Molten Slag Research Articles

Optimize the Operation Parameters in Surging Auxiliary Slag Skimming Process Based on Large Eddy Simulation –Volume of Fluid –Discrete Phase Model Coupled Model

A transient 3D mathematical model is developed to study the surging auxiliary slag skimming process in molten iron ladle. A new mathematical model using the large eddy simulation is built for the gas–metal–slag three‐phase flow in the ladle. The Eulerian volume of fluid model is used for tracking the liquid–slag–air free surfaces, and the Lagrangian discrete phase model is used for describing the bubble movement. The procedure of bubble coming out of the liquid and getting into the air is modeled using a user‐defined function. The results show that optimizing the distance of the lance L and the injection volume Q can better the shape of the slag eye, increase the curvature radius of the slag eye on the side of the iron mouth, and broaden the area of the slag eye. At the same time, it can also improve the fluctuation of the slag layer and the liquid surface of molten iron, and reduce the splashing of molten iron and slag entrapment phenomenon, thus improving the slag skimming efficiency.

Novel cost-effective oxygen-enriched melting method for MSWI fly ash

ABSTRACT Herein, a novel oxygen-enriched melting process for fly ash, which uses the biogas produced from the leachate of municipal solid waste incineration (MSWI) plants, is proposed to reduce the high cost of conventional fly ash – melting technology. The fly ash composition was estimated via X-ray fluorescence analysis; the six constituent elements detected in fly ash in the decreasing order of their content were calcium, chlorine, silicon, sulfur, sodium, and potassium. Based on literature and actual production data, the average yield of the leachate was 15% of the total waste entering the MSWI plants and the COD of leachate was 30,000–75,000 mg/L. The amount of biogas that can be used per ton of fly ash was calculated to be 62.0–157.0 m3. The analysis of melting thermal equilibrium revealed the amount of biogas required per ton of fly ash as 57.8 m3. The aforementioned research findings indicate that the biogas produced by MSWI plants can successfully meet the demands of the oxygen-enriched melting of fly ash produced in these plants. By establishing an oxygen-enriched-melting pilot platform, the pilot tests of melting were conducted on fly ash; the results revealed the good melting effects of fly ash. The X-ray diffraction analysis of the slag demonstrated that the content of the vitreous body met the technical requirements for glassy substances. Furthermore, the leaching toxicity test results revealed that heavy metals were well solidified in the slag. This study presents a novel fly ash – melting scheme for MSWI fly ash, namely, biogas oxygen-enriched melting strategy, which has the advantages of technical feasibility and cost-effectiveness. The proposed technique exhibits considerable prospects for widespread application in MSWI plants in China and can play an important role in the safe disposal of fly ash. Implications: In this paper, a low-cost melting method of municipal solid waste incineration(MSWI) fly ash is proposed. This method uses the biogas generated by MSWI plant itself as fuel for melting. Through research, it has been found that the production of biogas can meet the demand for fly ash melting. Adopting biogas as a molten fuel can significantly reduce the cost of melting, thereby significantly reducing the cost of fly ash melting. This study established a pilot scale platform for the melting of biogas and conducted pilot scale experiments on fly ash and additives. The experimental results showed that the melting system operated well and achieved the vitrification of fly ash. The leaching test results of the molten slag showed that heavy metals were well solidified in the slag. The research results can be extended to the MSWI plant for application, which can significantly reduce the cost of fly ash melting disposal, and has broad application prospects.

Numerical Simulation of Heat Transfer of Roller Slag in Centrifugal Preparation of Inorganic Fiber

The synergistic preparation of aluminum silicate ceramic fibers from dust removal ash and fly ash is a newly developed process that achieves green and high added value treatment of solid waste. In this process, the centrifugal fiber forming method is used to treat molten slag to obtain aluminum silicate ceramic fibers. During the production process, the centrifugal roller, as a key component in fiber forming, is in long-term contact with high-temperature slag. The heat transfer between the two causes a huge temperature gradient inside the roller material, causing significant thermal stress inside the material, which has a significant impact on the stability of the centrifugal roller structure and its working condition. This article mainly conducts numerical simulation research on the heat transfer between the roller and the slag during the centrifugal fiber forming process, providing theoretical support for ensuring the structural stability of the roller and improving its service life. The research was carried out using the FLUENT module of the ANSYS software (V2021R1), and the heat transfer model of the slag and roller was established. The effects of the internal circulating water, different slag temperatures, different slag film widths, and different boundary layer thicknesses on the heat transfer of the roller were analyzed. The results show that the water temperature at the outlet is about 6 °C higher than that at the inlet on average; when the temperature of the slag increases by 1 °C, the temperature of the roller surface in contact with the slag increases by 0.91 °C; when the width of the slag on the roll surface is 11–17 mm and the slag thickness (boundary layer thickness) is less than 1 mm, it is beneficial for fiber production.

