Failure analysis of a gas turbine blade made of Inconel 738LC alloy

Newly revised, this new fifth edition includes a chapter on waste heat recovery and discusses this technology in detail including a the advantages and barriers to waste heat recovery, environmental restraints, thermodynamics of heat recovery, fluid properties, boiler, condensers, steam turbines, off design behavior and exhaust catalyst. This book shows how microturbine designs rely heavily on the centrifugal compressor and are, in many aspects, similar to the early flight engines and will illustrate how the approach of the microturbine designer is to minimize cost.

Gas Turbine Handbook: Principles and Practices

such cases might at times give rise to ambiguity, but in my data the intended meanings of such occurrences could be ferreted out with the help of the context. 55 As Greenbaum (1969: e.g. 174 ff.) illustrates, there are also adverbs that can be placed into more than one of the syntactically determined categories (e.g. rarely as an adjunct and a disjunct). However, it seems that there is not much of a difference in the meaning of such items even though they might at times behave differently in syntactic terms. 56 Many of the items in the four subcategories established are included in what Biber et al. (1999: 557 ff.) describe as “epistemic stance adverbs”—a notion which could in fact serve as a cover term for the four types of adverb distinguished. 57 As noted above, in terms of hedging potential, the syntactic status of the adverbs is of secondary interest, but syntactic considerations may come in handy in dealing with certain problematic cases. 58 The 13 items are: apparently, arguably, likely, perhaps, possibly, potentially, presumably, probably, seemingly, supposedly, tentatively, theoretically, unlikely. 59 Naturally, some of the adverbs treated here may also be used when for instance describing precise figures presented in a table or the like, especially when providing comparisons of figures obtained (e.g. x occurred more frequently than y). Cases where adverbs are used in descriptions of precise figures cannot obviously be taken to constitute hedging. 60 It would be interesting to determine the precise motivation underlying the various instances of hedging found in the corpus in the form of expressions of indefinite frequency and the like. However, although such a project could in principle be carried out by obtaining information as to the use of each and every device of this kind from the authors of the articles scrutinized, this would apparently constitute an arduous undertaking indeed given the frequency of such devices. 61 The 11 items identified are commonly, frequently, generally, normally, occasionally, often, rarely, seldom, sometimes, typically, and usually. 62 The terminology applied to refer to adverbs is quite varied, Hyland (1998: 139) for instance describing as adjuncts the same kinds of item included in Quirk et al.’s subjuncts occurring as expression diminishers. 63 The terminology relating to adverbs of this kind and other devices with similar meanings is varied and may sometimes even be somewhat confusing. While Salager-Meyer (1994) uses the term approximator to refer to a variety of expressions involving a number of different word classes—including indefinite indications of quantity, degree, frequency, and time—the same term is elsewhere (Quirk et al. 1985, Hyland 1998) employed in a much more restricted sense to refer to a relatively narrow range of adverbs such as almost and virtually. 64 The adverb significantly cannot be seen as a hedge in all contexts. Particularly in RAs it is commonly used when discussing statistics-based probabilities, as in Educational attainment significantly altered the risk of having an infarction triggered by an outburst of anger. Figure 1 shows that the RR of MI onset decreased consistently with increasing educational attainment (P=.03) [...]. (MED1, G, “Results”, paragraph 3 [Results]) In such instances, the adverb is in fact used with reference to specific predetermined limits as concerns statistical probability values, the adverb indicating that the results obtained conform to the limits of what may be seen as a statistically significant result. Occurrences of this kind were not counted as instances of hedging. 65 The items distinguished are: considerably, dramatically, drastically, fairly, greatly, highly, largely, mainly, markedly, moderately, modestly, mostly, partly/partially, predominantly/predominately, primarily, principally, quite, rather, reasonably, relatively, significantly, slightly, somewhat, strongly, substantially, widely. 66 The hedge in the last example, somewhat, is an interesting case where hedges are embedded within a hedge of another kind. While the entire beginning of the example might be taken as a hedge by which the authors draw attention to the limitations of their study and thus indicate that it may not be categorically correct in every sense, the adverb (as well as the auxiliary may) included in the caveat appears to tone down the negative effect involved. If the hedges toning down the caveat were omitted, the effect of the caveat would be much stronger, undermining the authors’ work to a much more considerable extent. The use of somewhat (and may), however, is a useful means of indicating that the limitations are not very grave, the indeterminacy of the hedge allowing the authors to be safely vague about the putative limitations of their research. 67 The items identified are: about, almost, approximately, around, closely, essentially, just, nearly, roughly, some, virtually. 68 In view of word-formational characteristics, it would seem more reasonable to deal with adjectives prior to discussing adverbs, many of the latter being formed from adjectives. However, as concerns the present corpus,

