The current proposed ASTM GT fuel oil specifications for gas turbines imposes certain limits on contaminants. This paper presents some operating experiences with two gas turbines using a fuel oil that approaches these maximum limits for vanadium and sodium for the proposed Nos. 1, 2, and 3 GT fuels. One year’s satisfactory operation was achieved although evidence of minor corrosion was present, but insufficient to cause replacement of components.

Effects of temperature and contaminant levels on the high-temperature corrosion of superalloys used in gas turbines were investigated using pressurized passages which simulate the operating conditions of present-day gas turbines. The alloys were tested in a cooled configuration realistically simulating the air-cooled vanes and blades of a gas turbine. Conclusions are drawn as to the permissible level of contaminants and the effect of metal cooling on high-temperature corrosion. It is shown that the surface temperature of a blade or vane rather than the gas-stream temperature is the critical factor in determining the amount of attack to be expected at a given contaminant level and the amount of attack is an exponential function of this temperature. Furthermore, in a dynamic-type test no decrease in corrosion rate is noted at higher temperatures. It was concluded that the use of a 5 ppm Na/2 ppm V fuel would result in an excessive amount of attack with a metal surface temperature of 1500 deg F.

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Surface analysis of gas-turbine-blade material before and after exposure to the combustion products of residual fuel oils, demonstrates the corrosive effect of these products, and a measurable indication may be obtained in a fraction of the testing time required to produce appreciable weight loss. Surface analysis has the further advantage that it is possible to measure corrosion in specific regions on a specimen where the specimen has been exposed to a gas-flow pattern with a well-defined temperature profile. Weight-loss measurements following long-time tests have shown good agreement with this method of analysis. The fusion temperature of the fuel ash appears to be a reliable criterion for judging the potential corrosivity of residual fuel oil, and good correlation has been obtained between ash-fusion temperatures and corrosion both for untreated oils and oils with additives.

Some of the problems encountered in combustion-system design are discussed with particular attention to combustor discharge-temperature patterns. The results of extensive laboratory and field tests that culminated in improved temperature patterns are presented.