Steam Turbine Blades Research Articles

Hot Workability Investigation of an Fe-Al-Ta Alloy Using Deformation Processing Maps

Fe-Al-Ta alloys are expected to replace high-alloyed steels in steam turbine blades. However, the mechanical properties of the forged blades are still not optimal due to limited grain refinement during hot forging and the coarse-grained microstructure inherited from the as-cast precursor. It is, therefore, essential to investigate the hot deformation behavior of the alloy to identify the optimum range for the deformation parameters leading to good hot workability with significant grain refinement. The hot deformation behavior and hot workability of an Fe-25Al-1.5Ta (at.%) alloy were investigated in the present work using constitutive modeling and the concept of processing maps. Uniaxial compression tests were conducted in a strain rate range from 0.0013 s−1 to 1 s−1 and in a temperature range from 900 °C to 1100 °C, where a disordered A2 α-(Fe, Al) matrix phase along with a C14-(Fe, Al)2Ta Laves phase were confirmed by X-ray diffraction. The flow stress–strain curves showed a broad maximum followed by a slight drop in stress until a steady state was reached. The optimum processing window for the studied alloy was located at 910–1060 °C/0.0013–0.005 s−1, where the efficiency of the power dissipation (η) and strain rate sensitivity (m) reached 50% and 0.33, respectively. The material underwent a combination of dynamic recovery and dynamic recrystallization over the whole tested deformation range. No flow instabilities were predicted based on Prasad’s flow instability criterion when deformation was performed up to a true strain of 0.5 and 0.8, indicating a high degree of hot workability of the studied alloy over the entire deformation range tested. The current study reveals a well-suited parameter range for the safe and efficient deformation of Fe-Al-Ta alloys, which may contribute to the optimization of the thermomechanical processing of this alloy.

The search for an appropriate condensation model to simulate wet steam transonic flows

PurposeThe purpose of this study is to model steam condensing flows through steam turbine blades and find the most suitable condensation model to predict the condensation phenomenon.Design/methodology/approachTo find the most suitable condensation model, five nucleation equations and four droplet growth equations are combined, and 20 cases are considered for modelling the wet steam flow through steam turbine blades. Finally, by the comparison between the numerical results and experiments, the most suitable case is proposed. To find out whether the proposed case is also valid for other boundary conditions and geometries, it is used to simulate wet steam flows in de Laval nozzles.FindingsThe results indicate that among all the cases, combining the Hale nucleation equation with the Gyarmathy droplet growth equation results in the smallest error in the simulation of wet steam flows through steam turbine blades. Compared with experimental data, the proposed model’s relative error for the static pressure distribution on the blade suction and pressure sides is 2.7% and 2.3%, respectively, and for the liquid droplet radius distribution it totals to 1%. This case is also reliable for simulating condensing steam flows in de Laval nozzles.Originality/valueThe selection of an appropriate condensation model plays a vital role in the simulation of wet steam flows. Considering that the results of numerical studies on condensation models in recent years have not been completely consistent with the experiments and that there are still uncertainties in this field, further studies aiming to improve condensation models are of particular importance. As condensation models play an important role in simulating the condensation phenomenon, this research can help other researchers to better understand the purpose and importance of choosing a suitable condensation model in improving the results. This study is a significant step to improve the existing condensation models and it can help other researchers to gain a revealing insight into choosing an appropriate condensation model for their simulations.

Fatigue fracture failure analysis of 12Cr12Mo steam turbine blade

Turbine blade is one of the key components in thermal power plant, and its premature failure is a common accident. The fourth blade of the low-pressure turbine unit in a power plant broke, resulting in the unplanned shutdown of the turbine unit. Through different analysis methods, the failure cause of the steam turbine blade was determined. The macro morphology of the fracture was observed by optical light microscope (OLM), and the micro characteristics of the fracture were observed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The mechanical properties of the failed blade were analyzed by room temperature tensile test and Charpy impact test. The results indicated that the root cause of blade fracture was the decrease of fatigue strength and rupture strength caused by high δ-ferrite content. Consistency between crack propagation direction and banded δ-ferrite direction further promotes crack initiation and prolongation. Eventually leading to fatigue fracture of the blade. According to the test and analysis results, some recommendations to prevent the early failure of steam turbine blades are put forward.

