Industrial Gas Turbine Blades Research Articles

Gas turbine blade fracturing fault diagnosis based on broadband casing vibration

Blade fault is a catastrophic failure of gas turbines. In order to improve the reliability of blade during operation, condition monitoring is one of the effective methods. However, there always exist two problems with blade monitoring: 1) challenges in warning of the occurrence of blade failure in advance and 2) difficulties finding the location after blade failure. In this article, we solve these problems by excavating the characteristics of blade-related signals in broadband casing vibration with advanced signal processing methods and machine learning technology. First, a novel method--Sparse Harmonic Product Spectrum (SHPS)--is proposed to accurately calculate blade passing frequency from gas turbine broadband casing vibration. The SPHS relies on Fourier transform, and its calculation utilizes the physical relationship between fundamental frequency and blade passing frequencies. Combining Vold-Kalman filter with adaptive parameter optimization process (AVKF), the blade-related vibration can be separated from casing vibration even in strong noise. Analysis of simulated casing vibration signal is used to verify the effectiveness and superiority of proposed method. Based on blade-related vibration, we build a gas turbine blade condition model in an unsupervised learning manner. The model can excavate potential blade failures earlier and more accurately than conventional threshold methods. Then, three coefficients are constructed according to the blade-related vibration characteristics to identify the blade fault location in multi-stage system. Moreover, the effectiveness of the proposed blade diagnosis framework is verified using actual industrial gas turbine blade fracturing failure data.

Creation of a Life Prediction Model for Combined High-Cycle Fatigue and Creep

Abstract While industrial gas turbine blades are commonly designed to resist creep and high-cycle fatigue (HCF) failure, the combination of these two loading conditions is seldom considered. The effect of creep damage elicited prior or concurrent to HCF loading is not well established and can significantly reduce the HCF lifetime of these critical components. A comprehensive life prediction model capable of capturing these superimposed effects is needed to ensure current reliability standards are maintained when designing aggressively loaded, next-generation industrial gas turbine blades. The consequence of combined HCF and creep loading to the lifetime a Ni-base superalloy is characterized and modeled in this study. Composition and calibration of the model are carried out using data from HCF tests conducted on virgin and pre-crept specimens at 750 °C and 850 °C. The experimental data encompass a wide range of stress ratios and pre-creep strains to mimic to the expansive set of potential turbine blade loading conditions. The proposed microstructurally informed model is based on existing principles and relies on test data and information gathered from a comprehensive failure analysis of the tested samples.

Data‐Driven “Cross‐Component” Design and Optimization of γ′‐Strengthened Co‐Based Superalloys

The design of complex multicomponent superalloys has always been challenging due to the interaction of multiple elements and stringent requirements for various properties. Herein, an integrated approach to designing the high‐component (>7) γ′‐strengthened Co‐based superalloys with well‐balanced properties is developed by combining the diffusion multiples and machine‐learning models. A “cross‐component” prediction is achieved by the machine‐learning models, where two types of novenary superalloys are screened out for aeroengine and industrial gas turbine blades, respectively, based on the experimental database mainly consisting of six to seven elements. The method is verified to be effective or slightly more favorable than the Calculation of Phase Diagram (CALPHAD) in predicting the γ′ solvus temperature (Tγ′) and phase constituent of the high‐component alloys when reasonable data of low‐component alloys are just provided. Furthermore, the oxidation resistance and hardness of polycrystal superalloys as well as the compressive strength of single‐crystal superalloys are tested. Finally, some factors affecting the accuracy of “cross‐component” prediction are discussed. Expanding the compositional range and supplementing the critical interaction data of multiple elements in the database are beneficial for improving the accuracy of the “cross‐component” prediction.

