Incoloy high-temperature corrosion

Although nickel alloys on the whole offer a better resistance to stress corrosion cracking over the steels, their application in high temperature chloride or alkaline environment and hydrogen sulfide environment may put them to the risk of stress corrosion cracking. Cases of SCC have been observed in high temperature pressurized water in steam generating turbines. Incoloy 800... 

Alloy 800 series are derived from Incoloy 800, originally developed in the 1950s by the International Nickel Company [18]. AUoy 800 series have high nickel and chromium contents which give them superior resistance to corrosion in many kinds of environments (Table 17.2). Titanium and aluminum additions lead to the precipitation of different carbonitrides which enhance the material properties. But this Ti + A1 content also leads to the precipitation of hard y Ni3(Ti,Al) phase which enhances creep resistance but decreases the material ductility at high temperature. This is why the Ti + A1 content has been limited in some specifications (800 HT, 800 SPH). On the other hand, annealed material was historically differentiated from solution annealed material, with the terms grade 1 annealed at approximately 980°C, and grade 2 solution annealed at approximately 1150°C [19]. 

It is important to know whether or not the alloy is resistant to crevice corrosion. For instance, work on the various grades of steels, such as SS 304, carpenter alloy, Incoloy (Alloy 825), Hastelloy (Alloy g), and Inconel (625) showed that the later two alloys were highly resistant to crevice corrosion in ambient and elevated temperature seawater [6]. The alloying elements in various grade of steel affect both the electrochemical and chemical processes, such as hydrolysis, passive film formation, passive current density and metal dissolution. Hence, the effect of major alloying elements, such as Fe, Cr, Ni and Mo and... 

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