Browsing by Author "Sumner, Joy"

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    Analysis of combined static load and low temperature hot corrosion induced cracking in CMSX-4 at 550°C
    (Elsevier, 2019-10-18) Brooking, Laurie; Gray, Simon; Dawson, K.; Nicholls, John R.; Simms, Nigel J.; Sumner, Joy; Tatlock, G. J.
    A CMSX-4 3-point bend specimen was statically loaded under hot corrosion conditions and SEM, (S)TEM and EDX techniques were used to analyse the cracking generated. Sulphur, chlorine, sodium and oxygen were found at the crack tip, and an influence of loading on the corrosion mechanism’s preference to interact with either the γ or γʹ was observed. The microscopy analysis is in support of the corrosive mechanism being a combined stress and electrochemical corrosion linked with low temperature hot corrosion, where crack propagation occurs as a result of localised corrosion enhanced material degradation. High magnification EDX mapping identified W as segregating to the γʹ at room temperature.
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    Analysis of the effect of a series of back twist blade configurations for an active pitch-to-stall floating offshore wind turbine
    (American Society of Mechanical Engineers, 2020-04-08) Ward, Dawn; Collu, Maurizio; Sumner, Joy
    For a turbine mounted on a floating platform, extreme induced loads can be increased by up to 1.6 times those experienced by a turbine situated on a fixed base. If these loads cannot be reduced, towers must be strengthened which will result in increased costs and weight. These tower loads would be additionally exasperated for a pitch-to-feather controlled turbine by a phenomenon generally referred to as “negative damping,” if it were not avoided. Preventing negative damping from occurring on a pitch-to-feather controlled floating platform negatively affects rotor speed control and regulated power performance. However, minimizing the blade bending moment response can result in a reduction in the tower fore-aft moment response, which can increase the tower life. A variable-speed, variable pitch-to-stall (VSVP-S) floating semi-submersible wind turbine, which does not suffer from the negative damping and hence provides a more regulated power output, is presented. This incorporates a back twist blade profile such that the blade twist, starting at the root, initially twists toward stall and, at some pre-determined “initiation” point, changes direction to twist back toward feather until the tip. Wind frequency weighting was applied to the tower axial fatigue life trends of different blade profiles and a preferred blade back twist profile was identified. This had a back twist angle of −3 deg and started at 87.5% along the blade length and achieved a 5.1% increase in the tower fatigue life.
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    An approach to evaluating the impact of contaminants on flux deposition in gas turbines
    (Springer, 2023-08-18) Mori, Stefano; Mendil, Mathilde; Wells, Jonathan; Chapman, Neil; Simms, Nigel; Wells, Roger; Sumner, Joy
    Gas turbines are a key part of many countries’ power generation portfolios, but components such as blades can suffer from hot corrosion attack, which can decrease component lifetimes. Corrosion is driven by impurity levels in the fuel and air (e.g., species containing sulphur and/or alkali metals) and depends on environmental conditions (e.g., air pollution, seawater droplets), that can lead to formation of harmful species in the gas. Understanding and determining the deposition flux of such contaminants is crucial for understanding the problem. Thermodynamic simulations were used to determine types and amounts of potentially corrosive contaminants, this was followed by deposition fluxes calculations. An operating scenario, based upon an offshore platform was evaluated. The effectiveness of different filtration systems has been evaluated. The impurity levels of alkali metals, such as sodium, greatly impacts the calculated deposition flux of species linked to corrosion attack. The presence of Na2SO4, and K2SO4 was found, at temperature representative of stage 2 nozzle guide vanes. Lowering sulphur input (from fuel or air) can be an efficient way to decrease deposition, attention must also be paid to lowering the amount of alkali metal entering the gas turbine, which can be lowered by the filtration systems’ correct use.
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    Approaches to modelling fireside corrosion of superheater / reheater tubes in coal and biomass fired combustion power plants
    (ASM International, 2019-10-24) Simms, Nigel J.; Ekpe, Blessing; Riccio, Chiara; Mori, Stefano; Sumner, Joy; Oakey, John E.
