Comparative study on the high-temperature corrosion mechanisms of boiler steel 15CrMoG induced by Cl2 and HCl in high-chlorine coal combustion environments

Sha’erhu high-chlorine coal from Xinjiang contains more than 1% chlorine. Combustion of this coal releases chlorine-containing flue gas, which severely corrodes boiler waterwalls and threatens safe operation. During the corrosion, part of the HCl is converted to Cl 2 , however, the independent corrosive effect of Cl 2 remains poorly understood. To clarify the differences between Cl 2 and HCl, this study investigated the high-temperature corrosion behavior of 15CrMoG steel in O 2 -free and O 2 -containing atmospheres with HCl or Cl 2 at equal molar Cl concentrations. Mass loss measurement, SEM-EDS, XRD, XPS, and thermodynamic analysis were used. A pronounced acceleration in the chlorine corrosion of 15CrMoG steel was observed between 550 and 650 °C. At 650 °C, the mass losses under HCl and Cl 2 atmospheres surged by 189.55% and 164.41%, respectively, compared with those at 550 °C. Cl 2 , with stronger oxidizing power, preferentially forms the highly volatile FeCl 3 , making it more corrosive than HCl, which mainly yields FeCl 2 . The formation of FeCl 2 , FeCl 3 , and CrCl 3 was directly confirmed by XPS. Combined XRD and EDS results demonstrated that Cl 2 depleted Cr and Mo more thoroughly than HCl. O 2 exhibited a synergistic effect on mass loss in both HCl and Cl 2 environments. O 2 played a dual role: it promoted oxide scale formation and drove a continuous chlorine cycle by oxidizing HCl to Cl 2 and regenerating Cl 2 from volatile chlorides, loosening the corrosion scale and intensifying spallation. This study clarifies the corrosive role of Cl 2 in high-chlorine coal combustion and offers a theoretical basis for anti-corrosion design of waterwalls in such boilers.