Browsing by Author "Potter, Andrew"
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Item Open Access Assessing the impact of cost optimization based on infrastructure modelling on CO2 emissions(Elsevier Science B.V., Amsterdam., 2010-05-01T00:00:00Z) Harris, Irina; Naim, Mohamed; Palmer, Andrew; Potter, Andrew; Mumford, ChristineTraditionally, logistics design is driven by a need to reduce costs and improve customer service. Recently, the environmental concerns from transport have been increasingly discussed. The traffic levels and associated energy consumption are influenced by supply chain structure, modal split and vehicle utilization. This paper aims to assess the impact of the traditional costoptimization approach to strategic modelling on overall logistics costs and CO2emissions by taking into account the supply chain structure (number of depots) and different freight vehicle utilization ratios (90%, 75% and 60%). The simulation model, based on a European case study from the automotive industry, considers strategic and operational level decisions simultaneously. The analysis shows that the optimum design based on costs does not necessary equate to an optimum solution for CO2emissions, therefore there is a need to address economical and environmental objectives explicitly as part of the logistics design.Item Open Access Corrosion of potential first stage blade materials in simulated supercritical CO2(Taylor and Francis, 2023-05-04) Norman, Boma Phoebe; Al Baroudi, Hisham; Potter, Andrew; Mori, Stefano; Simms, Nigel; Kulkarni, Anand; Sumner, JoyGlobal power consumption is predicted to double by 2050, notably driven by the transportation and energy sectors necessitating limitations of emissions. Due to its compact turbomachinery, better thermal efficiency, and simpler layout, supercritical-CO2 cycles have received attention, with numerous variations proposed (either indirect-fired/closed cycles or direct-fired-open cycles). One technical challenge is degradation pathway quantification of turbine materials in sCO2 as selection is crucial to successfully and economically operate new plants. This requires degradation assessment in representative environments simulating the Allam cycle. Laboratory tests were conducted on a first stage turbine blade alloy, CM247, with either an environmentally resistant coating or bond coat/thermal barrier coat at one atmosphere and 800°C, with potential exposure including (O2, H2O, N2, SO2) for up to 1000 h. Weight change and metallographic measurements tracked scale development. Scanning electron microscopy/energy dispersive X-ray spectroscopy studied scales and internal precipitates. Locations of contaminant element in the CO2-rich environment were investigated.Item Open Access The effects of water vapour on the hot corrosion of gas turbine blade materials at 700 °C(Taylor & Francis, 2022-03-28) Potter, Andrew; Sumner, Joy; Simms, NigelFuture developments in power generation are likely to require gas turbines to operate in novel combustion environments. The level of water vapour in the turbine’s gas stream is one variable that may change as a consequence. This paper explores the effects of water vapour on hot corrosion. The ‘deposit recoat’ technique was used to evaluate the hot corrosion performance of superalloys PWA 1483 and MarM 509 in atmospheres containing between 0 and 20 vol.% water vapour. Exposures were carried out at 700 °C in atmospheres containing 300 ppm SO2 for up to 500 hours. The deposit was an 80% Na2SO4, 20% K2SO4 solution applied with a deposition flux of 1.5 µg/cm2/h. The findings are compared to similar exposures with 3.6 ppm SO2. Increasing levels of water vapour were observed to reduce sound metal loss in atmospheres containing 300 ppm SO2 while increasing sound metal loss in atmospheres containing 3.6 ppm SO2.Item Open Access Further investigations into alloy induced acidic fluxing(Taylor and Francis, 2023-06-04) Potter, Andrew; Sumner, Joy; Simms, NigelGas turbine materials often feature precipitates containing refractory metals to enhance their mechanical strength. This can make them susceptible to alloy-induced acidic fluxing whereby refractory elements increase the acidity of salt deposits. It is not clear to what degree degradation around alloy precipitates is caused by alloy-induced hot corrosion mechanisms, or the inability to develop a protective scale where precipitates are located. The effect of alloy-induced hot corrosion was isolated from the disruption of the protective-scale formation by adding particles of molybdenum to the 80/20 (Na/K)2SO4 deposit for a ‘deposit re-coat’ style hot corrosion test. The resulting morphologies were compared to samples exposed without the addition of molybdenum. Morphology changes were investigated using scanning electron microscopy with energy-dispersive X-ray mapping. Results show a mix of sulphidation and pitting. The effects of molybdenum additions appear more severe for MarM 509 compared to PWA 1483.Item Open Access Hot corrosion in industrial gas turbines.