    The combustion of coal and biomass fuels in power plants generates deposits on the surfaces of superheater / reheater tubes that can lead onto fireside corrosion. This type of materials degradation can limit the lives of such tubes in the long term, and better methods are needed to produce predictive models for such damage. This paper reports on four different approaches that are being investigated to tackle the challenge of modelling fireside corrosion damage on superheaters / reheaters: (a) CFD models to predict deposition onto tube surfaces; (b) generation of a database of available fireside corrosion data; (c) development of mechanistic and statistically based models of fireside corrosion from laboratory exposures and dimensional metrology; (d) statistical analysis of plant derived fireside corrosion datasets using multi-variable statistical techniques, such as Partial Least Squares Regression (PLSR). An improved understanding of the factors that influence fireside corrosion is resulting from the use of a combination of these different approaches to develop a suite of models for fireside corrosion damage.
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    Assessment of corrosive attack of Fe9Cr1Mo alloys in pressurised CO2 for prediction of breakaway oxidation
    (Elsevier, 2023-07-27) Gong, Yilun; Gill, Simon P. A.; Yan, Sabrina; Higginson, Rebecca; Sumner, Joy; Simms, Nigel J.; Larsson, Henrik; Shin, Aya; Pearson, Jonathan M.; Young, David J.; Atkinson, Colin; Cocks, Alan C. F.; Reed, Roger C.
    To provide clarity on the poorly-understood mechanism of breakaway oxidation, corrosion of Fe9Cr1Mo steel in pressurised CO is quantified and modelled. The temperature range 400–640 , relevant to nuclear power plants, is emphasised. Attack is in the form of combined oxide scale growth and internal carburisation of the metal. Carbon activity in the metal at its surface exhibits a strong time dependence consistent with the kinetically-limited transport of carbon due to the slow Boudouard reaction. Breakaway is associated with the approach to saturation of the steel with respect to carbon. Diffusion modelling agrees well with steel carbide precipitation observations.
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    Causal discovery to understand hot corrosion
    (Wiley, 2024-02-12) Varghese, Akhil; Arana-Catania, Miguel; Mori, Stefano; Encinas-Oropesa, Adriana; Sumner, Joy
    Gas turbine superalloys experience hot corrosion, driven by factors including corrosive deposit flux, temperature, gas composition, and component material. The full mechanism still needs clarification and research often focuses on laboratory work. As such, there is interest in causal discovery to confirm the significance of factors and identify potential missing causal relationships or codependencies between these factors. The causal discovery algorithm fast causal inference (FCI) has been trialled on a small set of laboratory data, with the outputs evaluated for their significance to corrosion propagation, and compared to existing mechanistic understanding. FCI identified salt deposition flux as the most influential corrosion variable for this limited data set. However, HCl was the second most influential for pitting regions, compared to temperature for more uniformly corroding regions. Thus, FCI generated causal links aligned with literature from a randomised corrosion data set, while also identifying the presence of two different degradation modes in operation.
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    Combined hot corrosion and static stress or fatigue of single crystal superalloys.
    (2018-09) Brooking, Laurie Finian; Sumner, Joy; Gray, Simon; Simms, Nigel J.
