Artur Kułaszka

New Non-Destructive Methods of Diagnosing Health of Gas Turbine Blades

The illuminated blade/vane surface can be recognized by a light-sensitive detector (a CCD matrix with an optical system – an optoelectronic device) owing to the fact that the surface becomes a secondary source of light (Zhang et al., 2004; Rafalowski, 2004; Tracton, 2006, 2007). Therefore, it is possible to diagnose the examined object in an indirect way by the processing and analysis of information acquired as digital images (Bogdan; 2008; Blachnio & Bogdan, 2010). Only a very tiny portion of an incident light beam is absorbed by metallic surfaces. Most of the light (90-95%) is reemitted from the reflecting surface as visible light with the same wavelength as the incident light. The remaining 5-10% of the absorbed energy is dissipated as heat (according to the rule of energy conservation). Chemical composition of the coating matter that covers surfaces of metallic objects decides the attenuation of some wavelengths in the spectrum of illuminating light, whilst the mixture of light that is selectively reflected from a specific surface is decisive for the perception of colours (some metals may exhibit specific colours due to selective reflection of light, e.g. gold, copper) (Zhang et al., 2004; Tracton, 2006). The CCD matrix is a set of many light-sensitive sensors, where each sensor is capable to record and then reproduce an electric signal that is proportional to the amount of light that has illuminated the surface (the photoelectric effect – emission of electrons as a consequence of their absorption of energy from photons that reach the matter; the diagram of such energy conversion and the associated losses are shown in Fig. 1). The image-recording devices usually incorporate colour filters that are installed just upstream the light sensors and enable the intensity of a particular bandwidth within the light spectrum (a certain bandwidth of visible electromagnetic waves) to be recorded at a given location of the matrix. After processing by the central unit (CPU) the acquired information can be stored as digital images (graphic files) (Rafalowski, 2004). The analysis of histograms of digital images is very useful since it provides a great amount of information about the image that has been processed, including information about the range of brightness levels and the number of levels represented in the images. In the case of images acquired under suitable illumination conditions the histogram includes also quantitative information about the brightness of the image acquired for the photographed object. On the other hand, the 2-D co-occurrence matrices presented by Haralick in his studies (Haralick & Shanmugam, 1973; Haralick & Shapiro, 1992) are used for analyses of

Degradation of the gas turbine blade coating and its influence on the microstructure state of the superalloy

The technical condition of the blades has a critical influence on the reliability and life span of a gas turbine and an engine into which it is built in. The main causes of blade damage are overheating, creeping, thermal fatigue, high temperature corrosion, etc. It is often caused by adverse operational conditions or manufacturing defect, e.g. using insufficiently durable types of heat-resistant protective coatings or applied in an improper manner on the blade material. Reaction of coatings and blade material to mechanical and thermal loads depends mainly on the operating temperature of the turbine. Selection of a protective coating and material to manufacture a blade with an assumed strength must take into account its mechanical and thermal properties at maximum aerofoil temperature. The article presents characteristic forms of operational damages to the gas turbine blades of a turbojet aero engine. Distinguished were operational factors and their influence on the technical condition of coatings during the engine operation period. An influence of excess exhaust gas temperature on the condition of the heat-resistant blade layer was shown. Shown were also results of morphology tests of coating degradation types. Results of micro-structure tests of the blade superalloy after damage to the heat-resistant coating were also presented.

The New Approach to Identification of Parametric and Momentary Damages on the Basis of Lindeberg – Levy’s Model

Abstract The new approach for the assessment of reliability condition of the exploited system, based on the appropriate analysis of changes in the current parameters of technical condition aRb and the regulation condition aRc, determined from the compressed condition equation (1 and 2). While analyzing the course of momentary parameters for technical condition aRb and the regulation condition aRc, it was observed that the parametric and momentary damages can be identified on the basis of quantitative relations between momentary threshold value dpr and corresponding momentary permissible value dpr dop, which are calculated from equation (7, 8, 9) resulting from Lindeberg–Levy’s theorem. It is assumed that the damages are prevailing, when for the moment θi: >dpri> dpr dopi. With the number of damages (damage map), reliability parameters for each moment of exploitation of technical object (before the catastrophic damages will occur) can be determined. Parametric damages (expected lifetime E(T) and standard deviation of expected lifetime σE(T) provides the reasonable information for the appropriate planning of the servicing of exploitative objects.