Vibration analysis and parametric identification of low-pressure steam turbine blade with crack using ANN

Vibration analysis and parametric identification of low-pressure steam turbine blade with crack using ANN

Last stage stator blade profile improvement for a steam turbine under a non-equilibrium condensation condition: A CFD and cost-saving approach

Non-equilibrium phenomena and related damages have always been one of the great concerns among researchers, designers, and industry managers. In power plants, the overhaul of turbines during a pre-planned schedule includes checking, repairing, and replacing damaged parts, which always challenge industry investors with variable costs. In this study, a modified profile for the stationary cascade blades of a 200 MW steam turbine is predicted by help of the Computational Fluid Dynamics (CFD) according to a cost-saving approach for a power plant. Wet steam model is used to investigate the flow behavior between the turbine blades, due to the sonication and non-equilibrium phenomena. The numerical model based on the Eulerian-Eulerian approach accounts the turbulence caused by the presence of droplets, condensation shocks and aerodynamics. At first, such model has been carefully validated against the available experimental data. Then, the entrance edge of the blade is designed considering different shapes and sizes. The flow behavior at the entrance edge region has been fully investigated. Finally, according to the criteria for measuring the non-equilibrium flow phenomena (erosion rate, Mach number, entropy, exergy destruction and transfer of mass and heat between flow phases), a modified model for the steam turbine blade considering the economic aspects has been presented. The modified blade model exhibits 88%, 0.13% and 7% reduction in the erosion rate, entropy generation and exergy destruction, respectively. Furthermore, the application of this modified blade profile save 456$ of the total monthly maintenance costs.

Aeroelastic Characteristics of Rotor Blades of Last Stage of a Powerful Steam Turbine

Blades of powerful steam turbines are subjected to significant unsteady loads, which, in some cases, can lead to the appearance of self-excited oscillations or auto-oscillations. These fluctuations are extremely dangerous and negatively affect the life time of the blading. When developing new or upgrading existing turbine stages, it is necessary to carry out research on the aeroelastic behavior of the rotor blades. As a result of the modernization of a low-pressure cylinder of a 1000 MW steam turbine, the length of the rotor blades of the last stage increased to 1650 mm. In this regard, a numerical analysis of the aeroelastic characteristics of the last-stage rotor blades in the nominal operation mode was carried out. The analysis used the method of solving the coupled problem of unsteady aerodynamics and elastic blade vibrations, which allows the prediction of the amplitude-frequency spectrum of unsteady loads and blade vibrations in a viscous gas flow. The paper presents the results of numerical analysis of aeroelastic characteristics of the last stage rotor blades both for the mode of controlled harmonic oscillations with a given amplitude and inter-blade phase shift, and for the mode of coupled oscillations of the blades under influence of unsteady aerodynamic forces. The results of the simulation of coupled oscillations of blades for the first five natural forms are presented in the form of the time distribution of displacement of the blade peripheral cross-section, as well as the time distribution of forces and moments acting on the peripheral cross-section. The corresponding amplitude-frequency spectra of displacements and loads in the peripheral section are also given. The results of the calculations showed a positive damping of oscillations, the absence of flutter and auto-oscillations for the first five natural forms of oscillations of the blades in the nominal operation mode of the steam turbine

Predictive Modeling and Analysis of Material Removal Characteristics for Robotic Belt Grinding of Complex Blade