    It has been observed that gas turbine (GT) blades operating in harsh environments can undergo material degradation in the form of crack initiation and propagation before that predicted by fatigue lifing. It is thought that this degradation can occur partly as a result of the growing demands for improved GT efficiencies. This is because the requirement for improved GT efficiencies is commonly achieved through increases in operational temperatures and pressures which the turbine stages operate at. These increases in the operational temperatures can consequently lead to the extended effect of hot corrosion in locations of the blade which would not normally impacted, such as the under platform region. Therefore, GT blades are subjected to continuous developments in terms of blade design and material properties and selection in order to achieve improvement in the GT efficiencies, reduce emissions and lower life cycle costs. However, at start of this research project it was postulated that the mechanism causing premature material degradation is a result of the extended effects of low temperature hot corrosion (LTHC), interacting with both cyclic and static loading conditions. In order to experimentally study these interactions statically and cyclically loaded specimens were tested in environments representative of the under platform region of both industrial and aviation gas turbine (GT) blades. A range of geometries were studied: C-rings, three point bend and cylindrical fatigue specimens. Using these specimens experimental studies were conducted investigating the impact of deposit flux, dwell time, multiaxial stress state and load application rate. Further investigations into the microscopic mechanism occurring at the crack tip have been conducted using high magnification transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Detailed stress state data has been produced using finite element analysis (FEA), this data has then been used to assess the impact of the stress state on crack initiation and propagation. It was found that turbine blade materials were susceptible to a form of high temperature stress corrosion cracking (SCC). Additionally, enhanced fatigue crack initiation and propagation was observed with test conditions consistent with low temperature hot corrosion (LTHC) conditions. There was shown to be a detrimental impact with increased rates of LTHC on the high temperature cracking mechanism. Detailed microscopy and analysis of specimens informed a proposed fundamental mechanism behind the enhanced cracking observed in LTHC environments. The five research papers presented within this thesis provide contributions to knowledge and developments in the understanding of crack initiation and propagation within superalloys exposed to simultaneous LTHC environments and loading.
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    A comparative evaluation of waste wood and herbaceous biomass fireside corrosion behaviours
    (Elsevier, 2022-05-13) Sanusi, Toyin; Sumner, Joy; Simms, Nigel
    Biomass/biomass waste (BBW) is a renewable energy source fired in combustion power plants. However, challenges associated include accelerated ‘fireside’ corrosion of heat exchangers. Fireside corrosion is fuel dependent, e.g. virgin wood fuels have lower fireside corrosion risks; as such their demand and cost is high. Waste wood fuels (WWF) and herbaceous grass biomass (HGB), generate different combustion environments, influencing heat exchanger fireside corrosion damage. This paper compares the fireside corrosion of WWF and HGB fuels to improve understanding of their attack mechanisms on T91 and 374HFG. The species generated in combustion have been investigated by thermodynamic modelling. Corrosion damage has been evaluated by high temperature corrosion furnace tests at 600 °C, employing the well-established deposit recoat method based on these evolved species. Vapour condensation fluxes have been compared for both fuel categories; corrosion rates increase with this condensation flux. Deposition fluxes from HGB fuels are higher than for WWF. For example, the average KCl deposition fluxes calculated are 1566 µg/cm2h and 295 µg/cm2h per kg fuel feed respectively, explaining the comparatively greater fireside corrosion rates experienced in power plants combusting HGB fuels. The deposit chemistries generated are also different: K-containing compounds only (for HGB fuels) versus K-, Na- and Ca-containing compounds (for WWF). Evaluation of corroded samples exposed to the different deposit chemistries show increased corrosion attack to both steels under simulated WWF firing conditions than for the HGB at matched deposit flux (100 µg/cm2h).
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    Corrosion fatigue testing: the combined effect of stress and high temperature corrosion
    (Taylor & Francis, 2017-10-20) Chapman, Neil; Brooking, Laurie; Sumner, Joy; Gray, Simon; Nicholls, John R.
    A corrosive environment can have a detrimental effect on the fatigue life of a material due to a change in failure mechanism. Attempts have been made to replicate this change on nickel-base superalloy CMSX-4 cast in the <001> orientation. Fatigue testing in air, of this material typically produces a fracture on an angle of approximately 55° which is consistent with the fracture having propagated on a {111} slip plane. The aim of the research was to fatigue test in a corrosive environment with the purpose of producing a crack/fracture which deviated from the typical angle and thus confirm that the corrosive environment had affected the fatigue mechanism. It was concluded that the change in mechanism to high temperature corrosion fatigue was associated with a reduced load application rate together with precorroding the test specimens to trigger the initiation of the corrosion fatigue mechanism.
