Hot corrosion damage modelling in aero engines based on performance and flight mission analysis

Lifing models for aircraft engines are mainly focused on creep, fatigue and oxidation, while hot corrosion remains one of the least explored areas. Hot corrosion is a form of chemical damage that causes surface degradation, sound material loss and reduced component life. A lifing analysis for aircraft engines without considering hot corrosion can lead to unexpected and unexplained hot corrosion findings by aircraft engine operators and Maintenance, Repair and Overhaul (MRO) providers during inspections. Although hot corrosion does not cause failure on its own, the interaction with other damage mechanisms can reduce component life significantly. Consequently, there is a necessity for including hot corrosion in the damage prediction process of aircraft engines. This paper presents a new methodology to estimate hot corrosion damage based on aero-engine performance and flight mission analysis while taking into account environmental exposure, fuel quality and material factors. The analysis in the present paper focuses on the hot corrosion progress over the course of the flight mission, while varying the major contamination factors and thrust derate, and the hot corrosion rate over flight time is then used to calculate the damage at the end of the mission. The participating mechanisms, from salt and sulfur impurity ingestion to deposition rate and hot corrosion attack, are analytically presented to explain the progress of the phenomenon in aero-engine components. In the investigated type of engine, the first stage of the low-pressure turbine is found to be the most affected. It is concluded that hot corrosion is favored by a combination of high pressure, high sulfur oxide concentration, and high salt deposition rate within an intermediate temperature range while the gas conditions near the component surface remain below the sodium sulfate saturation point, and these conditions are linked with aero-engine operation. The presented hot corrosion framework captures the effect of mission requirements, component operating conditions, environmental exposure, fuel quality and material on the hot corrosion damage of hot section components. It can be used to inform aero-engine maintenance planning, lifecycle analysis and MRO contract-costing, and can benefit digital twins for predictive maintenance.