Hot Corrosion Study of 9Cr–1Mo Boiler Steel Exposed to Different Molten Salt Mixtures

The present study is an attempt to observe the hot corrosion behavior of P91 boiler steel when exposed to different molten salt environments at higher temperature. The hot corrosion behavior was observed for temperature range 550–850 °C under the application of air, 40% Na2SO4 + 60% V2O5 (salt 1), 40% K2SO4 + 60% NaCl (salt 2), 50% Na2SO4 + 50% NaCl (salt 3), 40% Na2SO4 + 40% K2SO4 + 10% NaCl + 10% KCl (salt 4). Thermogravimetric study results in parabolic oxidation kinetics when the specimen was exposed to temperature 550 °C and 650 °C, whereas multistage oxidation kinetics was observed at temperatures above 650 °C. An acceleration in the oxidation process was observed with the increase in the exposure temperature, also causing an increase in the oxide scale thickness. Specimen exposed to salt mixtures containing more Na2SO4 and NaCl (salt 2 and salt 3) experienced severe corrosion attack at 750 °C and 850 °C. Thick, non-adherent, and porous magnetite and hematite layers were observed on the outer scale of the specimen which resulted in higher weight gain of the alloy. The corrosion rate of P91 alloy exposed to different salt mixtures was in the order: salt 3 > salt 2 > salt 1 > salt 4 > air.