Effects of Sulfides on the Corrosion Behavior of Inconel 600 and Incoloy 825 in Supercritical Water

Abstract

Corrosion tests of Inconel 600 and Incoloy 825 were performed in supercritical water containing sulfides at 520°C and 25 MPa. The scales formed on Inconel 600 consisted of a thick outer layer of almost pure Ni 3 S 2 and an inner layer predominantly of Cr-rich spinels with a Ni 3 S 2 network inside. The scales of Incoloy 825 also had a multilayered structure. The outer layer primarily consisted of Ni 3 S 2 and (Ni,Fe) 3 S 4, followed by a thicker intermediate mixture layer of chromium-rich oxides, Ni 3 S 2, and (Ni,Fe) 3 S 4 , an inner layer of predominantly Cr 2 O 3 and a small amount of Ni 3 S 2 toward the substrate. Incoloy 825 showed slightly better corrosion resistance than Inconel 600 due to its higher Cr content. By means of superimposed isothermal phase diagrams and evaluation for the partial pressures of oxygen and sulfur in the designated atmosphere, the corresponding corrosion mechanisms were discussed, based on the present investigation.

Modelling and Analysis of the Corrosion Characteristics of Ferritic-Martensitic Steels in Supercritical Water

“…Taking magnetite as an example, which has been studied extensively as a function of oxygen partial pressure, the critical boundary oxygen partial pressure (pc,o2) is ~10 −6 atm at 1200 °C [48], ~10 −8.3 atm at 1000 °C [46], ~10 −20 atm at 600 °C [11], ~10 −25 –10 −22 atm at 500 °C [11,46], and ~10 −30 atm at 400 °C [11]. Previous studies have suggested that the rate-controlling step in the corrosion of ferritic-martensitic steels in SCW is the outward diffusion of iron and that the inner layer generally plays the role of the protective barrier layer [7,8,10,12,30,33,51]. However, the inner layer grows into the metal phase at the metal/inner layer interface [52,53], and the cations diffusing outwards through the inner layer are not involved in the growth of the inner layer into the metal.…”

Supercritical Water Oxidation for Environmentally Friendly Treatment of Organic Wastes

“…[21][22][23][24][25]. A series of investigations on the corrosion resistances of these materials under supercritical and/or subcritical conditions [20,24,[26][27][28][29][30], reflected that no one kind of material can withstand corrosion at all conditions, but some exhibit perfect corrosion resistance under specific conditions, as given in Table 1. Thus, appropriate reaction conditions such as heteroatom types in feedstock, reaction temperature, and pressure should be optimized in order to minimize corrosion rate for a chosen reactor construction material.…”

“…The dissolved metal cations combine with anions such as OH − in aqueous environments to form oxides or hydroxides; they then precipitate on specimens surface to form and/or thicken the outer layer [49]. Li et al [30] reported that the corrosion of Inconel 600 and Incoloy 825 in low density SCW containing sulfides also follows the solid-growth mechanism.…”

Early oxidation of Super304H stainless steel and its scales stability in supercritical water environments

“…According to the expected temperature and pressure, a predetermined volume of deoxygenated water was loaded in the autoclave. The detailed information about experimental apparatus and procedures can be obtained from our previous studies [12,13]. In order to explore the effects of operation parameters, such as temperatures, pressures, and initial pH value of experimental water, on the initial oxidation state of Super304H in supercritical water, tests with an exposure time of 40 h under various conditions were carried out.…”