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PL
W pracy przedstawiono przykłady modelowania procesów cieplno-mechanicznych zachodzących w rurach grubościennych podczas uruchamiania bloków energetycznych. Rozpatrzono przykłady elementów wykonanych ze stopu HR6W przeznaczonego na elementy urządzeń energetycznych o podwyższonych parametrach pracy. Omówiono zagadnienie wyznaczania pól temperatury i składowych stanu naprężenia na przykładzie rury grubościennej o średnicy zewnętrznej wynoszącej 540 mm i grubości ściany równej 127 mm, która reprezentuje elementy bloków o nadkrytycznych parametrach pracy, projektowane z uwagi na kryterium wytrzymałości na pełzanie. Ciśnienie wewnątrz rury w warunkach pracy ustalonej wynosiło 31,4 MPa, a temperatura 610°C. Skoncentrowano się na zagadnieniu oceny wpływu krótkotrwałych zmian temperatury podczas cykli uruchamiania bloku energetycznego na rozkłady zmiennej w czasie temperatury i związane z nimi naprężenia cieplne. Przedstawiono sposób modelowania uwzględniający możliwość oceny wpływu czasu rozruchu i niestabilności parametrów pary w tym okresie na przebieg lokalnych charakterystyk procesu odkształcania materiału. Ważne dla symulacji numerycznej właściwości materiałowe przyjmowano jako zależne od temperatury. Wyznaczono lokalne charakterystyki odkształcania wybranych punktów na powierzchni rury w postaci zależności pomiędzy odkształceniem i naprężeniem obwodowym. Wykazano istotny wpływ oscylacji temperatury występujących w warunkach rozruchu na zmienne w czasie pola naprężeń i odkształceń, sprzyjające powstawaniu zjawisk o zmęczeniowym charakterze.
EN
The examples of simulation of thermo-mechanical processes which undergo during start-up of commercial power boilers in thick-walled tubes have been presented. The tubes were made of nickel alloy HR6W. This material will be used for thick-walled elements of future boilers with raised operation parameters. The determination of temperature distribution and components of stress state was carried out for the tube with an outer diameter of 540 mm and wall thickness of 127 mm. The analysed heavy wall tube represents the elements of super-critical unit designed due to creep strength. The pressure inside the tube, under steady-state conditions, was 31.4 MPa and temperature was equal to 610°C. The investigations were focused on assessment of the effect of transient changes in temperature during start-up cycles of power unit on distributions of time-dependent temperature and thermal stresses. The method of modeling that allows to assess the effect of start-up time and instability of steam parameters on the local characteristics of the material deformation. The important material properties for the numerical simulation were assumed in relation to the temperature. The local characteristics of deformation of selected points lying on tube surface in a form of relations between strain and circumferential stress were determined. It has been shown that temperature change oscillations under start-up of boiler has an important effect on the time-dependent stress and strain distributions, intensifies the fatigue phenomena.
EN
This paper presents an attempt at the numerical modelling of a model that has been developed for a glass-fiber reinforced epoxy laminate (10-layer) square plate, supported on a circular support and loaded centrally with a spherical indenter. The determination of the stress corresponding to the initiation of the material failure process under such loading conditions has also been presented. ALGOR software was used for the numerical modelling. It was found that the performed analysis can be efficiently used to evaluate the properties of a material subjected to a compound stress state. This has been proven effective to determine the stress level in the material. The analysis of the determined characteristics based on the evaluation of the load value oscillation amplitude in the final portion of the curve may be proposed for detecting the moment of failure initiation in materials during mechanical tests.
PL
Artykuł jest kontynuacją pracy pt. Behaviour of plain-woven glass-fiber reinforced polymer laminate plates during symmetrical bending on a circular support – Part I: Experimental evaluation [14]. Jego celem jest wyznaczenie naprężenia w próbce laminatu podpartej na podporze kołowej i obciążanej centralnie za pomocą modelowania numerycznego i z wykorzystaniem danych eksperymentalnych uzyskanych we wspomnianej pierwszej części pracy. Po ustaleniu skutecznej procedury obliczania naprężenia będzie możliwe wyznaczenie naprężenia odpowiadającego początkowi procesu zniszczenia w materiale oraz ocena zachowania się laminatu w założonych, bardzo skomplikowanych, warunkach obciążania.
EN
This paper presents an attempt at the experimental evaluation of the behaviour of a glass-fiber reinforced epoxy laminate (10-layer) square plate, supported on a circular support and loaded centrally with a spherical indenter. The determination of the moment of the initiation of the material failure process under such loading conditions has been performed with use of photographic method. It was found that the performed test can be efficiently used to evaluate the properties of a material subjected to a compound stress state. However, due to high complexity of the issue mathematical calculation of stress is practically impossible. In order to determine the stress in the loaded laminate a numerical modelling should be applied. It is planned to be performed in separate study.