Microstructure and Mechanical Properties of Modified M2 High‐Speed Steel by Adding La2O3 in the Electroslag Casting Process

An electroslag casting method is used to add rare‐earth La to M2 high‐speed steels by adding La2O3 into the molten slag. The effects of the La content on the microstructure and mechanical properties of M2 high‐speed steel are studied. The results show that rare‐earth La is effectively added to steel by taking advantage of the decomposition of La2O3. The rare‐earth La partially modifies the pre‐existing oxide and sulfide inclusions into small and spherical rare‐earth oxysulfide inclusions. By adding an appropriate amount of La, the as‐cast iron dendrite matrix and coarse eutectic carbides can be refined, the carbide content is reduced, the carbide network is broken, and the decomposition of M2C into M6C and MC is promoted. After heat treatment, the network breaking and spheroidalization of the carbides are further facilitated, and the carbide content is reduced. The impact toughness and bending strength of the studied samples are improved by modifying the inclusions and optimizing the microstructure.

An efficient approach to utilize copper smelting slag: Separating nonferrous metals and reducing iron oxide at high temperature

Over 50 million tons of copper slag are produced worldwide annually. Stacking is currently the primary method used to treat copper slag, resulting in resource wastage and environmental issues. Using slag as a raw material in the steel industry is areasonablesolution. However, the presence of nonferrous metals degrades steel performance and corrodes smelting equipment, and the remaining slag poses environmental and sustainable challenges. Thus, this study focused on removal of nonferrous metals from copper slag and subsequent reduction of iron oxide. The experimental results showed that increasing the percentage of the chlorinating agent (calcium chloride), temperature, and duration, the removal percentage of copper initially increased linearly, then plateaued. The acidity coefficient had a marginal effect on copper removal percentage. The optimum chlorination roasting conditions were 13 % calcium chloride, 1373 K, and 0.5 h, resulting in removal percentages of 90.3 %, 81.9 %, and 82.7 % for copper, zinc, and lead, respectively. The appropriate oxygen partial pressure for chlorination roasting was 10-5–0.7 atm. The reduction percentage of iron oxide was approximately 82 % under roasting conditions of 1.5 h at 1373 K. Based on these results, a novel scheme for copper slag utilization is proposed that involves chlorination roasting for nonferrous metal removal, reduction roasting for iron oxide reduction, and melting to obtain molten iron and separate molten slag. The iron and slag are used for steel manufacturing and rock wool preparation, respectively. This scheme provides apromisingway to efficiently use copper slag, which will reduce primary resource consumption and pollution.

A novel approach for the resource utilization of zinc-bearing dust and sludge via the blast furnace main trough

Minimizing the environmental impact of zinc-bearing dust and sludge (ZDS) while efficiently extracting valuable metals from its intricate mix has become a pressing issue for steel mills. To facilitate comprehensive ZDS usage, we propose a novel approach for recycling ZDS in the blast furnace main trough. This work explores the self-reduction reaction principles of carbon-containing pellets derived from ZDS. Moreover, it examines the consequent alterations in the physical and chemical properties of molten iron and slag. The molten iron temperature inversely correlates with the number of added pellets; the temperature declines as more pellets are introduced. To restrict the molten iron's temperature decrease to within 30℃, it is advisable to limit the quantity of pellets added to 20 kg per ton of molten iron. At 1500℃, the self-reduction reaction of the pellet initiates 1.5 min post its introduction into the molten iron and concludes 12 min thereafter. The pellet mass percentage entering the molten iron is 32 %, whereas the mass percentage of iron elements within the pellet entering molten iron is 64 %. The pellet addition results in an uptick in blast furnace slag viscosity, yet it remains within an acceptable viscosity range (<1Pa·s).