Assessment of the technical condition of welds from Al alloy grade en an 5754 using the computed tomography method

Abstract The article presents selected results of tests conducted using the X-ray method with the application of a computed tomography device with a panel detector. The tests embraced samples of butt welds using aluminium alloy grade EN AN 5754, classified as an alloy for plastic processing with very good welding properties. The welds were executed using the TIG (Tungsten Inert Gas) method – arc welding using a non-consumable electrode in shielding gas. As a result of modernising the current welding process, it was possible to obtain better results of the welds’ technical condition assessed according to the number of welding defects.

Egzemplifikacja Tomograficznej Metody Do Oceny Jakości Połączeń Spawanych Ze Stopu EN 5754 H22

Streszczenie Jakość połączeń spawanych zależna jest od wielu czynników. Przedmiotowe normy określają warunki techniczne oceny jakościowej spawów, co stanowi podstawę do uznania połączenia za zgodne z wymaganiami lub wadliwe. W praktyce wykonanie połączenia spawanego całkowicie pozbawionego wad jest trudne. Do kontroli wewnętrznej struktury połączenia wykorzystać można nieniszczącą metodę z zastosowaniem przemysłowego tomografu komputerowego. Ta nowoczesna metoda diagnozowania łączy badanie rentgenowskie z zaawansowaną technologią komputerową. Podstawową zaletą tomografii komputerowej jest badanie obiektów w trzech wymiarach oraz możliwość wykonania rekonstrukcji przestrzennych. Celem artykułu jest omówienie wykorzystania tej metody do oceny jakości połączeń spawanych stopów aluminium. Możliwości tomografii komputerowej przedstawiono na przykładzie próbek spawalniczych wykonanych metodą TIG przy różnych parametrach procesu. Dokonano analizy jakości próbek wykazujących najmniejsze i największe zewnętrzne, jak również wewnętrzne wady spawalnicze.

Exemplification of Tomographic Method to Evaluate the Quality of Welded Joints Made from EN 5754-H22 Alloy

Abstract The quality of welded joints depends on many factors. The relevant standards stipulate technical conditions of welds quality assessment, which provides the basis for stating whether the given joint is compatible with the requirements or whether it is defective. In practice, making welded joints that are totally devoid of defects is extremely difficult. To conduct the control of inner structure of the given joint a non-destructive method with the application of industrial CT scanner might be applied. This modern diagnosing method combines the x-ray examination with advanced computer technology. The basic advantage of computer-assisted tomography consists in examining objects in three dimensions and the possibility to carry out three-dimensional reconstructions. The aim of this article is to discuss the use of this method to evaluate the quality of welded joints made of aluminium alloys. Capabilities of computer-assisted tomography were depicted by the case of weld probes constructed with TIG (ang. Tungsten Inert Gas) welding by different process variables. One has made the analysis of the quality of probes showing the smallest and the biggest internal and external welding defects.

The Active Thermography Method as Used to Assess the Bearing of Temperature on Thermophysical Properties of Superalloy of a Gas-Turbine Blade

The method of active thermography is an innovative NDT technology that was developed over the recent years to investigate microstructure condition of machinery components, including components of gas turbines. The essence of the method consists is examination of the thermal response of a material as a function of time to simulation by means of an external heat pulse. When the microstructure contains areas that differ in thermophysical properties, such differences entail alteration of the diffusion velocity. Therefore monitoring of the temperature field that spreads on the surface area of a workpiece that is being cooled down makes it possible to find locations of such different areas. The paper outlines initial results of investigations, carried out with use of the active thermography, how the temperature affects onto thermophysical properties demonstrated by superalloys used for construction of gas turbines. These investigations enabled to find out variations of thermophysical properties of these superalloys as a function of temperature. Eventually they laid down the fundamentals to undertake broader research studies in that domain. The core objective of the studies was to find out the relationships between variations of the thermal impact and corresponding amendments in the response signal received from the investigated material and to detect the correlations that have not yet been defined with sufficient accuracy. The described relationships and liaisons may contribute to development of fundamentals for the new NDT thermographic method suitable to evaluate the overheating status of gas turbine blades.