Hedging in Scientifically Oriented Discourse. Exploring Variation According to Discipline and Intended Audience

Coupled effects of temperature gradient and oxidation on thermal stress in thermal barrier coating system

A continuum crystal plasticity model is used to simulate the material behavior of a directionally solidified Ni-base superalloy, DS GTD-111, in the longitudinal and transverse orientations Isothermal uniaxial fatigue tests with hold times and creep tests are conducted at temperatures ranging from room temperature (RT) to 1038°C to characterize the deformation response The constitutive model is implemented as a User MATe-rial subroutine (UMAT) in ABAQUS (2003, Hibbitt, Karlsson, and Sorensen, Inc, Providence, RI, v63) and a parameter estimation scheme is developed to obtain the material constants Both in-phase and out-of-phase thermo-mechanical fatigue tests are conducted A physically based model is developed for correlating crack initiation life based on the experimental life data and predictions are made using the crack initiation model

Thermomechanical Fatigue Behavior of a Directionally Solidified Ni-Base Superalloy

Prediction of Thermal-Mechanical Fatigue Life for Gas Turbine Blades in Electric Power Generation

The rotor exhaust gas bulk total temperature relative to the last blade row of a combustion turbine is determined by traversing an optical pyrometer radially across the last stage blades. The resulting radial temperature measurements are then flow weight averaged to provide an accurate bulk gas temperature relative to the last row of blades. Such temperature is useful in a feedback control system for the turbine. A technique of traversing is to cause the optical pyrometer to traverse by mounting its line of sight or optical axis at an angle to its axis of rotation.

Apparatus for measuring rotor exhaust gas bulk temperature in a combustion turbine and method therefor

Results from an analysis of cracked first stage blades (or buckets) from two General Electric Frame 7001 E industrial/electric utility gas turbines are presented. Numerous cracks were observed along the leading-edge and mid-chord regions of the pressure and suction surfaces. In one unit cracks were found after 874 start-stop cycles, which included 218 trips from load and 11,000 service hours. Buckets in the sister engine were examined after 1800 cycles, which included 218 trips from load and 24,000 service hours. In both cases, cracks initiated in the platinum aluminide coating and propagated into the IN-738LC base metal. For the 11,000-hour bucket, 20-mil (0.5-mm) deep cracks were observed, and for the 24,000-hour bucket, the leading edge cracks had grown to the leading edge cooling hole, a distance of 0.2 inches (5 mm). The number of cycles to crack initiation was in good agreement with thermal mechanical fatigue (TMF) predictions from the REMLIF computer program, which is part of the Electric Power Research Institute's (EPRI) Life Management System. The cracking was greatly accelerated by the large number of trips experienced. The extensive crack propagation that occurred is thought to have been strongly assisted by oxygen and sulfur penetration along the grain boundaries. The coating on the leading edge degraded from the original platinum-aluminide plus beta phases to a gamma prime phase after 24,000 hours of service, but it was still protective except where it was cracked. Where the coating was cracked, environmental attack of the interdiffusion zone and base metal occurred, resulting in spallation of the coating and preferential grain boundary attack. Operating and maintenance considerations for optimizing bucket life in demanding cyclic duty environments are also discussed.

Analysis of Cracked Gas Turbine Blades

Analyses of first-stage nozzle cracking in General Electric Model 7001B and 7001E industrial gas turbines are presented. Empirical algorithms are developed to predict the maximum extent of cracking that is visible on these nozzles as a function of engine cyclic history and the number of fired hours. It is shown that the algorithms predict this cracking to within a factor of two. Metallurgical analyses of nozzles show that crack growth follows the carbide-matrix interface, environmental attack occurs at the crack tip, and that the microstructure changes by increasing the amount of carbide precipitation, which increases the hardness. These metallurgical results, along with mechanical test data and stress analyses from the literature, are used to understand the nature of nozzle cracking. The maximum extent of cracking coincides with locations of maximum thermal stresses as determined by finite element analyses of similar nozzle designs. This location is at the airfoil-shroud junction on the middle vanes of multivane castings. The use of these algorithms as a predictive maintenance tool and the ability to inspect nozzles visually in the engine also are discussed.

Analysis of General Electric Model 7001 First-Stage Nozzle Cracking

/pdf/analysis-of-cracked-gas-turbine-blades-vsz9bu308h.pdf

James M. Allen

Papers

Prediction of Thermal-Mechanical Fatigue Life for Gas Turbine Blades in Electric Power Generation

Apparatus for measuring rotor exhaust gas bulk temperature in a combustion turbine and method therefor

Analysis of Cracked Gas Turbine Blades

Analysis of General Electric Model 7001 First-Stage Nozzle Cracking

Analysis of Cracked Gas Turbine Blades