Copper-Bearing Magnetite and Delafossite in Copper Smelter Slags

The cooling paths and kinetics in the system Cu-Fe-O are investigated by the empirical micro- and nanoscale analysis of slags from the flash furnace smelter at Olympic Dam, South Australia. We aim to constrain the exsolution mechanism of delafossite (Cu1+Fe3+O2) from a spinel solid solution (magnetite, Fe3O4) and understand why cuprospinel (CuFe2O4) is never observed, even though, as a species isostructural with magnetite, it might be expected to form. Flash furnace slags produced in the direct-to-blister copper smelter at Olympic Dam contain four Cu-bearing phases: Cu-bearing magnetite, delafossite, metallic copper, and cuprite. Delafossite coexists with magnetite as rims and lamellar exsolutions, as well as bladed aggregates, associated with cuprite within Si-rich glass. The empirical compositions of magnetite and rim delafossite are (Fe2+6.89Cu2+0.86Co0.13Mg0.15Si0.02)8.05 (Fe3+15.52Al0.41Ti0.01Cr0.01)15.95O32, and (Cu1+0.993Co0.002Mg0.002)0.997(Fe3+0.957Al0.027Ti0.005Si0.004)0.993O2, respectively. The measured Cu content of magnetite represents a combination of a solid solution (~6 mol.% cuprospinel endmember) and exsolved delafossite lamellae. Atomic-resolution high-angle annular dark field scanning transmission electron microscope (HAADF STEM) imaging shows epitaxial relationships between delafossite lamellae and host magnetite. Defects promoting the formation of copper nanoparticles towards the lamellae margins suggest rapid kinetics. Dynamic crystallization under locally induced stress in a supercooled system (glass) is recognized from misorientation lamellae in delafossite formed outside magnetite grains. The observations are concordant with crystallization during the cooling of molten slag from 1300 °C to &lt;1080 °C. Melt separation through an immiscibility gap below the solvus in the system Cu-Fe-O is invoked to form the two distinct delafossite associations: (i) melt-1 from which magnetite + delafossite form; and (ii) melt-2 from which delafossite + cuprite form. Such a path also corroborates the published data explaining the lack of cuprospinel as a discrete phase in the slag. Delafossite rims form on magnetite at a peritectic temperature of ~1150 °C via a reaction between the magnetite and copper incorporated in the oxide/Si-rich melt. The confirmation of such a reaction is supported by the observed misfit orientation (~10°) between the rim delafossite and magnetite. HAADF STEM imaging represents a hitherto underutilized tool for understanding pyrometallurgical processes, and offers a direct visualization of phase relationships at the smallest scale that can complement both experimental approaches and theoretical studies based on thermodynamic modelling.

Settling Flow Details in the Flash Smelting Furnace—A CFD-DEM Simulation Study

The flash smelting furnace has previously been simulated using computational fluid dynamics (CFD). A new approach is to combine CFD and the discrete element method (DEM) for more detailed simulations of the different phenomena that occur as copper matte droplets settle through a slag layer. One of the most important phenomena found is the formation of a channeling flow which carries matte droplets faster through the slag. However, such phenomena cannot be directly observed in the flash smelting furnace settler due to the extreme temperatures of the opaque molten slag inside the furnace, therefore alternative methods are required for validating the phenomenon. In this work, the simulated channeling flow is validated with a sphere–oil model. The phenomenon was similar in all of the studied cases, although in the experimental setup the spheres settled faster in the oil model than in the simulations. The differences were most likely caused by the cohesion of the spheres and slight differences in the properties provided by the manufacturer and real properties for the oil and the spheres, and by the fact that simulation ignores surface tension and changing air–oil and water–oil interfaces.

The Melting Mechanism of Hydrogen Direct Reduced Iron in Liquid Slag

The heating and melting of hydrogen direct reduced iron (H‐DRI) in liquid slag is investigated experimentally at 1923 K. For the experiments, slags comprising the CaO‐SiO2‐MgO‐FeO‐Al2O3 system are first premelted at 1923 K in alumina crucibles. The molten slag bath is subsequently used to submerge samples of 7 g of H‐DRI with different degrees of reduction (90.4–99.8%). Following the submersion, the slag bath and the H‐DRI sample are quenched at different times (5–10 s). It is found that the liquid slag penetrates the porous network of the H‐DRI. The penetration is found to increase with lower reduction degrees. The reaction‐enhanced capillary action theory is proposed to explain the dependence. The reasoning is validated by a cold model consisting of a quartz capillary, water, and solid sugar. The slag penetration also enhances the heat transfer and the dephosphorization rate. The present findings can, therefore, aid in optimizing the hydrogen‐based steelmaking route.

