A study on corrosion mechanism of 15CrMo in saline (Na2SO4) steam at high temperature

To clarify the corrosion mechanism of 15CrMo in saline (Na2SO4) steam, the experiments were conducted on a novel setup. The samples were analyzed by scanning electron microscope and X-ray photoelectron spectroscopy. The results indicate that insoluble sulfide, FexSy, would form on the gas-phase corroded surface while it would not occur on the liquid-phase corroded surface. The salinity of water/steam has a destructive effect on hydrogen bonds. Compared with deionized steam/water, salinity accelerates the corrosion of steel in two ways electric current intensification in primary cell and energy promotion of the solution system. FeOOH does not change obviously with the increase of salt concentration. The relative variation values of FeOOH content with salt concentration are only 2.43% (gas) and 3.40% (liquid), respectively. Besides, the FeOOH content on the liquid-phase corroded surface is much greater than that on the gas-phase corroded surface regardless of the salt concentration. The content of Fe3O4 in the gas/liquid phase decreases from 17.01%/24.58% to 6.02%/18.30%. The Fe2O3 content in the gas/liquid phase increases from 40.12%/9.85% to 73.62%/17.05%.