The effectiveness of aluminum thermal spray coating in the corrosion resistance of an ASTM A 387 G11 low alloy steel was evaluated under two conditions: an oxidant atmosphere in a fluid catalytic cracking regenerator of a petrochemical unit and a simulating atmosphere in the laboratory, in the temperatures of 650 degreesC and 700 degreesC. To provide a reference for the behavior of the uncoated substrate, samples of G11 steel without coating were also studied on both conditions, real and simulated. The characterization of the phases present in the oxidized layer was carried out by x-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM) with X-ray energy dispersive analysis (EDS). The aluminum coated G11 steel, in both real and simulated conditions, presented a complex inner layer containing Fe-Al intermetallic phases and iron rich oxides and sulfides. Internal oxidation and sulfidation were also observed. In the G11 uncoated steel, a severe corrosion was observed in both, real and simulated conditions, with formation of several iron oxides (Fe2O3, Fe3O4 and FeO). Internal oxidation and sulfidation of chromium in the alloy were also observed.