NaOH-induced corrosion in thermal convection loops made of Ni 201 and Inconel 600

This study explored molten NaOH-induced polythermal corrosion behavior of Ni 201 and Inconel 600 through comparative analysis of thermal convection flow loops after 1000 hours. In the free-convection loops, the circulation of molten NaOH was facilitated by an 85°C temperature gradient between hot (460°C) and cold legs (375°C). Post- analysis of samples collected from the hottest and coldest points were made by X-ray diffraction, scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. Additionally, static corrosion tests of Ni 201 and Inconel 600 rods were conducted at 460°C for comparison between isothermal and polythermal corrosion to investigate the effect of flow. Results reveal differing corrosion behaviors, with Ni 201 exhibiting deeper corrosion attack compared to Inconel 600 in the flow loops, while Inconel 600 showed thicker oxides scales after static exposure compared to Ni 201. Microstructural analysis indicates mass transfer and intergranular attack in the flow loop of Ni 201 and selective leaching and oxidation of the least noble elements of the Inconel 600 flow loop.