Effect of alkali chlorides on erosion-corrosion of cooled mild steel and Cr3C2-NiCr coating

A series of erosion-corrosion (E-C) tests was carried out on cooled 1018 steel and HVOF 75Cr(3)C(2)-25NiCr coating using a nozzle-type elevated temperature erosion tester. Several mechanical mixtures of SiO2 (quartz) and NaCl or KCI particles were used as erodent particles. The specimens were water-cooled on the backside. Test conditions attempted to simulate the erosion conditions at the tubes in the convection pass of circulating fluidized bed combustor (CFBC) boilers. The effect of Cl, Na, and K-bearing compounds on the E-C wastage and mechanism were investigated. It was found that the E-C wastage of 1018 steel and Cr3C2-NiCr coating specimens increased with increasing amounts of NaCl and KCI doped in the quartz. The accelerating effect of doping alkali chlorides increased with increasing metal surface temperature and/or environment temperature. The cooled specimens had greater material wastage than those of isothermal specimens and addition of alkali chlorides enhanced this increase. In this investigation HVOF Cr3C2-NiCr coating exhibited even higher E-C wastage than that of 1018 steel.