High-performance grinding has been converted from traditional manual grinding to robotic grinding over recent years. Accurate material removal is challenging for workpieces with complex profiles. Over recent years, digital processing of grinding has shown its great potential in the optimization of manufacturing processes and operational efficiency. Thus, quantification of the material removal process is an inevitable trend. This research establishes a three-dimensional model of the grinding workstation and designs the blade back arc grinding trajectory. A prediction model of the blade material removal depth (MRD) is established, based on the Adaptive Neuro-Fuzzy Inference System (ANFIS). Experiments were carried out using the Taguchi method to investigate how certain elements might affect the outcomes. An Analysis of Variance (ANOVA) was used to study the effect of abrasive belt grinding characteristics on blade material removal. The mean absolute percent error (MAPE) of the established ANFIS model, after training and testing, was 3.976%, demonstrating superior performance to the reported findings, which range from 4.373% to 7.960%. ANFIS exhibited superior outcomes, when compared to other prediction models, such as random forest (RF), artificial neural network (ANN), and support vector regression (SVR). This work can provide some sound guidance for high-precision prediction of material removal amounts from surface grinding of steam turbine blades.

Corrosion Fatigue Analysis in Power Steam Turbine Blade

The corrosion fatigue behavior of a martensitic stainless steel AISI 410 with 12% Cr, used in the fabrication of steam turbine blades at low pressure (L-P), was studied using the electrochemical noise technique (EN) under mechanical fatigue (immersion and aired) conditions. The tests were done in a simulated environment using four levels of mechanical stress (Δσ) in a 3 wt.% NaCl solution at 90 °C. The specimens underwent pitting corrosion when exposed to the corrosive environment; afterwards, such pits generated mechanical strength sites over the metallic surface, facilitating the initiation and propagation of cracks, which was already enhanced by the applied cyclic loads. From scanning electron microscope (SEM) images, it was possible to observe localized plastic deformation. In such instances, the fatigue damage was caused by the microplasticity (μ), i.e., the shear strength, resulting from the breakdown of the passive layer that was subjected to mechanical load, which led to a significant increment of the velocity of crack propagation, and therefore, a decrement of the useful life of the material. The obtained results show that the fatigue resistance limit in the corrosive medium was lower than that observed in aerated conditions due to the sum of the effects of mechanical fatigue and corrosion.

Effect of the technological parameters of plasma-arc spraying of flux-cored wire on the structure and properties of intermetallide coatings based on Fe3Al

Existing techniques for applying intermetallide layers are characterized by low productivity, difficulties associated with the maintenance and operation of technological equipment, as well as significant costs for the purchase of materials for spraying. Therefore, modern science shows considerable interest in the development of new, highly effective technologies to form intermetallide coatings on the surface of articles. Such promising techniques include the technology of plasma-arc spraying (PAS) of flux-cored wires. This technique has a number of significant advantages, namely high performance, relative simplicity, as well as the affordability of equipment and materials for coating. This paper reports a study into the structure and properties of coatings obtained by flux-cored wire PAS, in which the steel sheath and aluminum powder filler interact when heated with the exothermic effect of Fe3Al synthesis. The influence of technological parameters of PAS process on the structure and properties of Fe-Al coatings was investigated by means of mathematical planning of the experiment. It was found that in all samples the main phase is an intermetallide of the Fe3Al type. Tests for gas-abrasive wear resistance at room temperature showed that the wear resistance of coatings exceeds the stability of steel S235 by an average of 2 times. As a result of studying the electrochemical properties in a 3-% aqueous solution of NaCl and in a 0.5-% solution of H2SO4, the score of corrosion resistance for these media was determined, which was, respectively, 4 and 5 (coatings belong to the group of "resistant"). In this regard, the practical use of coatings based on the Fe3Al intermetallide is recommended for protection against oxidation, corrosion, and gas-abrasive wear of components and assemblies in the heat power industry (heat exchanger pipes, catalytic converters, steam turbine blades, shut-off valves, etc.)