Rod-like h-BN modified low carbon Al2O3-C refractory and its high-temperature service performances

Rod-like h-BN with an average diameter of 2 µm was synthesized at a relatively low temperature of 1200 °C through a catalytic pyrolysis precursor strategy using boric acid and melamine as starting materials, and Co(SO3NH2)2·4 H2O as a catalyst precursor. Subsequently, novel low-carbon Al2O3-C refractories were prepared via a replacement of the graphite with the as-synthesized rod-like h-BN. When 1 wt% h-BN rods were added to replace graphite, after 3 h coking at 1400 °C, the cold modulus of rupture, cold compressive strength, oxidation resistance, and thermal shock resistance of the specimen were increased by 16.4%, 24.8%, 31.2%, and 52.2%, respectively, compared with these of the control specimen. Moreover, the introduction of h-BN rods in the matrix enhanced the non-wetting ability of the refractory with molten slag, thus the rod-like h-BN modified low carbon refractory presented better slag corrosion resistance with reference to the specimen without h-BN rods.

Clean preparation of rutile from Ti-containing mixed molten slag by CO2 oxidation

Abstract The effects of SiO2 and CO2 on the crystallization action of Ti-containing mixed molten slag (molten Ti-containing blast furnace slag and molten Ti slag) were discussed by thermodynamic calculation and specific experiments. The results of thermodynamic calculation indicated that the increase of SiO2 addition mass and CO2 oxidation time can promote the transformation of anosovite and sphene to rutile. The experiment results showed that the phase composition of modification slag was only rutile under the SiO2 addition mass of 110 g and the CO2 oxidation time of 180 s. Moreover, the formation theory of rutile was investigated. Using CO2 as an oxidizing gas can not only prepare rutile but also achieve carbon neutrality, which is a clean preparation method.

CONVERSION OF ANTHRACITE BOILER UNITS OF CHP PLANTS FOR COMBUSTION OF SUB-BITUMINOUS COAL IN THE WAR CONDITIONS

The work describes the task of urgently converting the boilers of anthracite-burning combined heat and power plants to sub-bituminous coal, which arose in the conditions of Russian aggression in connection with the complete cessation of supplies of project fuel. The developed methods of solving it in a short time with the maximum use of available equipment are given, using the example of boilers with a steam capacity of 220 t/h of CHPP «EURO-RECONSTRUKTSIA» LLC (Darnytska CHPP, Kyiv). On the basis of calculation justification it is shown, and the tests and operation have confirmed, the safety and effectiveness of the technical solution with preservation of coal drying by hot air while limiting the temperature at the exit of the mill and with pulverized coal transport to the burners by half-heated air taken after the first stage of the air heater, while reducing the diameter of the pulverized coal pipes. Measures are proposed and implemented to equalize the distribution of pulverized coal and air among the burners, to operate the mills in alternating mode with the aim to increase the use of hot air, correspondingly to increase the coal jet temperature, to improve the conditions of molten slag removal and to reduce the temperature of flue gases, etc. Uninterrupted operation of the Darnytska CHPP became an important factor in ensuring the functioning of the critical infrastructure of heat and energy supply of Kyiv in conditions of enemy shelling. Bibl. 18, Fig. 5, Tab. 4.

Transforming Cl-Containing Waste Plastics into Carbon Resource for Steelmaking: Theoretical Insight.

The accumulation of waste plastics poses a significant environmental challenge, leading to persistent pollution in terrestrial and aquatic ecosystems. A practical approach to address this issue involves the transformation of postconsumer waste plastics into industrially valuable products. This study focuses on an example of harnessing the carbon content in these polymers for carbon-demanding industrial processes, thereby reducing waste plastics from the environment and alleviating the demand for mined carbon resources. Employing quantum simulations, we examine the viability of polychloroprene as a carburizing agent in the steelmaking process. Our simulations reveal that polychloroprene exhibits excellent carbon diffusivity in molten iron, with a theoretical diffusion coefficient of 8.983 × 10-5cm2 s-1. This value competes favorably with that of metallurgical coke and surpasses the carbon diffusivity of other polymers, such as polycarbonate, polyurethane, and polysulfide. Additionally, our findings demonstrate that the chlorine content in polychloroprene does not permeate into molten iron but instead remains confined to the molten iron and slag interface.