Duration-affected creep behaviors of Ni-based single crystal superalloys with/without rhenium addition designed for IGT application

In this study, the creep behaviors of two Ni-based single crystal superalloys with/without Re addition designed for industrial gas turbine application were investigated at 900 °C under a range of applied stresses (200 MPa–330 MPa), and the examinations of the microstructures and dislocation configurations were performed at the minimum creep rate and creep rupture under each condition of both alloys. The results indicated that although the creep lives spanned over thousands of hours under different stresses, dislocations underwent the similar mechanisms including the proliferation and movements by gliding-climbing process in decelerating stage, followed by the progressive increase in dislocations shearing into the γ′ phases until creep rupture in each alloy. This led to a special rafting regime which was characterized by the sluggish formation of the rafting structure in the present superalloy, considering the relatively lower γ′ volume fraction, lower lattice misfit, and lower elemental diffusion of the experimental superalloys than those of traditional Ni-based superalloys. Thus, the “duration effect” was proposed to describe the strong correlation between the creep duration and microstructural evolution, which showed insensitivity to the applied stress and accumulation strain, resulting in the consistently exponential relationships between the time to the minimum creep rate and the applied stress or creep life of each alloy within a wide range of stresses. The addition of Re gave rise to an inversion of the rafting tendency during high-temperature creep without changing the deformation mechanism under different stresses. Nevertheless, the addition of Re could still enhance the creep property under each stress, which contributes to provide insights for optimizing the alloying design and enhancing long-term reliable service of industrial gas turbine blades.

Unveiling the Re effect on long-term coarsening behaviors of γ′ precipitates in Ni-based single crystal superalloys

In response to the increased demand for very long-term service reliability of industrial gas turbine (IGT) blades, the microstructural stability of two single crystal (SX) superalloys with different Re addition (0Re and 2Re in wt.%, named as alloy 0Re5Ta and 2Re5Ta) were investigated during long-term thermal exposure (>5000 h) at 900 °C, with the help of atom probe tomography (APT) and high-temperature X-ray diffraction (XRD) analysis. During long-term thermal exposure, the γ′ precipitates coarsened gradually in both alloys. At the same time, the γ′ precipitates became more cuboidal for alloy 0Re5Ta and nearly spherical for alloy 2Re5Ta due to the increased positive lattice misfit for alloy 0Re5Ta and the decreased negative lattice misfit for alloy 2Re5Ta. Such lattice misfit evolution was mainly attributed to the inversion of the W partitioning from γ matrix to γ′ precipitates over time. The addition of Re can effectively decrease the coarsening rate during thermal exposure. Further investigations on the coarsening kinetics confirmed the Re effect on reducing the interfacial energy and enhancing the rate-limiting effect of Cr. Additional particle size distributions (PSDs) showed a gradual transition from the initial matrix-diffusion coarsening-controlled mechanism to the interface-diffusion coarsening-controlled mechanism at prolonged time, wherein Re triggered the interface-diffusion mechanism earlier by leading to sharper interfaces. Although Re increases the magnitude of the lattice misfit in the initial microstructure, it can significantly enhance the microstructural stability of SX superalloys for IGT application.

Intermediate temperature creep damage mechanisms of a directionally solidified Ni-based superalloy

ABSTRACT Microstructure evolution and damage mechanisms during the creep deformation of a directionally solidified Ni-based superalloy were evaluated. The creep deformation behaviour was studied along the longitudinal direction (i.e. along the solidification direction), at a moderate temperature of 870 °C, and applied stresses ranging from 310 to 450 MPa concerning the service conditions in industrial gas turbine blades. It was shown that at the lower stress levels of about 310 MPa, the average creep strain rate decreased by two orders of magnitude, while tertiary creep appeared as the dominant stage. Progressive coarsening of γ’ precipitates was also observed, meantime γ’ precipitate shearing was confirmed to occur over the evaluated range of stresses.

Comparison and selection of suitable materials applicable for gas turbine blades

In the aircraft engine, marine engine and power generation field gas turbine has wide applications. The innovation of material for gas turbine is always required because, higher the capability of the material to withstand elevated temperature, the more will be the efficiency of the engine. In this new era of technology, demand for increasing the parameter of the industrial gas turbine is growing very fast, hence the efficiency must increase. This leads the manufacturers all over the world to develop new technology, new material, and a new method of manufacturing to increase the efficiency of the industrial gas turbine. Among these, the material plays a vital role, hence it should be as such they can withstand the extreme conditions and give maximum efficiency. It is observed that 42% of failure in the gas turbine is due to the failure of turbine blades, therefore, it is an important component to be taken care of. Turbine material selection plays a vital role. In this work, materials applicable for industrial gas turbine blades are reviewed with the focus on the material properties required and comparative analysis is done to select the suitable material. The materials are reviewed based on the methods of casting. Different Superalloys with typical compositions are analysed for tensile properties at different temperatures and their chemical composition analysis is also done. With this analysis of mechanical properties of material at different temperatures and chemical composition, it is observed that alloys like Mar M247, CM 247 LC, CMSX 2 and PWA 1484 are suitable for the gas turbine blade of future generation.