Frequency and modeshape evaluation of steam turbine blades using the metal magnetic memory method and vibration wave propagation

Identifying frequency and modeshape of vibration to which a given mechanical structure is subjected most of its operational time is a key issue in diagnostics of the technical condition of the machine. By evaluating these modal parameters, the sources of vibration, and thus the possible sources of damage can be identified. The current paper presents a new diagnostic technique based on the metal memory method (MMM), which can be used for identification of operational frequency and modeshape of steam turbine blades. The MMM method includes the measurement and analysis of blade's residual magnetic field (RMF) distribution, which reflects directions of main stresses resulting from working loads. It is demonstrated that based on the results of RMF measurement, vibration frequency and modeshape, to which the blade is subjected most of the time, can be evaluated. To calculate these modal parameters, stress waves propagating along the blade, and the resulting standing wave have been considered. Clear correlation between blade’s magnetic field distribution, stress distribution, and FEM results of frequency and modeshape calculation has been observed. It has been confirmed that the frequency and modeshape at which the blade vibrates during its normal operation is close to the blade's 10th natural frequency, which is about 1014 Hz.

Numerical analysis of hot steam injection through an embedded channel inside a 3D steam turbine blade

The steam expands rapidly and releases its latent heat at the last stages of steam turbines, forming a large number of tiny liquid droplets. This non-adiabatic process results in a sudden phenomenon known as condensation shock, leading to significant thermodynamic losses. Given that the condensation phenomenon can reduce the performance of steam turbines and shorten their lifespan, several studies in recent years have been proposed to eliminate liquid droplets, some focusing on surface heating, others on hot steam injection. However, providing a practical platform design for hot steam injection remains to be studied, which defines the primary goal of this investigation. In this research, a channel is installed inside the 3D turbine blade, allowing hot steam to enter and be stored there. Then, the stored hot steam enters the mainstream flow through eight injection holes with unequal mass flow rates from each hole. Six criteria are defined to see how hot steam injection contributes to decreasing wet steam losses and affects other key parameters. The results of CFD simulations indicate that hot steam injection reduces the rate of erosion, condensation losses, and wetness, respectively, by 58%, 28.5%, and 31.5%. Notwithstanding the advantages of this method, kinetic energy decreases by about 0.5%. This, however, seems to be acceptable due to the remarkable reduction of erosion and condensation losses. Finally, the obtained results indicated the fact that injecting hot steam through the designed channel costs roughly 0.45 ($/hour).

Creation and study of intermetallic coating of the Ni–Ti system reinforced with tungsten carbide to increase wear resistance of titanium alloy

The results of studying the intermetallic coating of the Ni–Ti system with the addition of tungsten carbide are presented. The coating was synthesized on the surface of titanium alloy VT6 using an integrated approach – preliminary deposition of a precursor coating from monometallic nickel by cold gas-dynamic spraying and subsequent laser processing. It is shown that the introduction of tungsten carbide into the intermetallic matrix provides an increase in hardness by a factor of three or more, as well as a decrease in wear intensity by a factor of 80 compared to the wear resistance of VT6 titanium alloy. A technology has been developed and a batch of steam turbine blades with a wear-resistant coating on the surface of shrouds has been manufactured.

Reduction of water droplets effects in steam turbine blade using Multi-objective optimization of hot steam injection

As one of the most important equipment for energy conversion, steam turbine plays an irreplaceable role in industry. Due to the high velocity, the non-equilibrium condensation will take place in the steam turbine, emerging lots of tiny droplets. The tiny drops will not only deteriorate the efficiency but also endanger the safety of the steam turbine. The control of droplets size and liquid mass fraction is essential issue in steam turbine blade. One of the techniques that reduce the effects of the liquid phase on steam turbine blades is to inject hot steam. This study investigates hot steam injection in steam turbine blades for dehumidification by considering friction and thermal entropy generation. First, the injection parameters (injection location, slot width, pressure and temperature) are examined parametrically, and their impacts on the generated friction and thermal entropies, condensation loss, erosion rate, hot steam injection rate, and blade inlet flow rate are investigated. The optimization is carried out by the genetic algorithm. The results show the generated friction and thermal entropies increase through the hot steam injection, which, in an optimum state, can reduce the condensation loss, erosion rate, and blade inlet flow rate by 21%, 89%, and 4.9%, and raise the generated entropy by 22%. Moreover, the rate of the hot steam injection equals 4.3% in this condition.

