Effect of gas flow rate on oxidation behaviour of alloy 625 in wet air in the temperature range 900–1000 °C

Abstract

In many industrial processes, the flow rate of hot gaseous service environments may be in the range of several m/s. In the present paper, the effect of gas flow rate on the high temperature oxidation behaviour of alloy 625 in wet air is presented. The gas velocity was varied from near static conditions to linear gas flow rates up to 6 m/s. The oxidation kinetics were studied by gravimetry during cyclic/discontinuous testing at 900 and 1000 °C. The oxide scales and the subsurface depletion zones formed during exposure were studied by light optical microscopy, scanning electron microscopy with energy dispersive X‐ray analysis and, for selected specimens, by electron backscatter diffraction. It was found that Cr loss due to formation of volatile species is substantially enhanced by high gas flow rates thus significantly influencing the oxidation limited life time of the oxidising component. Within the studied range of flow rates no plateau value was reached, the Cr loss being substantially larger at a flow of 6 m/s than at 0.7 m/s. Additionally, it was found that geometrical factors of the test specimen substantially affected the extent of volatile species formation. Especially the leading edge of the specimen exhibited more extensive Cr loss than the other specimen areas.

Volatilization kinetics of chromium oxide, manganese oxide, and manganese chromium spinel at high temperatures in environments containing water vapor

“…Similar results were received from Pint and Young who observed a proper accordance of calculated and experimental data at low flow rates of approximately 17 mm/s using Equation . This is in marked contrast to Huczkowski et al, in which they argue that Equation is not applicable for low flow rates due to the interference of the boundary layers.…”

“…The derivation of the formula is accurately described . Huczkowski et al demonstrated the limitations of Equation . Especially the width of the boundary layer along the specimen is frequently similar to the diameter of the reaction tube at low flow rates.…”

A comparison of the high-temperature oxidation behaviour of conventional wrought and laser beam melted Inconel 625

“…While many investigations [15][16][17][18] have been carried out on the oxidation behaviour of conventional Inconel 625 in air, there has been less work on the high-temperature reactivity of the 3D manufactured Inconel 625 [19].…”

Effect of pressure and impurities on oxidation in supercritical CO2

“…At high pressure, O 2 additions have shown slightly negative effects or little effect . It has been suggested that combinations of H 2 O and O 2 at high pressure could react with Cr‐rich reaction products to form volatile Cr oxy‐hydroxides thereby accelerating the degradation rate (ie, rate of Cr loss) of both Fe‐ and Ni‐base alloys . This degradation would be particularly important for thin‐walled structures in heat exchangers.…”