Assessment of Technical Condition Demonstrated by Gas Turbine Blades by Processing of Images for Their Surfaces / Oceny Stanu Łopatek Turbiny Gazowej Metodą Przetwarzania Obrazów Ich Powierzchni

Abstract The paper presents a non-destructive test method that makes it possible to assess condition of gas turbine blades based on the analysis of their images acquired in visible light. The results of high temperature’s influence on the condition of blades are revealed. The direct relationship between the temperatures of blades and discoloration of their surfaces is demonstrated. These relationships have been found out by the analysis of images in the form of first order statistical parameters derived wherefrom. The studies revealed alterations of the blade superalloy microstructures entailed by the effect of high temperature, hence the results in the form of first order statistical parameters could be correlated against alterations of the blade superalloy microstructures. Eventually, the variations of first order statistical parameters as well as variations of the blade superalloy microstructures could be determined as the functions of temperature. These relationships make it possible to assess how much the alloy microstructure is altered due to high temperature merely by discoloration of the blade surface. The innovative method can be used for in-flight evaluation of the superalloy overheating for gas turbine blades in operation. Streszczenie W artykule przedstawiono nieniszczącą metodę oceny stanu łopatek turbiny gazowej, opartej na przetwarzaniu obrazów ich powierzchni w świetle widzialnym. Zaprezentowano wyniki badań oddziaływania wysokiej temperatury na łopatki. Wykazano związki pomiędzy temperaturą wygrzewania łopatek, a zmianą barwy ich powierzchni. Związki te reprezentowano przez wyniki analizy obrazów w postaci parametrów statystyki pierwszego rzędu. Przedstawiono zmiany mikrostruktury nadstopu łopatek pod wpływem działania wysokiej temperatury. Wyniki w postaci statystyki pierwszego rzędu skorelowano z wynikami zmiany mikrostruktury nadstopu łopatek. W rezultacie otrzymano zależności parametrów statystyki pierwszego rzędu oraz zmiany mikrostruktury nadstopu łopatek w funkcji temperatury. Zależności te są przydatne do oceny zmian mikrostruktury w wyniku oddziaływania temperatury z wykorzystaniem zmian barwy powierzchni łopatek. Zaprezentowana metoda może służyć do oceny stanu przegrzania nadstopu podczas eksploatacji łopatek turbiny gazowej.

Analysis of feasibility to assess microstructure of gas turbine blades by means of the thermographic method

Analysis of Feasibility to Assess Microstructure of Gas Turbine Blades by Means of the Thermographic Method Operation of avionic turbine engines is always associated with possibility of various defects that may happen to turbine components, in particular to its blades. The most frequent reason for defects is overheating of the blade material but the thermal fatigue also occurs quite often. The most efficient examination method that provides plenty of information about structure of the investigated material of turbine blades is metallography but it is a destructive testing technology, so that the turbine no longer can be used after such investigation. This paper deals with methods of non-destructive tests that are currently in use and applicability of such methods to unbiased and trustworthy computer-aided diagnostics aimed to find out how the blade microstructure status varies in time. Results of initial examination of gas turbine blades are presented whereas the tests with use of the non-invasive thermographic method were carried out in order to assess condition of the blade material after the turbines had been subjected to the effect of high temperatures. Subsequently, the obtained results were successfully validated by means of the metallographic method. Eventually the conclusion could be made that the thermographic method makes it possible to achieve comprehensive and trustworthy information how microstructure of the blade materials is altered during the aircraft operation. Analiza możliwości oceny stanu mikrostruktury łopatek turbiny gazowej metodą termograficzną W procesie eksploatacji lotniczych silników turbinowych występują różnego rodzaju uszkodzenia elementów turbin, a zwłaszcza ich łopatek. Najczęstszą ich przyczyną jest przegrzanie materiału, a także zmęczenie cieplne łopatek. Mimo, iż badania metodą metalograficzną dostarczają informację o strukturze badanego materiału łopatek turbiny, to w rezultacie są to badania niszczące uniemożliwiające ich dalsze wykorzystanie. W artykule omówiono stosowane obecnie metody badań nieniszczących oraz możliwości ich wykorzystania do obiektywnego diagnozowania zmian stanu mikrostruktury łopatek turbin. Przedstawiono wyniki wstępnych badań łopatek turbiny gazowej poddanych wysokiej temperaturze z zastosowania nieinwazyjnej metody termograficznej do oceny stanu ich mikrostruktury. Wyniki te z powodzeniem zweryfikowano badaniami metodą metalograficzną. Stwierdzono, że metoda termograficzna umożliwia uzyskanie dobrej wiarygodności oceny stanu zmian mikrostruktury łopatek.