Effects of Silicon and Titanium on the Corrosion of Low-Alloy Steels in a Simulated Coal Gasification Environment at 600°C

Results of corrosion tests carried out on a series of Fe-12% Cr alloys in coal gasification environments at 600°C were studied. Effects of Si and Ti on corrosion resistance were assessed using data obtained from a commercial 12% Cr alloy, type 410 (UNS S41000), three specially cast “model” 12% Cr alloys containing 2.7% Si with Ti levels of 0%, 0.4% and 0.7%, respectively, and a higher alloy (type 28 [UNS N08028]) heat exchanger steel. Corrosion tests were carried out using a simulated dry-feed entrained slagging gasifier gas. The gas (64% carbon monoxide [CO], 3.8% carbon dioxide [CO₂], 0.8% hydrogen sulfide [H₂S], and balance H₂ [in vol%]) was premixed and passed over the test pieces at a rate high enough to prevent thermodynamic equilibrium achievement. Results showed that Si had a strongly beneficial influence on corrosion resistance. Ti, depending upon the amount added, exerted a positive or negative influence on corrosion resistance and reduced problems associated with workability. The kinetics of corrosion were presented in terms of weight-change and metal-loss measurements, the synergistic influences of Si and Ti were discussed, and corrosion resistance was compared with that exhibited by a commercial 12% Cr steel and type 28, the higher alloy material.