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    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, Joy
    Global 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.
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    Data for the paper titled Analysis of Combined Static Load and Low Temperature Hot Corrosion Induced Cracking in CMSX-4 at 550°C
    (Cranfield University, 2020-02-03 08:09) Gray, Simon; Brooking, Laurie; Nicholls, John; Sumner, Joy; Simms, Nigel; J. Tatlock, Gordon; Dawson, Karl
    Presentation containing figures within the paper
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    Effect of dissolved CO2 on the interaction of stress and corrosion for pipeline carbon steels in simulated marine environments
    (MDPI, 2023-06-22) Abubakar, Shamsuddeen Ashurah; Mori, Stefano; Sumner, Joy
    Offshore pipelines are subjected to stresses (e.g., from fluid flow, mechanical vibration, and earth movement). These stresses, combined with corrosive environments and in the presence of trace gases (O2, CO2), can increase the pipeline’s corrosion rate and potentially lead to cracking. As such, the impact of trace gases such as CO2 (linked to enhanced oil recovery and carbon capture and sequestration) on corrosion is key to determining whether pipelines are at increased risk. American Petroleum Institute (API) 5L X70 and X100 were exposed as stressed C-rings (80% or 95% of yield strength). The tests were conducted with either N2 (control) or CO2 bubbled through 3.5% NaCl, at either 5 °C or 25 °C. Linear polarization resistance was used to assess corrosion rate, while morphology and variation were determined using optical microscopy (generating metal loss distributions) and scanning electron microscopy. The control experiment (N2) showed that corrosion rates correlated with temperature and stress. In this low O2 environment, both alloys showed similar trends. Under CO2 exposure, all samples showed accelerated corrosion rates; furthermore, the morphologies generated were different for the two alloys: undercutting corrosion with discontinuous microcracks (X70) or deep, wide ellipses (X100). Understanding these changes in corrosion response is key when selecting materials for specific operational environments.
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    Effect of stress state and simultaneous hot corrosion on the crack propagation and fatigue life of single crystal superalloy CMSX-4
    (Elsevier, 2018-05-03) Brooking, Laurie; Gray, Simon; Sumner, Joy; Nicholls, John R.; Marchant, G.; Simms, Nigel J.
    Operating conditions within industrial gas turbines are changing in response to pressures to reduce environmental impact and enable use of renewable sources. This is driving an increase in the operational temperatures and pressures of combustion in turbine systems. Additionally, diverse operating environments can result in higher sulphur and trace metal contaminant levels, exacerbating hot corrosion in GT systems. Low cycle fatigue (LCF) cycling can also be intensified as a result of increased start/stop shutdowns. The combined effects of hot corrosion and stress are experimentally studied on CMSX-4 single crystal (SC) γ/γ' system under both fatigue and static stress conditions, with either a multi-axial bending or uniaxial stress state. The associated stress intensity thresholds (KTH) under the various stress conditions were evaluated using finite element analysis (FEA). Cracking was observed both under static and fatigue stress conditions in a hot corrosion environment. Crack morphologies were analysed using SEM techniques. Bending stresses and fatigue cycles demonstrated increased crack propagation in the presence of hot corrosion with static uniaxial stresses showing the longest nucleation times and lowest propagation rates.
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    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, Nigel
    Future 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.
