EFFECT OF SULFUR IN JP-5 FUEL ON HOT CORROSION OF COATED SUPERALLOYS IN MARINE ENVIRONMENT
2006
Quigg, H. T. | Schirmer, R. M.
An experimental investigation was made to determine whether the 0.4 per cent by weight of sulfur allowed in JP-5 fuel is a safe level for the protection of coated superalloys, used in aircraft-turbine engines of advanced design, when operated in a marine environment. Environment was simulated in the turbine section of an aircraft engine with respect to temperature, velocity, pressure, and stoichiometry. Tests were conducted with a nickel-base alloy (Inconel 713C) uncoated, with an aluminum-diffusion coating (Misco MDC-1), and with an aluminum-chromium-diffusion coating (Misco MDC-9) at all combinations of three levels of sulfur in fuel (<0.0040, 0.040, and 0.40 weight per cent) with two levels of sea salt in air (zero and 1.0 ppm). Exponential equations of weight-loss with time were developed, and statistically-significant effects were identified at a 95 per cent confidence level. In all comparisons, the removal of sea salt from the air significantly decreased the relative rate of corrosion; thus, indicating sea salt to be a primary-causative agent of hot corrosion. The effect of sulfur in fuel varied with the superalloy coating and the absence or presence of sea salt. In the absence of sea salt in air, a reduction of sulfur in fuel from the present limit to either 0.040 or <0.0040 weight per cent decreased attack with one coated superalloy and increased attack with the other. In the presence of 1.0 ppm sea salt in air, a reduction in sulfur to 0.040 weight per cent had no significant effect on attack; however, a reduction to <0. 0040 weight per cent significantly decreased the relative rate of attack with both coated superalloys.
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