Motion and dispersion characteristics of graphite particles in a bottom-blown converter for molten slag reduction

In order to improve the recovery of iron resource in molten basic oxygen furnace (BOF) slag through carbothermal reduction, bottom blowing argon gas is used to promote the mixing efficiency between molten slag and graphite particles in the converter. In the present work, computational fluid dynamic-discrete particle model (CFD-DPM) method coupled with the reduction kinetic model of FeO in molten slag by graphite particle is employed to simulate the multiphase system composed of molten slag, graphite particle and argon gas. The motion and dispersion characteristics of graphite particles in a bottom-blown converter were mainly investigated, and the decrease of graphite particle diameter caused by the reduction reaction was considered. A particle dispersion index was also proposed to evaluate the distribution uniformity of graphite particles in the molten slag. In addition, the effects of initial particle diameter and bottom tuyere arrangement on the dispersion characteristics of graphite particles were further discussed. The results show that the proportion of large-sized particles is higher in the inactive-flow zone and the motion trajectory of graphite particles can be divided into two regimes. Graphite particles with an initial diameter of 5 mm and the converter with six bottom-blown tuyeres are more conducive to the homo-dispersion of graphite particles.

Corrosion behavior of CaO–Al2O3–SiO2–MgO-Cr2O3 slag on MgO refractory brick for smelting of chromite

The MgO bricks were generally used as the refractory linings in electric furnace smelting of chromite ore. The reaction mechanisms between the MgO refractory and CaO-Al2O3-SiO2-MgO-Cr2O3 slags were experimentally investigated. The elemental distribution and phase compositions at the contact surface between slags and refractory bricks were studied using thermodynamic calculations and SEM-EDS techniques analysis. The main phase of the refractory brick was MgO, while the main phases of slag were pyroxene ((Ca, Mg) AlSi2O6), chromium spinel (Mg (Al, Cr)2O4), and magnesium olivine (2MgO·SiO2). The EDS analysis showed that the main phases at the contact surface of slag and refractory brick were calcium magnesium olivine and magnesium olivine, and the proportion of calcium magnesium olivine phase increased with the increase of slag basicity. Furthermore, the thermodynamic calculation indicated that the melting temperature and the slag viscosity decreased with the increase of slag basicity, and then the molten slag more easily penetrated the pores of refractory brick and caused brick corrosion.

Co-treatment of diamond-wire-saw silicon kerf and spent automotive catalysts for simultaneous recovery of PGMs, REEs, Zr, and high-purity Si

Spent automotive catalysts (SACs) and diamond-wire-saw silicon kerf (DWSSK) are classified as hazardous wastes. Currently, the two wastes are treated separately using unrelated approaches. More than two independent approaches are required to recover platinum group metals (PGMs), Zr and rare earth elements (REEs) from SACs, and recover Si from DWSSK, which is time-consuming and laborious. In this study, a new approach was proposed to co-treat the two wastes based on the concept of using waste treats waste: using DWSSK (∼89.85 wt% Si) as a new metal collector to extract PGMs, REEs, and Zr simultaneously from SACs to obtain a Si-VM alloy (VM: valuable metal); meanwhile, using the carrier of SACs to form molten slag to eliminate the main impurity, O, from DWSSK. The largest recovery ratios of Pd, Rh, Zr, Ce, La, and Nd from SACs were 99.50 ± 0.10%, 99.14 ± 0.14 %, 96.19 ± 0.76%, 67.18 ± 4.57%, 61.24 ± 4.93% and 47.65 ± 7.27%, respectively, and the largest removal ratio of O from DWSSK was 99.96%. After smelting, the Si-VM alloy was separated into high-purity Si and VM-containing acid solutions via acid leaching. The leaching ratios of Pd, Rh, Ce, La, Nd, and Zr were 99.78%, 98.15%, 99.93%, ∼100%, 99.76% and 99.98%, respectively. The purity of Si was upgraded from 89.85 wt% (in DWSSK) to 99.98 wt% after acid leaching. The new approach proposed in this study is considered more environmentally friendly and cost-effective than the regular approaches that treat the two wastes separately.