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    Evaluation of the effects of highly saline and warm seawaters on corrosivity of marine assets
    (DECHEMA, 2019-09-13) Abbas, Muntazir; Simms, Nigel; Syed, Ali Sarfaraz; Malik, Owais Ahmed; Sumner, Joy
    In marine environment, the corrosion rate of metallic structures vary remarkably with the change in climatic conditions and seawater composition across geographical locations. The corrosion in brackish and polluted seawaters is even more complicated due to the presence of different chemical species and untreated effluents. The complex correlation between the above average temperature and salinity with the high nutrient content in polluted seawater tends to accelerate the rate of biological activities and microbiological induced corrosion (MIC). This research paper has investigated the short-term corrosion of cupronickel (Cu-Ni) 90/10 alloy, and mild steel in the highly saline and warm seawaters. Field experiments for general corrosion under fully immersed condition were conducted at two site locations, represented as site 1 for pollutantrich seawaters and site 2 for natural seawaters in the North Indian Ocean. The experiments were conducted for a period of up to two months and coupons for each metal alloy were recovered from both sites after an exposure period of 15, 30, 45, and 60 days, respectively. In both environmental conditions, significantly high mass loss and corrosion rates were recorded for each metal alloys. Despite the same temperature of seawater and immersion depth at both sites, average corrosion losses at site 1 were found to be 5 and 3 times higher than that of site 2 for Cu-Ni alloy 90/10, and mild steel coupons, respectively.
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    Fireside and steamside performance in biomass power plant
    (Taylor & Francis, 2022-01-10) Mori, Stefano; Sumner, Joy; Bouvet, Justin; Simms, Nigel J.
    To address the challenge of climate change, the energy sector is developing novel strategies to reduce greenhouse gas emissions. One route is to increase steam temperatures and pressures (above 650°C and 350 bar). Another route is the use of potential net zero emissions fuels, like biomass. Both these routes cause issues for the heat-exchanger materials due to the differences in composition of the combustion environments generated, compared to coal. This paper characterises candidate superheater/reheater alloys’ behaviour (Sanicro 25 and IN740) at 700°C. 1,000 h fireside and 10,000 h steamside exposures were carried out, the first using ‘deposit recoat’ techniques. Sample cross-sections were analysed using dimensional metrology and SEM/EDX. Fireside results for Sanicro 25 showed degradation throughout the samples’ thicknesses. In steamside exposures, Sanicro 25 formed a Cr-rich scale, and Nb rich particles (z-phase). IN740 showed lower metal and sound metal damage than Sanicro 25 for fireside and steam oxidation exposures.
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    Fireside corrosion and deposition on heat exchangers in biomass combustion systems
    (Taylor and Francis, 2022-10-31) Mori, Stefano; Sanusi, Toyin; Simms, Nigel; Sumner, Joy
    To address climate change, power plants need to switch to greener fuels. One possible fuel is biomass; a carbon neutral/low carbon fuel. However biomasses’ chemistries are both different from coal’s and vary depending on their sources, containing unique levels of the trace elements (e.g., Cl and S) capable of altering the degradation of heat-exchangers. As such, an understanding of the effects of these variations on fireside corrosion is needed. Laboratory testing exposed alloys T91 and TP347HFG in a simulated agricultural product combustion environment at 600°C (up to 1000h; 100h cycles). Three different deposits mixtures were investigated (comprised of KCl, K2SO4, Na2SO4, CaSO4 indifferent percentages) mimicking accelerated corrosion from different biomasses. Corrosion behaviour was found to be dependant on both alloy and deposit chemistries, with the two materials showing different responses. The deposit with lowest KCl showed lowest corrosion damage, while the highest KCl deposit showed more aggressive behaviour.
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    Fireside corrosion of heat exchanger materials for advanced solid fuel fired power plants
    (Springer, 2021-12-18) Mori, Stefano; Pidcock, Andy; Sumner, Joy; Simms, Nigel; Oakey, John
    To address the challenge of climate change, future energy systems need to have reduced greenhouse gas emissions and increased efficiencies. For solid fuel fired combustion plants, one route towards achieving this is to increase the system’s steam temperatures and pressures. Another route is to co-fire renewable fuels (such as biomass) with coals. Fireside corrosion performance of two candidate superheater/reheater alloys has been characterised at higher heat exchanger surface temperature. Samples of the alloys (a stainless steel, Sanicro 25 and a nickel-based alloy, IN740) were exposed in fireside corrosion tests at 650 °C, 700 °C and 750 °C, in controlled atmosphere furnaces using the ‘deposit recoat’ test method to simulate superheater/reheater exposure for 1000 h. After exposure, the samples were analysed using dimensional metrology to determine the extent and distributions of corrosion damage in terms of surface recession and internal damage. At 650 °C, the stainless steel and nickel-based alloy performed similarly, while at 700 °C and above, the median damage to the steel was at least 3 times greater than for the nickel-based alloy. Optical and electronic microscopy studies were used to study samples’ damage morphologies after exposure. Intergranular damage and pits were found in sample cross sections, while chromium depletion was found in areas with internal damage. For high-temperature applications, the higher cost of the nickel-based alloy could be offset by the longer life they would allow in plant with higher operating temperatures.