Application of evolutionary algorithms to optimize cooling channels

The design and development is a complex, repetitive, and more often difficult task, as design tasks comprising of restraining and conflicting relationships among design variables with more than one design objectives. Conventional methods for solving more than one objective optimization problems is to build one composite function by scalarizing the multiple objective functions into a single objective function with one solution. But, the disadvantages of conventional methods inspired scientists and engineers to look for different methods that result in more than one design solutions, also known as Pareto optimal solutions instead of one single solution. Furthermore, these methods not only involved in the optimization of more than one objectives concurrently but also optimize the objectives which are conflicting in nature, where optimizing one or more objective affects the outcome of other objectives negatively. This study demonstrates a nature-based and bio-inspired evolutionary simulation method that addresses the disadvantages of current methods in the application of design optimization. As an example, in this research, we chose to optimize the periodic segment of the cooling passage of an industrial gas turbine blade comprising of ribs (also known as turbulators) to enhance the cooling effectiveness. The outlined design optimization method provides a set of tradeoff designs to pick from depending on designer requirements.

The synthesis of NiCrAlHf powders with mechanical alloying method for thermal sprayed coating

NiCrAl is a material commonly used for coating in order to increase corrosion or oxidation resistance of materials applied at high temperatures. The addition of hafnium (Hf) as reactive elements to NiCrAl coating are found to prolong the life of the industrial gas turbine blade and increase its performance. NiCrAlHf powders used as the base material were mixed using planetary mill device for 36 hours with a speed of 25 Hz or 1500 rpm. Characterization of NiCrAlHf powder was investigated before and after milling process using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). The results showed that the synthesized powders were agglomerated. The obtained particle size of 9.64 µm, 19.97 µm, 39.27 µm, 19.93 µm, and 22.8 µm was observed before milling process, after 9, 18, 27, and 36 hours milling process, resepectively. The phase formed on the synthesized NiCrAlHf powder after 36 hours milling process included Ni and Cr with crystallite size of Ni 25.4 nm and Cr 8.8 nm calculated by Scherrer method. In addition the peak profile of the Al phase gets more amorphous after 27 hours.

Multiscale Modeling and Simulation of Directional Solidification Process of Ni-Based Superalloy Turbine Blade Casting

Ni-based superalloy turbine blades have become indispensable structural parts in modern gas engines. An understanding of the solidification behavior and microstructure formation in directional solidified turbine blades is necessary for improving their high-temperature performance. The multiscale simulation model was developed to simulate the directional solidification process of superalloy turbine blades. The 3D cellular automaton-finite difference (CA-FD) method was used to calculate heat transfer and grain growth on the macroscopic scale, while the phase-field method was developed to simulate dendrite growth on the microscopic scale. Firstly, the evolution of temperature field of an aero-engine blade and a large industrial gas turbine blade was studied under high-rate solidification (HRS) and liquid-metal cooling (LMC) solidification processes. The varying withdrawal velocity was applied to change the curved mushy zone to a flat shape. Secondly, the grain growth in the aero-engine blade was simulated, and the grain structures in the starter block part and the spiral selector part in the HRS process were compared with those in the LMC process. The simulated grain structures were generally in agreement with experimental results. Finally, the dendrite growth in the typical HRS and LMC solidification process was investigated and the simulation results were compared with the experimental results in terms of dendrite morphology and primary dendritic spacing.

Prediction of freckle formation in directionally solidified CMSX-4 superalloy

Freckle defects appearing on the industrial gas turbine blade reduce the high temperature mechanical properties. It is necessary to predict the freckle formation on the castings before the directional solidification. In this paper, the relationship of fluid flow and crystal growth during the vertical directional solidification was analysed. Based on the analysis, a simple method considering the solidification conditions and concaved solidification interface was proposed to predict the freckle formation. The method was verified with specimens and dummy blade under the experimental environments. The validation results show that the method can predict where the freckle may appear on a casting with a large size and complex shape for directionally solidified CMSX-4 superalloy.