(Cranfield University, 2019-02) Potter, Andrew; Simms, Nigel J.; Sumner, JoyFuture gas fired power stations are likely to use gas turbines operating both at higher temperatures to improve thermal efficiency, and fire cheaper fuels containing more deleterious contaminants. Additional changes relate to potential new methods of CO₂ reduction including pre-combustion capture. These developments in industrial gas turbine technologies present new materials challenges that must be understood. This research aims to further scientific understanding of type II hot corrosion and its effect on a range of candidate alloys for use in industrial gas turbines under novel exposure conditions. Selected parameters have been isolated under those conditions and their effects investigated. Laboratory-based hot corrosion tests using the “deposit recoat” technique were used to evaluate the following variables on candidate materials (GTD 111, Rene 80, PWA 1483, MarM 509, RT22 and SC2464): exposure atmospheres including SO₂ (3.6 to 300 ppm) and water vapour content (0 to 20 vol.%); deposit flux (1.5 and 5 µg/cm²/h of 80% Na₂SO₄ 20% K₂SO₄ ); and the addition of molybdenum particles to deposits. Qualitative assessment of hot corrosion morphologies used a scanning electron microscope (SEM) equipped with energy dispersive X-ray (EDX) spectroscopy capabilities. The effect of water vapour was found to be dependent on SO₂ concentration. Increasing water content increased hot corrosion in low (3.6 ppm) SO₂ atmospheres, but was found to reduce it at higher (300 ppm) SO₂ concentrations. Mixed mode corrosion features have been identified by SEM/EDX analysis, on all samples that progressed from hot corrosion incubation to propagation. These features are attributed to changes in the deposit melt’s chemistry allowing for both acidic and basic fluxing to occur. Refractory metal carbide precipitates were found to exacerbate degradation and acted as nucleation points for hot corrosion damage. It is proposed that this is, at least in part, alloy induced acidic fluxing occurring concurrently with gas phase induced hot corrosion.Item Open Access The hot corrosion of nickel-base disc alloys(Cranfield University, 2011-11) Potter, Andrew; Simms, Nigel J.; Encinas-Oropesa, AdrianaThe efficiency of a jet’s engines has a direct affect on its economic and environmental impact through the quantity of aviation fuel consumed and CO2 emitted. These factors are becoming increasingly important due to higher fuel costs and a greater global awareness of environmental issues. To date, most of the corrosion research work concerning jet turbines has focused on the hottest parts, the turbine blades vanes and combustion chamber. However, as the engines run hotter and with more stress, new superalloys have also been developed for the turbine disc. Although extensive research has been carried out with regard to the mechanical properties of these alloys, relatively little research has been done into their corrosion resistance. The aim of this research is to investigate the hot corrosion characteristics of both the existing and more recently developed disc alloys. Based on these data, the corrosion performance of these alloys was modelled and compared. These aims have been achieved using data from a series of “deposit recoat” corrosion tests on the relevant alloys carried out at Cranfield during the last 6 years. The alloys that are the focus of this study are: Waspaloy, Inconel 718, U720, and RR1000. RR1000 is of particular interest since it is the most recently developed alloy and relatively little is known about its corrosion properties. The tests have been carried over a range of temperatures relevant to the current operating temperatures and the desired higher operating temperatures of the turbine discs. The effects of deposition flux, deposit composition and exposure time have also been investigated as part of this study. A