Effect of KCl on high-temperature corrosion of low-alloyed steel under low oxygen partial pressure

Low oxygen environments in biomass gasification and the presence of chlorine in feedstocks can influence the corrosion rate of steel by affecting the formation of protective oxide scales. The effect of KCl on the high-temperature corrosion of low-alloyed steel (13CrMo4-5) under low oxygen partial pressure is investigated by KCl salt spray (0.1 mg·cm⁻²) and exposure to 3 vol% H₂ + 30 vol% H₂O + Ar (balance) at 500°C for up to 168 h. Specimens without KCl salt are exposed for reference. Specimens are characterized after exposure by mass change, SEM/EDS, and XRD. KCl-deposited specimens exhibit about 30% lower mass gain after exposure compared to non-sprayed specimens. Their scale shows a porous innermost layer and a denser layer on top. No Fe or Cr chlorides are identified. The specimens without salt exhibit a similar two-layered scale, with a porous inner Fe-Cr oxide, followed by a denser and thicker Fe-oxide above. KCl could potentially protect the surface from further degradation by physically covering the specimen, altering the scale morphology, and forming a less permeable barrier, hindering the transport of species through the scale.