Characterization and wear properties of plasma sprayed Cr3C2 and Stellite coatings on Inconel 625

Steam turbine blades are subjected to wear because of the continuous exposure to high pressure and temperature of the steam. Excessive wear in the blades adversely affects the power generation. Super alloys are commonly used to overcome these issues. Inconel 625 has been considered for analysis in the current work. To further enhance the wear resistance, Cr3C2 and Stellite were added. The wear behavior of Inconel 625 coated with Cr3C2 and Stellite at constant load and various temperatures are investigated. These coatings were deposited on the base metal by using the atmospheric plasma spray coating process. Fabricated sample pieces are characterized by Energy-dispersive X-ray spectroscopy (EDAX), Scanning Electron Microscope (SEM) and Vicker’s microhardness tester. Pin on disc tribometer has been used to study the friction and wear behaviour of the fabricated samples. Impact of the coatings with respect to wear are investigated with the help of SEM and EDAX. At various temperature settings, wear caused by the sliding of Inconel 625 coated with Cr3C2 and Stellite against the EN-8 steel disc are discussed. Temperature variations has affected both the coating’s removal and elemental composition. Stellite at room temperature and Cr3C2 at 400 °C significantly reduced the wear rate of Inconel 625 subjected to 20 N load condition.

Damage evaluation and life assessment of steam turbine blades

Steam turbines in their last stages, L-0 stage, generate approximately 12% of the total power produced by thermoelectric plants. These steam turbines blades present centrifugal loads and unstable flows by rotating. Both there are the main causes for fatigue crack initiation [1]. As a consequence of this crack initiation, dynamical behavior in blades is altered. These dynamical variations in damping, stiffness, and natural frequencies in presence of cracks are investigated and evaluated to prevent damage and life assessment (useful life) until to failure. Experimental fatigue tests and modal analysis in samples of 410SS, stainless steel were performance to obtain the S-N curve and boundary conditions for the numerical analysis performance in Ansys workbench®. These experimental tests provide some magnitudes to numerical simulation. Numerical modal analysis, random vibrations with power spectral density are performed to detect these changes in damping, stiffness, and natural frequencies in the group of ten blades of the last stage of a 110 MW steam turbine. The Steinberg 3-band technique and Palmgren-Miner cumulative damage rule were used to calculated fatigue damage and useful life. Results show that different crack sizes change the performance of steam turbine blades. If changes in damping, stiffness, and natural frequencies with fractured blades are detected, it is possible to determine these damages and predict useful life. The cumulative damage is obtained with RD = 1.232 and useful life is estimated in the blades group with changes in damping ratio due to cracks in blades with a result of 6.14 min.

Multi-objective optimization of supercooled vapor suction for decreasing the nano-water droplets in the steam turbine blade

Nowadays, decreasing the losses in industrial equipment as well as increasing their lifetime are of special importance. A steam turbine is one of the essential equipment in power plants. Due to the high prices of steam turbines, the issues of loss decrease and maintenance are crucial. One of the remarkable problems in the last stage of the steam turbine is the two-phase flow which leads to efficiency reduction and mechanical damage to the turbine blades. One of the techniques for decreasing the liquid phase in the steam turbines is the drainage groove. The innovation of the present paper is utilizing the drainage groove for supercooled vapor suction. Then, through optimization of the drainage groove, attempts are made to decrease the condensation losses, erosion rate, and the entropy generated in the steam turbine blade. To do this, the multi-objective optimization method of TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) is used. The optimization is done on the variables of the drainage groove (location, angle, width, and the pressure of drainage grooves). Based on the results, the optimized status is as follows: location 3, angle 90, width 0.06, and drainage pressure 80 kPa. In this status, condensation loss and erosion rate decreased by 5% and 62%, respectively, the entropy generated increases up to 1.03%, and the liquid drainage ratio and total drainage ratio are 3.22% and 3.8%.

