Laboratory Procedures for Evaluating High-Temperature Corrosion Resistance of Gas Turbine Alloys

With an increasing interest in the burning of heavy fuels in gas turbines there is also concern with the precise determination of the corrosive effects which may arise from the use of these fuels. Of particular interest is a class of fuels known as ASTM Specification No. 3-GT which has a low level of metal contaminant, nominally up to 5 ppm alkali metal and 2 ppm vanadium. In this paper we describe experimental laboratory equipment and the program with which we determine the extent of corrosion to be expected when such fuels are burned in gas turbines. The results using several pieces of experimental apparatus are presented, and their correlation with available field experience is considered. In general, the amount of deposit which collects on the blade surface and precedes corrosive attack is proportional to the amount of contaminant in the gas stream. There is a significant influence of stream velocity and/or pressure on hot corrosion which must be considered in applying the results from low-velocity low-pressure rigs to operating gas turbines. According to the data obtained in a pressurized passage which realistically simulates the actual gas turbine, fuel containing 5 ppm Na and 2 ppm V is too corrosive to use in the gas turbine at a 1500 deg F metal temperature.