Aspects of the Corrosion Kinetics for Binary Nickel-Chromium Alloys under Conditions Found in Supercritical Water Oxidation Plants Processing Chlorinated Substances

Abstract

Binary Ni-Cr alloys (0 to 45 mass% Cr) were exposed to an aqueous solution resulting from the oxidation of dichloromethane (CH 2 Cl 2 ) in the presence of hydrogen peroxide (H 2 O 2 ) at 40 MPa and temperatures between ~100°C and 415°C. The composition of the reaction medium after complete oxidation of the chlorinated hydrocarbon was 0.12 m hydrochloric acid (HCl), 0.06 m oxygen (O 2 ), and 0.06 m carbon dioxide (CO 2 ). Of the alloys investigated, NiCr25 performed best in experiments for 120 h under these conditions. Aspects of the complex corrosion kinetics for binary Ni-Cr alloys are compared with the predictions of a mathematical model. Results from other investigations that cover temperatures up to 500°C at a comparable pressure are reviewed in light of the new fi ndings.

Corrosion Characteristics of Typical Ni–Cr Alloys and Ni–Cr–Mo Alloys in Supercritical Water: A Review

“…Inconel 690 has excellent corrosion resistance among the commonly used Ni–Cr alloys, because it has a higher Cr content (27–31 wt %) than the other Ni–Cr alloys, including Inconel 600, Inconel 601, and Inconel X-750 (recall Table ), This is the reason why Inconel 690 becomes the representative grade of Ni–Cr corrosion-resistant alloys and is the focus of experimental studies. Notably, NiCr25 performs best in the CH 2 Cl 2 solution at 100–415 °C and 40 MPa, other than NiCr45, with the highest Cr content among NiCr0, NiCr25, NiCr30, NiCr35, and NiCr45 . Accordingly, the influence of the Cr content on the corrosion resistance and corrosion rate of alloys with a Cr content of >30 wt % in SCW requires further discussion.…”

“…Despite having a high price, niobium exhibits the optimum corrosion resistance in SCW at 380−390 °C and 25 MPa among Inconel 625, SS 316L, Ni-20Cr, and niobium. 45 Schroer et al 46 found that NiO inhibited the dissolution of Ni-containing oxide layers, thereby effectively protecting metal from further corrosion. The corrosion behaviors of binary Ni−Cr alloys with different Cr contents in SCW indicate that the Ni−Cr alloys have the best corrosion resistance when the Cr content is ∼25 wt %.…”

“…A recent study shows that removing intergranular carbides using a prior solution-annealed treatment can decrease the crack growth rates by a factor of 4 in subcritical water at 360 °C. 48 Table 3 summarizes the experimental conditions and principal findings related to the corrosion of Ni−Cr corrosion-resistant alloys in subcritical and supercritical 46 Accordingly, the influence of the Cr content on the corrosion resistance and corrosion rate of alloys with a Cr content of >30 wt % in SCW requires further discussion. It can be inferred from Table 3 that the alloy grain size is a decisive factor in corrosion mechanism, because oxygen can diffuse into the metal matrix through grain boundaries to internally oxidize the metal.…”

Current and future corrosion challenges for a reliable and sustainable development of the chemical, refinery, and petrochemical industries

“…Under the extreme conditions required, trace amounts of halogens and acids lead to extensive corrosion of many reactor materials. Extensive research efforts are managed on nickel and nickel–chromium alloys in order to overcome this technological lock 1–3. Also new concepts have been developed such as transpiring wall reactors or hydrothermal burners in which, for both of them, the corrosive species are encapsulated in a stream of pure noncorrosive water 4.…”