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    Fireside performance of different coatings in biomass power plant
    (Taylor & Francis, 2023-03-12) Mori, Stefano; Pidcock, Andy; Sumner, Joy; Simms, Nigel; Oakey, John
    The energy sector will need to employ novel strategies to reduce greenhouse gas emissions, such as the increase of steam temperatures/pressures or the use of low carbon fuels (i.e. biomass). Both cause heat exchanger materials’ degradation issues, due to the formation of more/different corrosive deposits, which requires the use of expensive nickel-based materials or coatings. This paper focuses on the behaviour of three different coatings (HVOF NiCrFeSi, laser clad FeCrAl and Laser Clad NiCrFeSi) deposited on TP347HFG, at 700°C (up to 1000 h exposure). Tests were performed using the ‘deposit recoat’ method (KCl deposit) in simulated biomass combustion environments. Cross-sections were analysed using dimensional metrology, to determine distributions of metal loss and internal damage. Intergranular damage and pits were identified using SEM/EDX. A ‘diffusion cell’ behaviour was observed, which led to depletion of alloying elements from the coating and consequent increase in damage. The results suggested a severe degradation of all coatings.
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    Formation of corrosive compounds from biomass/waste combustion.
    (2021-08) Sanusi, Toyin; Sumner, Joy; Simms, Nigel J.
    Biomass/waste is a renewable energy source which can be fired in combustion power plants. These fuels can be used to replace coal combustion, with its associated environmental impacts, however challenges associated with biomass include accelerated fireside corrosion of heat exchangers (HX) due to producing different corrosive compounds; i.e. fireside corrosion is fuel dependent. As such compromises may be needed. For example, virgin wood fuels have lower fireside corrosion risks, although alternative biomass/waste fuels are cheaper. This thesis compares the fireside corrosion influences of several biomass/waste fuel categories to further understand their attack mechanisms on conventional HX steels, T91 and 374HFG. The corrosive species generated during the fuels’ combustion have been investigated using thermodynamic modelling by MTData. Corrosion damage has been evaluated using high temperature corrosion furnace tests, conducted with isothermal conditions. In contrast to isothermal test conditions, further testing developed an alteration to the furnace setup to address heat gradient impacts on corrosion damage. In both fireside corrosion methodologies, the well-established deposit re-coat technique has been employed to simulate the deposition of representative salts. To evaluate corrosion trends influenced by the biomass/waste fuels with different exposure parameters, temperature, gas and deposition flux conditions have also been varied. Corrosion data evaluation is both quantitative (dimensional and weight changes of metals samples) and qualitative (scanning electron microscopy and energy dispersive X-ray spectroscopy). Thermodynamic modelling shows higher partitioning of alkali metal species into the flue gas occurs for Wood Waste Fuels (WWF) than for Agricultural Plants & Residues (APR) and Herbaceous Grass Biomass (HGB) fuels. However, APR and HGB fuels release higher absolute amounts of these species in combustion. The high chloride percentages in APR and HGB deposits (69-89 mol.%) do not always correlate with higher corrosion rates as determined in the laboratory tests. Indeed, WWF deposits, with chlorides as low as 30 mol.%, have proven to be more destructive under certain operating conditions. Despite this, the increased deposition flux on plant HXs of corrosive species from HGB and APR firing on plant HXs is responsible for their shorter operational lives as compared to WWF. This has implications for the type of biomass/waste fuel combusted for power generation.