quantitative assessment of the corrosion damage has been carried out and provided metal loss data which has been used to generate empirical models and to compare the effects of variables. The data generated suggest that in the propagation stage of hot corrosion the rate of corrosion is approximately the same between alloys. Therefore the important factor when modelling a disc alloy’s corrosion behaviour is the length of the incubation period. The changes in elemental composition undergone at the alloy surface during corrosion have been investigated using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDX). The results support the literature in that type II corrosion exhibits no preferential alloy depletion underneath the corrosion deposits.Item Open Access Impact of deposit recoat cycle length on hot corrosion of CMSX-4(Springer, 2017-04-05) Sumner, Joy; Aksoul, Quentin; Delgado, Joemar; Potter, Andrew; Gray, SimonHot corrosion causes significant problems for both aerospace and power generation industries, where the combination of high temperature, corrosive gases, and contaminants severely limits component operating lifetimes in gas turbine hot gas streams. Multiple laboratory testing methodologies exist to study this hot corrosion, and these can be affected by a range of variables. This paper investigated the impact of varying deposit recoat cycle length when using the ‘deposit recoat’ testing method. CMSX-4 samples were exposed to simulated type II (pitting) hot corrosion conditions, with the same overall deposit load (averaged across the total exposure run), but different deposit recoat cycles. Post-exposure, samples underwent dimensional metrology analysis to compare metal loss resulting from different deposit recoat cycle lengths. Results for CMSX-4 suggest very small differences in corrosion losses, indicating CMSX-4 hot corrosion datasets obtained from deposit recoat experiments with different deposit recoat cycle lengths can be compared with confidence.Item Open Access Modeling gas turbine materials’ hot corrosion degradation in combustion environments from H2‐rich syngas(Wiley, 2016-09-07) Sumner, Joy; Potter, Andrew; Simms, Nigel J.; Oakey, JohnComponents of gas turbines (such as blades, vanes, combustor cans) exposed to combustion environments at high temperature are susceptible to hot corrosion attack. To successfully plan maintenance and to determine whether to operate in novel combustion modes (e.g., in integrated gasification combined cycles that incorporate pre-combustion carbon capture) predictions of hot corrosion component life must be made. In this paper, hot corrosion datasets relating to two alloys, MarM 509 (a cobalt-based superalloy), and Rene 80 (a nickel-based superalloy) form the basis of hot corrosion predictive lifetime models. The model framework is based on the two stages of incubation and propagation, with the transitions from incubation to propagation around the samples being based on Weibull statistics. The impact of a range of temperatures (including 700 and 900 °C), gas compositions (simulating the combustion of natural gas, H2-rich syngas, or partially cleaned syngas), and deposit chemistries/fluxes have been assessed. Predictions have been made including the expected damage spread for a range of different exposure conditions.Item Open Access The role of superalloy precipitates on the early stages of oxidation and type II hot corrosion(2017-10-07) Potter, Andrew; Sumner, Joy; Nigel, SimmsTo meet materials challenges encountered in gas turbines, superalloys have been developed for high temperature, strength, oxidation and corrosion resistance. One strengthening method is using refractory metal additions to form carbide precipitates. However, such precipitates may be detrimental to the alloy’s environmental resistance. This paper reports how refractory metal carbide precipitates affect the early stages of oxidation and hot corrosion of two alloys: Rene 80 (nickel-based) and MarM 509 (cobalt-based). Samples were exposed at 700 °C in either dry synthetic air or 90 ppm SOx, 10·5% CO2, 8·5% O2, 5% H2O (balance N2) with a 80/20 (Na/K)2SO4 deposit (1·5 μg/cm2/hour flux). The oxidation morphology and corrosion products were investigated by scanning electron microscope and energy dispersive X-ray analysis, to show that refractory metal carbide precipitates close to the metal surfaces disrupt protective oxide scale formation, thus providing inward transport routes for corrosive species.