be successfully applied are varied, but they typically are found in a range of acid, salt and alkali applications. The additions of chromium (15% -30%) improves the
corrosion resistance to oxidizing solutions while the addition of molybdenum (up to 28%) significantly improves the resistance to nonoxidizing acids.
Approximate Alloy Concentrations |
|
Cr |
Mo |
|
22% |
13% |
|
16% |
16% |
|
1% |
28% |
In other solutions such as
nitric acid (HNO3) chromium is an essential alloying element responsible for providing the corrosion resistance in this environment. Nickel alloys weaknesses evolve around it interaction with the media and its environment in the form of impurities. Under ideal testing conditions, for example B-2 alloy works well in pure de-aerated
H2SO4 and HCl but deteriorates rapidly when oxidizing impurities, such as oxygen and ferric ions are present. Another important consideration is the presence of chlorides (Cl-). Chlorides generally accelerate the corrosion attack, but the degree of acceleration differs for various alloys.
