Hot corrosion is typically defined as the accelerated high temperature oxidation caused by a thin fused salt deposit in contact with the surface of a metallic material. When alloys used in air and land-base gas turbines experience hot corrosion, Na2SO4 is usually the dominant salt found in the deposit due to the thermodynamic stability of this compound in the presence of sodium and sulfur in an oxidizing gas. In an effort to study the hot corrosion of several Fe- and Ni-base commercial wrought alloys in a gas turbine environment, a burner rig test program was executed. The study was conducted at 900°C (1650°F) and incorporated various test durations and two fuel sultlw contents (0.4 and 1.0 wt%). Also, a synthetic sea salt was injected into the combustion zone of the burner rig, thereby maintaining a specific concentration of the salt in the combustion gas. Tests with the injection of Oparts per million (ppm), 5 ppm, or 50 ppm salt were conducted. The principal constituents of the solution were NaCl, MgC12,Na2SO4, CaCl2, and KCl. In general, the Ni-base alloys tested exhibited superior hot corrosion resistance over the Fe-base alloys. When exposed to a 1000 hour test with the injection of 50 ppm salt, the Fe content of a Ni-22Cr- 18Fe-9Mo alloy appeared to be
detrimental to the hot corrosion resistance of this alloy when
comparedtoaNi-21 Cr-9Mo alloy. The W content in a Ni-22Cr- 14W alloy did not show a detrimental affect on the hot corrosion resistance of this material. Also, Fe-base alloys containing less than 25wt% Cr did not perform well in a 500 hour test burning fiel containing 1.0wt% sulfur and 50 ppm salt injected into the combustion zone. Reasons for the performance of the alloys are suggested to be the “quality” or
protectiveness of the oxide scale grown on a given alloy, the composition of the oxide scale grown on a given alloy -- making the scale more or less susceptible to a synergistic hot corrosion attack, and/or the alloy composition in relation to its ability to resist attack by chloride salts.
Keywords: hot corrosion, burner rig test, commercial alloys, Fe-base alloys, Ni-base alloys