Creep-Fatigue Interaction Life Consumption of Industrial Gas Turbine Blades

This paper presents the creep-fatigue interaction life consumption of industrial gas turbine blades using the LM2500+ engine operated at Pulrose Power station, Isle of Mann as a case study. The linear damage summation approach where creep damage and fatigue damage are combined was used for the creep-fatigue interaction life consumption of the target blades. The creep damage was modelled with the Larson-Miller parameter method while fatigue damage was assessed with the modified universal slopes method and the damage due to creep-fatigue interaction was obtained from the respective life fractions. Because of the difficulty in predicting the life of engine components accurately, relative life consumption analysis was carried out in the work using the concept of creep-fatigue interaction factor which is the ratio of the creep-fatigue interaction life obtained from any condition of engine operation to a reference creep-fatigue interaction life. The developed creep-fatigue interaction life consumption analysis procedure was applied to 8 most of real engine operation. It was observed that the contribution of creep to creep-fatigue interaction life consumption is greater than that of fatigue at all ambient temperatures. The fatigue contribution is greater at lower ambient temperatures as against higher ambient temperatures. For the case study, the overall equivalent creep-fatigue factor obtained was 1.5 which indicates safe engine operation compared to the reference condition. The developed life analysis algorithm could be applied to other engines and could serve as useful tool in engine life monitoring by engine operators.

Effects of Ambient Temperature and Shaft Power Variations on Creep Life Consumption of Industrial Gas Turbine Blades

The effects of ambient temperature and shaft power variations on creep life consumption of compressor turbine blades of LM2500+ industrial gas turbine engine are investigated in this work. An engine model was created in PYTHIA (Cranfield University’s gas turbine software) for the analysis. Blade thermal and stress models were developed and used together with Larson-Miller Parameter method for life analysis. Mean life reduction index, which is the propensity of a given effect to reduce engine life by half, is developed for each effect and applied in this research to compare the impacts of the different effects on the blade creep life. It was observed that blade life will be halved when ambient temperature is increased by 8.11 units while 13.64% increase in shaft power reduces blade life by a factor of 2. The results of this work will guide engine operators in making decisions concerning operating at part loads.

Novel casting processes for single-crystal turbine blades of superalloys

This paper presents a brief review of the current casting techniques for single-crystal (SC) blades, as well as an analysis of the solidification process in complex turbine blades. A series of novel casting methods based on the Bridgman process were presented to illustrate the development in the production of SC blades from superalloys. The grain continuator and the heat conductor techniques were developed to remove geometry-related grain defects. In these techniques, the heat barrier that hinders lateral SC growth from the blade airfoil into the extremities of the platform is minimized. The parallel heating and cooling system was developed to achieve symmetric thermal conditions for SC solidification in blade clusters, thus considerably decreasing the negative shadow effect and its related defects in the current Bridgman process. The dipping and heaving technique, in which thinshell molds are utilized, was developed to enable the establishment of a high temperature gradient for SC growth and the freckle-free solidification of superalloy castings. Moreover, by applying the targeted cooling and heating technique, a novel concept for the three-dimensional and precise control of SC growth, a proper thermal arrangement may be dynamically established for the microscopic control of SC growth in the critical areas of large industrial gas turbine blades.

Risk-based material selection process supported on information theory: A case study on industrial gas turbine

Gas turbine blades are produced using high-temperature high-strength materials because they are often exposed to severe environments. Material selection for such cases should be performed with sensitivity and using a systematic method. Moreover, various risks may exist about the values of materials properties. For example, the difference between the designed and unexpected conditions may pose some risks to materials properties. Although considering risks for gas turbine blade material selection problem or similar high-tech practical cases is important, a research gap exists in such fields. This paper presents a risk-based material selection algorithm using the principles of Suh and Shannon entropies supported on information theory. In this regard, we develop the risk-based fuzzy axiomatic design approach with the integrated Shannon significance coefficients of attributes. A real-world example about material selection of industrial gas turbine blade is examined using four techniques including the fuzzy axiomatic design, weighted fuzzy axiomatic design, risk-based fuzzy axiomatic design, and weighted risk-based fuzzy axiomatic design approaches. In the example, risk factors are determined to consider the effect of temperature variation on materials properties. Finally, the resultant rankings are compared by calculating Spearman rank correlation coefficients. The comparisons show that considering risk factors in the problem affects the resultant ranking. We validate the results of the proposed methods by the unweighted and weighted fuzzy MULTIMOORA approaches.