PL
Eksperymentalna analiza zachowania laminatu w warunkach dwuosiowego obciążenia ma bardzo duże znaczenie poznawcze. Jest to sposób obciążania, który często pojawia się w rzeczywistych warunkach, w których laminaty są stosowane — dotyczy to m.in. wszelkiego rodzaju płyt. Przykładem takiego zastosowania może być poszycie samolotu lub statku wodnego. Poznanie zachowania laminatu cechującego się ortotropią właściwości sprężystych, podczas dwuosiowego obciążania, umożliwia odniesienie uzyskanych wyników do wyników badań w warunkach jednoosiowych (zginanie, rozciąganie) i wyciągnięcie wniosków na temat skuteczności badań w warunkach jednoosiowych w zakresie oceny laminatu jako bezpiecznego materiału konstrukcyjnego. W pracy przedstawiono próbę eksperymentalnej oceny właściwości płyty z 10-warstwowego laminatu epoksydowego wzmacnianego włóknem szklanym, wspartej na kołowej podporze i symetrycznie obciążanej za pomocą sferycznego wgłębnika. Celem pracy jest określenie zachowania laminatu przy obciążaniu powierzchniowym ze szczególnym uwzględnieniem wyznaczenia charakterystyki siłowo-przemieszczeniowej oraz określenia momentu inicjacji procesu jego zniszczenia w zadanych warunkach obciążeniowych. Uzyskane wyniki będą stanowić podstawę do walidacji modelu numerycznego przeznaczonego do wyznaczania naprężeń w próbach symetrycznego obciążania płyt. Model numeryczny będzie przedmiotem odrębnego studium, będącego kontynuacją tej pracy.
PL
Przedstawiono konsekwencje powstawania pęknięć spowodowanych zmęczeniem i korozją na przykładzie rurociągu wody zasilającej bloku 120 MW. Poddano analizie wpływ owalizacji na wartości naprężeń w kolanach rurociągu. Obliczenia wykonano dla danych uzyskanych na podstawie badań diagnostycznych dwóch rurociągów wody zasilającej bloku 120 MW. Na podstawie przeprowadzonych rozważań określono przyczynę powstania uszkodzenia oraz zaproponowano metody zapobiegania podobnym uszkodzeniom w rurociągach wody zasilającej.
EN
Consequences of the cracks formation caused with the fatigue and the corrosion of the feed water pipeline in the block 120MW, which was taken as an example, have been presented in the paper. The analysis the influence of an oval on values of stresses in elbows of the pipelines has been shown. Calculations were executed for data obtained from diagnostic research of two feed water pipelines of the block 120 MW. On the base of carried out considerations the reason of the damage has been assessed and methods of the prevention of similar damage in pipelines of the feed water have been proposed.
EN
The study focuses on the problem of determination of low-cycle fatigue properties for the chosen group of creep-resistant steels used in the power and chemical industries. It tries to find the parameter which would describe well the fatigue life and take into account mechanical loads and temperature. The results of LCF tests have been presented in the paper. New parameter P has been introduced. This parameter joins a plastic strain range, a stress range and temperature. The fatigue life has been predicted versus parameter P. The comparison of the predicted and observed values of fatigue life shows the agreement between these values. The method of fatigue life prediction formulated in this way is expected to describe the behavior of materials under thermo-mechanical fatigue.
PL
W artykule przedstawione zostały podstawowe oddziaływania występujące w elementach urządzeń energetycznych. Rozpatrzono procesy pełzania, relaksacji naprężeń i zmęczenia. W celu wyznaczenia charakterystyk tych procesów zastosowano metody komputerowego modelowania. Opisano sposób wyznaczania charakterystyk odkształcania oraz wykazano, że skutkiem każdego z rozpatrywanych rodzajów obciążeń jest odmienne zachowanie się elementów instalacji i odmienne charakterystyki powinny być stosowane do opisu zjawisk powstawania uszkodzeń w poddanych analizie elementach. Podkreślono istotną rolę zmęczenia cieplno-mechanicznego w grubościennych elementach bloków energetycznych o podwyższonych parametrach pracy.
EN
Basic loads in power plants components have been presented in the paper. The creep, the stress relaxation and fatigue processes have been discussed. Methods of the computer modelling have been used to describe the characteristics of these processes. The method of the evaluation of the stress-strain characteristics has been presented. It has been justified that each of considered loads leads to the different behaviour of the components and different characteristics should be applied to the description of phenomena of the formation of damage in components under consideration. The crucial role of the thermo-mechanical fatigue of thick-walled components of boilers which operate under increased temperature and pressure has been underlined.
