Chemical-looping combustion (CLC) holds significant potential for improving steam data when using renewable fuel for heat and power production. This is achieved by positioning superheater tubes in the air reactor (AR) side, where a mild corrosive environment is anticipated. However, alkali-containing ash may be transported from the fuel reactor (FR) to the AR via the bed material, leading to the release of volatile alkali compounds such as KOH(g) that may influence the corrosion rate of the superheater tubes. In this study, we examine potential corrosion challenges of superheaters positioned in the AR of a CLC unit when utilizing renewable fuel. This was achieved by developing an experimental set-up to study the influence of KOH(g) on the corrosion rate of materials relevant to superheater application. The materials were exposed at 700 °C in a 5% O2 + 3% H2O + N2 + 20 ppm KOH(g) environment for 168 hours and the corrosion rate was compared with an environment absent of KOH(g). Cross-sections of the exposed samples were carefully prepared using ion beam-milling and were analyzed with SEM/EDX and XRD. We show that KOH(g) plays a pivotal role by rapidly destroying the primary protective Cr-rich oxide scale on stainless steels and Ni-base alloys, resulting in the formation of a multilayer oxide scale with inferior protective properties (the so-called secondary protective oxide). On the contrary, the FeCrAl alloy tested retained a primary protective Al-rich oxide scale after exposure to KOH(g) with a similar corrosion rate as for the sample exposed without KOH(g).