Fatigue life prediction of turbine blades with geometric imperfections made of stainless steel

This research addresses critical challenges faced by steam turbine blades, particularly in low-pressure (LP) turbines, where premature failures are common due to stress concentrations at the blade root area. The study introduces a numerical methodology aimed at predicting the life of mistuned steam turbine blades, with a focus on variations in blade geometry which have received limited exploration in existing literature. A simplified, scaled-down mistuned steam turbine bladed disc model was developed using Abaqus finite element software. Acquisition of steady-state stress response of the disc models was performed through finite element analysis (FEA). Thereafter, numerical stress distributions were obtained. Subsequently, within Companion software, a Monte Carlo simulation-based probabilistic approach was applied to evaluate and quantify uncertainties in fatigue life for 17 cases. This analysis considered an accepted manufacturing percentage scatter of ± 5 % for the steam turbine bladed disc. That was conducted by selecting mistuning (geometry variation) percentages as the random variables. The methodology demonstrated reliability, correlating well with literature-based and discrete fatigue life results. This study establishes the potential for accurately predicting the fatigue life of mistuned steam turbine blades using the developed methodology.

INVESTIGATING THE EFFECTS OF OUTLET PRESSURE FROM STEAM TURBINE BLADE ON WETNESS AND ENTROPY GENERATION WITH CONSIDERATION OF NON-EQUILIBRIUM CONDENSATION

Steam turbines are one of the main elements of a power plant that steam thermal energy turns into rotational energy. Due to condenser pressure changes, the pressure at the end of steam turbines changes. In this study, the Bakhtar blade is used, and the effects of changes in the pressure outlet of the blade on the flow behavior are investigated. In this research, 62.56 kPa, 72.56 kPa, 82.56 kPa, 92.56 kPa, and 102.56 kPa are considered for the pressure at the end of the steam turbine blade. First, the CFD solution results are compared with the laboratory data of the Bakhtar turbine's blade. Then, the effect of outlet pressure is examined. Regarding obtained results, the proposed numerical solution can properly predict the experimental data. By the growth of the outlet pressure of the steam turbine blade, the Mach number decreases and the pressure and temperature distribution increase. As the pressure increases from 62.56 kPa to 102.56 kPa, the average Mach number decreases by 29.8% at the outlet, and the average temperature at the outlet increases by 3.9%. The nucleation rate does not have a noticeable change. However, liquid mass fraction decreases with the increase in outlet pressure. By increasing the pressure from 62.56 kPa to 102.56 kPa, the average wetness decreases by 39.5% at the outlet. This study shows that condenser pressure changes affect the liquid phase produced in the end blade of the steam turbine.

Structural and thermal analysis on high-pressure steam turbine blade to determine the optimum material for its manufacturing

Blades of turbines are key elements of steam turbines. They are the main energy driven components at every stage of steam turbine where steam is pressurized to generate power. In view of designing, the material used and dimensions of blade govern the efficiency, consistency and durability of a steam turbine. In this paper the design of aerofoil profile of HP steam turbine blade is modelled by using computer-aided three-dimensional interactive application (CATIA). Various analytical data viz.., static structural analysis, transient structural analysis and transient thermal analysis are performed on different materials (ATI 720, Waspaloy, Molybdenum TZM, Incoloy alloy, Inconel alloy 725). Based on the analysis, Waspaloy material blade outperformed among all blades materials in terms of creep resistance and heat flux.

Evaluation of X22CrMoV12-1 Alloy with Vanadium Carbide Addition Submitted to Powder Metallurgy

Usually, scraps of X22CrMoV12-1 alloy are obtained through machining of steam turbine blades and recycled through casting. However, this process is considered too costly. The viability of recycling X22CrMoV12-1 scraps with addition of vanadium carbide (VC) through powder metallurgy was analyzed in this study. Scraps of X22CrMoV12-1 alloy with VC were milled in a planetary ball mill during 10, 30 and 60 hours. The granulometry of the powder was determined through laser granulometry. The evolution in particles morphology and amorphization was conducted using scanning electron microscope (SEM) and x-ray diffraction (DRX) techniques. Stress-strain curves were obtained through compressive strength test. The results indicated that the best milling condition found was 60 hours. Also, the X22CrMoV12-1 alloy with VC addition produced by powder metallurgy showed good mechanical strength. Thus, this route was considered promising to reshape this material with smaller energy involved in the process.