PL
W pracy przedstawiono sposób rozwiązania zagadnienia ograniczenia amplitudy przemieszczeń układu mocującego separatora, w którego zawieszeniach stwierdzono obecność pęknięć spowodowanych procesem zmęczenia materiału w warunkach pracy. Przedstawiono wyniki analizy modalnej oraz charakterystyki zmiennych w czasie przemieszczeń wybranych punktów układu wyznaczonych przy zadanych wymuszeniach na podstawie analizy dynamicznej. Porównano ze sobą rozwiązanie istniejące oraz nowe rozwiązanie konstrukcyjne, które zapewnia zmniejszenie amplitudy drgań mechanicznych występujących w warunkach eksploatacji.
EN
The study presents a way of solving a limit of amplitude problems of displacement the fastening system of the water separator, in suspensions which found the presence of cracks, caused by fatigue in the working conditions. The results of modal analysis and time-varying characteristics of displacements the selected points of the system, designated by selected extortion based on dynamic analysis were shown. Existing system and new design solution, which ensures reduction of mechanical vibrations amplitude occurring in operating conditions were compared.
PL
Głównym celem badań przedstawionych w pracy jest opis zachowania się elementów urządzeń energetycznych poddanych oddziaływaniu obciążeń mechanicznych i cieplnych. Jako metodę badań zastosowano komputerowe modelowanie przy użyciu metody elementów skończonych w połączeniu z pomiarami temperatury w warunkach przemysłowych. Porównano wyniki pomiarów z rezultatami ujęcia modelowego i wykazano, że ujęcie modelowe stosujące metodę elementów skończonych umożliwia uzyskanie zadowalającego opisu zmiennego w czasie pola temperatury.
EN
The main purpose of this work is to determine the behaviour of power plant components operating under mechanical and thermal loading. Computer FEM modelling of temperature fields along with temperature measurements in the industry conditions have been applied as the methods of research. The results of modelling and measurements have been compared and possibility of using the FEM modelling for the proper description of the changeable with time temperature fields has been shown.
9
Content available remote Boundary conditions in models of power plant components under thermal loading
EN
Purpose: The main purpose of the work is the description of conditions of fatigue process of power plant components working under mechanical and thermal loading. The work focuses on the chosen component characteristics. The issue of influence of the heat transfer conditions on the component surface on stresses changes in time has been discussed. Design/methodology/approach: The FEM modelling method has been used to describe the behaviour of the chosen component. The models have been validated on the basis of temperature measurements during operation period. Findings: It has been shown that the determination of the effects induced by unsteady conditions of start-up and shut-down of installations requires application of unconventional methods of research and analysis of their results. In such a case, a methodology can be applied consisting in combining the methods of computer modelling of temperature fields with temperature measurements in selected points of the component. Research limitations/implications: The presented analysis is the part of the complex investigation method which main purpose is increasing the accuracy of the thermo-mechanical fatigue process description. In such situation the investigations curried out in the work give the model approach and data for the comparison the real behaviour with the predictions. However the work is focused only on the chosen component and chosen characteristics of loading. Practical implications: The method of the chosen component behaviour analysis used in the paper could be useful in the practical cases when the real components mechanical behaviour would be analysed and their fatigue life would be assessed. Originality/value: The main value of this paper is the own method of the mechanical behaviour analysis of the power plant components. This method includes FEM modelling and assumption that the heat transfer coefficient should be treated as dependent on time. The material stress-strain behaviour has been treated as the local phenomenon that could be modelled.
EN
Purpose The main purpose of the work is the description of the low-cycle fatigue process of mine powered roof supports working under mechanical high loading. The work focuses on the chosen component strain-stress characteristics. The issue of modelling the stress-strain behaviour of powered roof supports components during low-cycle fatigue has been discussed. Design/methodology/approach: The FEM modelling and Neuber’s method have been used to describe the local stress-strain behaviour of the chosen component. Findings: In the examined devices, variable stress and strain values were calculated for a chosen characteristic load cycle. Diagrams in the form of a hysteresis loop determined using Neuber’s hypothesis and FEM were compared. The values of the range of equivalent strain determined for multiaxial stress states using the finite element method proved to be close to those estimated via Neuber’s method. Research limitations/implications: The presented analysis is the part of the complex investigation method which main purpose is increasing the accuracy of the low-cycle fatigue process description. In such situation the investigations curried out in the work give the model approach and data for the comparison the real behaviour with the predictions. However the work is focused only on the chosen component and chosen characteristics of loading. Practical implications: The method of stress-strain behaviour analysis used in the paper could be useful in the practical cases when the real components mechanical behaviour would be analysed and their fatigue life would be assessed. Originality/value: The main value of this paper is the own method of the mechanical behaviour analysis of the powered roof support component. This method includes FEM modelling and Neuber’s method of the stress-strain characteristics assessment. The material stress-strain behaviour has been treated as the local phenomenon that could be modelled.