From waste to wealth: Valuable metals recovered from waste tungsten leaching residue by a smelting reduction process using CaO-Fe capture agent

Tungsten leaching residue (W-residue), a hazardous waste generated from the industrial recovery of the spent tungsten carbides, poses a threat to the environment. The W-residue contains high grades of SiO2 and TiO2 oxides, and low grades of high-value metal oxides such as WO3, CoO, Ta2O5, and Nb2O5. Herein, a smelting reduction process was proposed to effectively recover the high-value metals from the W-residue and obtained a medium-entropy carbide (MEC) composite. During the smelting process, the valuable metals were recovered as alloy consisting of (Fe, Co)-rich silicide, (Fe, Cr, W)-rich silicide, and (W, Ta, Nb, Ti)C, respectively. The addition of flux CaO lowered the liquidus temperature of the molten slag, and effective alloy-slag phase separation was achieved by adding Fe as a metal collector to capture the alloy droplets entrapped in the slag. Under the optimal conditions, the total recovery rate reached 86.8%. Moreover, the obtained (W, Ta, Nb, Ti)C as MEC exhibited a Vickers hardness of over 19 GPa and can be used as a wear-resistant alloy. This study proposed a strategy for extracting high-value metals from hazardous tungsten residue, which could complement existing recycling processes towards a closed-loop process in the tungsten industry.

Investigation of SiC formation on the graphite surface by CO-H2-SiO gas

FINEX process, which utilizes hydrogen (H2) as a part of reductants, has emerged as an environmentally sustainable ironmaking process to meet the upcoming carbon-neutral era. In the H2-enriched atmosphere, local slag holdup in the carbonaceous particle bed may increase due to the increased melting temperature of slags by the rapid reduction of iron oxide and the resulting lower wettability of the carbonaceous materials by liquid slag. In-situ SiC formation on the carbon surface gains much attention as a method to reduce the slag holdup. In this study, as a fundamental study, we investigated the SiC formation on the surface of a graphite substrate under a CO-H2-SiO gas environment at 1873 K. It was found that as the partial pressure of H2 increased, the penetration depth of a SiC layer formed on the graphite surface increased, and the surface roughness became enhanced. A reaction rate analysis revealed that the H2-CO gas mixture accelerated the SiC formation on the graphite surface compared to the N2-CO gas mixture. This effect was attributed to the high bimolecular diffusivity of H2-CO. Our results demonstrate that under a CO-H2-SiO gas environment, the fast diffusion of H2 gas through micropores in the graphite significantly enhances the formation of SiC on the graphite surface. The results obtained in this study show that the acceleration of SiC formation under an H2-enriched atmosphere would improve the wettability of molten slag and reduce the slag holdup in the FINEX process.

Composition-specific granulation characteristics of molten slag at improved throughput and high temperature of 1,723 K

Centrifugal granulation is one key step to enable waste heat recovery from the molten slag in the iron and steel industry. Yet, it remains unknown about the granulation characteristics of molten slag with different chemical compositions, especially at high throughput. In this work, we provided an experimental study on centrifugal granulation with four types of molten slags. The stage-specific centrifugal granulation was recorded and analyzed at first. Both effects of atomizer configuration and chemical compositions on granulation were investigated in detail. The cup-type atomizer favors film-mode disintegration and possesses better anti-adhesion capacity although the final granule size was not strongly affected by the atomizer configuration. Most importantly, centrifugal granulation has been demonstrated with appreciable adaptability to composition-specific blast furnace (BF) slag with binary basicity of 0.9–1.3. The present study not only sheds light on the modest effect of the chemical composition of molten slag on centrifugal granulation characteristics, but also gains credit for the adaptivity of CGATER.

Failure analysis of blowholes in welded boiler water walls

Water walls are subjected to thermo-mechanical loading, which potentially leads to fatigue crack initiation and growth from the weld defects. This study comprehensively analyzes the blowout failure (blowholes) occurring in boiler water walls. An experimental-simulation mixed approach has been adopted to establish the effect of weld defects on fatigue crack initiation, crack growth, and ultimate failure by blowhole. The effect of the defect position on the propagation and failure has also been modeled by extended Finite Element Method (XFEM) based on the criteria of energy release rate. A combination of XFEM and Direct Cyclic Analysis (DCA) is used to calculate low-cycle fatigue life. The cracks are shown to have originated from lack-of-fusion defects, causing the membrane to disconnect and reducing heat transfer efficiency, which may lead to localized thermal hotspots and membrane rupture, leaving molten slag residues on the airside of water walls.