Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NO x Environments

Abstract

Due to their excellent corrosion resistance, iron aluminum alloys are currently being considered for use as weld claddings in fossil fuel fired power plants. The susceptibility to hydrogen cracking of these alloys at higher aluminum concentrations has led researchers to examine the effect of chromium additions on the corrosion resistance of lower aluminum alloys. In this work, three iron aluminum alloys were exposed to simulated coal combustion environments at 500 and 700°C for short (100 h) and long (5000 h) isothermal durations. Scanning electron microscopy was used to analyze the corrosion products. All alloys exhibited excellent corrosion resistance during short term exposures. For longer test times, increasing the aluminum concentration improved alloy corrosion resistance. The addition of chromium to the binary iron aluminum alloy prevented the formation iron sulfide and resulted in slower corrosion kinetics. A general classification of the scales developed on these alloys is presented.

Laboratory corrosion testing of coatings and substrates simulating coal combustion under a low NOx burner atmosphere

“…. In heavily sulfidizing atmospheres where H 2 S is present, large amounts of iron based sulfide nodules are observed . In the present tests, H 2 S was not included in the gas mixture, but it must have likely formed due to the presence of S in the ash, under the low NO x atmosphere.…”

“…For instance, slurry aluminides have been exposed to steam for over 22,000 h in the bypass of a steam turbine at 640 °C and 180 bar without substrate degradation and under laboratory testing conditions (100% steam, 650 °C, 1 bar) the same coatings have reached 50,000 h of exposure (the test is still ongoing) . DuPont et al have also demonstrated that FeCrAl containing alloys exhibit an outstanding corrosion resistance in sulfidizing and oxidizing conditions due to the formation of a protective Al 2 O 3 scale stabilized by the presence of Cr .…”

“…Moreover, FeCrAl alloys are currently under study due to their low cost and excellent corrosion resistance. However there are still weldability issues that need to be addressed .…”