CORROSION OF NICKEL BASED ALLOY G-30 BETWEEN 100 AND 420 deg C, pH VALUES FROM 2 TO 6 AND PRESSURES RANGING FROM 250 TO 480 BAR UNDER CONDITIONS OF SUPERCRITICAL WATER OXIDATION

摘要

Supercritical water oxidation (SCWO) is a promising and very effective method for the oxidation of organic wastes. Its high solubility for organic compounds and its special physical properties (i.e. density, viscosity) resulting in a key advantage over standard processes like incineration. Due to the formation of HCl during oxidation of chlorine organics, a severe corrosion attack of most of the materials has been observed. This paper describes the results of investigations of nickel base alloy G-30, exposed at pH values from 2 to 6, temperatures ranging from 100-420 deg C and pressures between 250 and 480 bar at duration's of 120 hours in a CH_2Cl_2/H_2O_2- respectively NaCl/H_2O_2-mixture with about 2000 wppm of chloride. The weight losses varied between a few and 200 mg/cm~2, depending on the environmental conditions during the tests. The corrosion attack in the subcritical region increased at pH 6 with increasing pressure in the temperature range between 150 and 250 deg C. The maximum of the metal loss was nearly independent of pressure at around 250 deg C. With increasing temperature, especially in the supercritical fluids, a reduced attack was found for high pressures, whereas for 250 bar a strong increase was obvious. At a pH of about 2, the corrosion attack increased with decreasing pressure between 100 and 380 deg C. Above the critical point, a reversed behavior was found i.e., the corrosion attack increased with increasing pressure or density of the fluid.