Small-scale specimen testing for fatigue life assessment of service-exposed industrial gas turbine blades

Service-exposed industrial gas turbine blades made from conventionally cast nickel-base superalloy IN738 were investigated in order to study the effect of service-induced microstructural changes on the tensile and cyclic material properties. Optical microscopy and scanning electron microscopy were used for the microstructural characterization of the gas turbine blades. The microstructural examinations showed a degraded microstructure in the airfoil section, such as γ′ coarsening, MC carbide decomposition as well as M23C6 carbide formation. Uniaxial tensile and isothermal low cycle fatigue tests were carried out at 850°C using small-scale specimens manufactured from the blade root and airfoil section. The service-induced microstructural changes in the airfoil section yielded to a reduction of the tensile properties. Furthermore, a lower fatigue life of airfoil specimens compared to the blade root specimens was observed. Based on the determined fatigue data the residual fatigue life of the gas turbine blades was estimated. Finally, the fatigue crack paths were studied by optical microscopy.

Four Hot Corrosion Resistant Materials for IGT Blades

Four hot corrosion resistance alloys, K444, K435, K452, GH4413, were used for IGT blades. This paper described those four alloys for Industrial Gas Turbine (IGT) blades with the chemical composition, hot corrosion resistant properties and long term structure stability. According to the practical manufacture experiences, the eutectic problem of K444 alloy and the effect of solution temperature on the properties of GH4413 were also studied.

Advanced nanocomposites for high temperature aero-engine/turbine components

This paper provides a report on the research and development work contributing to the co-deposition technique used in the production of nanocomposite coatings by embedding sub-micron (nano-sized) particles into a nanometal matrix by electrodeposition. Electrolytic co-deposition is a technique used to produce composites by embedding small and large particles into the metal matrix during plating; this allows co-deposition of particles with improved properties and is extremely cost-effective. The resistance of a coating to high temperature oxidation and corrosion depends on its structure and composition; also on its interaction with the metal matrix and the corrosion environment. The nanoparticles are expected to pin the grain boundaries and prevent grain growth at high temperatures, e.g., 1,400°C for Ni turbine blades. The electrolytic composites were characterised using SEM. Industrial gas turbine blade (aerospace) has been successfully coated with these nanocomposites as overlay coatings. The focus of this study is primarily in the application of nanocomposites in industrial turbines/aero-engine components and power generation industry. The current state of knowledge of nanocomposite production is presented.

Numerical Modelling of Diffusion Coupled with Cyclic Oxidation. Application to Alumina-Forming Coatings Used for Industrial Gas Turbine Blades

A model using a finite elements code is developed to simulate degradation due to combined cyclic oxidation and interdiffusion in materials used in high temperature components of gas turbines. Coating recession due to cyclic oxidation (oxide growth and spalling) is also modelled using a statistical approach. Interdiffusion between coating and superallloy is modelled to predict total Al depletion in the coating. The phase transformations in the alumina-forming coating and the effects of the precipitates at the coating / superalloy interface are investigated. The results of simulations are compared with experimental data. Effects of diffusion parameters and of cyclic oxidation kinetics are discussed.

A Comparison of Aging Kinetics of New and Rejuvenated Conventionally Cast GTD-111 Gas Turbine Blades

Two industrial gas turbine blades made from a conventionally cast Ni-base superalloy GTD-111, one new and the other rejuvenated, were removed from the same machine after a particular operational cycle for an examination in order to determine the effect of rejuvenation on the material’s behavior during service. It was found that service-induced changes in the microstructure, such as γ′-phase coarsening and coalescence, excessive grain-boundary secondary M23C6 carbides formation, and primary MC carbides decomposition, were noticeably more advanced in the rejuvenated blade. The stress-rupture life of the rejuvenated blade decreased significantly compared to that of the new blade after the same number of hours in service. The cause of this decrease appears to be related to a release of additional amounts of carbon and carbide-forming elements into the matrix during rejuvenating heat treatment as a result of the primary MC carbide decomposition.