Browsing by Author "Koster, Max"

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    Comparison of sodium sulphate deposition rate models based on operational factors influencing hot corrosion damage in aero-engines
    (American Society of Mechanical Engineers, 2021-01-11) Pontika, Evangelia; Laskaridis, Panagiotis; Nikolaidis, Theoklis; Koster, Max
    Hot corrosion is defined as the accelerated oxidation/sulphidation in the presence of alkali metal molten salts. It is a form of chemical attack that causes good metal loss. Current lifing models in aircraft engines focus on creep, fatigue and oxidation while hot corrosion damage has been overlooked as being of secondary importance. However, the absence of hot corrosion lifing models for aircraft engines often leads 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 requirement for including hot corrosion in the damage prediction process of aircraft engines. In both theoretical and experimental studies in literature, deposition of molten salts is identified as one of the primary conditions for hot corrosion to occur and an increased amount of deposited liquid salts accelerates the attack. Currently, most hot corrosion studies are limited to experimental testing of superalloys which are pre-coated with a controlled layer of salts. Such experimental studies are disconnected from gas turbine operating conditions during service. The present paper analyses two deposition rate models applicable to gas turbine operating conditions using Design of Experiments. Design space exploration is presented by taking into account gas turbine operating parameters which vary during a flight as well as temperature ranges where hot corrosion can occur. Analysis of variance is presented for 6 input parameters using Box-Behnken 3-level factorial design. Results from the Analysis of Variance indicate that the deposition rate models are sensitive to pressure and salt concentration in the gas flow. Finally, the saturation point of sodium sulphate has been investigated within the operating range of gas turbine and it was found that it can vary significantly under different conditions.
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    Hot corrosion damage modeling in aeroengines based on performance and flight mission
    (AIAA, 2024-10) Pontika, Evangelia; Laskaridis, Panagiotis; Nikolaidis, Theoklis; Koster, Max
    Hot corrosion is a form of chemical damage that causes surface degradation, sound material loss, and reduced component life. A lifing analysis in aeroengines without considering hot corrosion can lead to unexpected damage findings and increased scrap rates due to blade thickness loss beyond repair. This paper presents a novel methodology to predict hot corrosion damage based on aeroengine performance and flight mission analysis while taking into account environmental exposure, fuel quality, and material factors. The participating mechanisms, from salt and sulfur ingestion to deposition and hot corrosion attack, are discussed to explain the phenomenon in aeroengine components. In the investigated engine type, the first stage of the low-pressure turbine is the most affected. The application of the new methodology provides insights into the damage progression during the flight, the most affected components and the importance of capturing variations in the fuel quality, environmental exposure at the flight region, and the thrust derate policy. For a representative 1500 n mile mission, the variations in environmental exposure, fuel quality, and derate policy within typical limits can result in up to +350% damage. The outputs of the new framework can inform the decision making for maintenance, repair, and overhaul contract costing and scheduling.
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    ItemOpen Access
    Hot corrosion damage modelling in aero engines based on performance and flight mission analysis
    (AIAA, 2023-01-19) Pontika, Evangelia; Laskaridis, Panagiotis; Nikolaidis, Theoklis; Koster, Max
    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.