PL
Przedstawiono analizę zachowania się wodooddzielacza bloku energetycznego wraz z układem zawieszeń. Pęknięcia cięgien tych zawieszeń powstawały w wyniku drgań wywołanych turbulentnym przepływem mieszanki wodno-parowej kotła. Analiza modalna i numeryczna symulacja drgań modelu układu pozwoliła na opracowanie dodatkowego układu tłumiącego, zabezpieczającego elementy zawieszeń wodooddzielacza przed zmęczeniowym pękaniem.
EN
Presented is the analysis of behaviour of a power unit water separator with is suspension system. Cracks in the suspension tension members occurred as a result of vibrations caused by the boiler water-steam mixture turbulent flow. Modal analysis and numerical simulation of the circuit model vibrations enabled elaboration of an additional vibration damping system protecting the water separator suspension elements against fatigue cracking.
12
Content available remote Modelowanie procesu zmęczenia cieplno-mechanicznego
EN
The main purpose of the work is the method of the description of the thermo-mechanical fatigue process of power plant components working under mechanical and thermal loading. The work focuses on the chosen component strain- stress characteristics. The FEM modelling has been used to describe the local stress- strain behaviour of the chosen power plant element. The calculations of stress distribution on the component surface show that the internal pressure induces considerably smaller values of stresses and strains in comparison with the same stresses specified for thermal loads. Thus, thermal impacts are responsible for cracks initiation and growth in areas of the greatest intensity of damage accumulation. The presented analysis is the part of the complex investigation method which main purpose is increasing the accuracy of the TMF process description and thermo-mechanical life assessment. In such situation the industrial investigations curried out in the work give the model approach and data for the comparison the real behaviour with the predictions.
EN
Purpose: The main purpose is the method of the description of the thermo-mechanical fatigue process of power plant components working under mechanical and thermal loading. The work focuses on the chosen component strain-stress characteristics and their strength. The paper discusses the issue of modelling the heating and cooling processes of components in a power plants in the start-up and shut-down conditions of a boiler. Design/methodology/approach: The FEM modelling has been used to describe the local stress-strain behaviour of the chosen component. Findings: The calculations of stress distribution on the chosen component surface show that the internal pressure induces considerably smaller values of stresses and strains in comparison with the same stresses specified for thermal loads. However, it should be noted that the impact of temperature gradients and thermal stresses is usually short-lived, therefore, its influence on creep processes is less significant in comparison to pressure load. Material fatigue is mainly the effect of thermal stresses. Thus, thermal impacts are responsible for cracks initiation and growth in areas of the greatest intensity of damage accumulation. Research limitations/implications: The presented analysis is the part of the complex investigation method which main purpose is increasing the accuracy of the TMF process description and thermo-mechanical life assessment. The possibility of applying the fatigue durability criteria currently assumed in standards still requires justification and confirmation in laboratory and industrial conditions to be closer to the real components behaviour. In such situation the industrial investigations curried out in the work give the model approach and data for the comparison the real behaviour with the predictions. Practical implications: The method of stress-strain behaviour analysis used in the paper could be useful in the practical cases when the real components mechanical behaviour would be analysed. Originality/value: The main value of this paper is the own method of the mechanical behaviour analysis of the power plant component. This method includes the temperature fields analysis taking into account the boundary conditions based on the operation parameter data and the thermoplastic material model. The material stress-strain behaviour has been treated as the local phenomenon, that could be modelled by FEM.
PL
W pracy analizowano mechaniczne uwarunkowania procesu pękania warstwy aluminidkowej na stopie ŻS6U w warunkach zmęczenia cieplno-mechanicznego. W analizach wykorzystano wyniki obliczonych numerycznie rozkładów naprężeń. Otrzymane rozkłady naprężeń umożliwiły opracowanie modeli mechanicznego zachowania warstwy by(T). Dokonano również oceny wytrzymałości elementów z aluminidkową warstwą ochronną, poddanych oddziaływaniu zmiennej w czasie temperatury i stałego obciążenia mechanicznego. Charakterystyki procesu zmęczenia warstwy mogą stanowić jeden z elementów metody oceny wpływu podstawowych własności fizycznych oraz cech geometrycznych warstw aluminidkowych, wytworzonych na elementach stosowanych w silnikach lotniczych na procesy powstawania i rozwoju pęknięć.
EN
The determinants of the cracking process of an aluminide coating on alloy ŻS6U which occurs under thermomechanical fatigue conditions have been analyzed in the study. The results of numerically calculated stress distributions were used in the analyses. The resultant stress distributions enabled the development of mechanical behaviour models of the by(T) coating. An evaluation was also made of the strength of elements with an aluminide protective layer, subjected to a variable in time temperature and to constant mechanical loading. The characteristics of the coating fatigue process may constitute one of the elements of the method to evaluate the effect of the basic physical properties and geometric features of aluminide coatings, fabricated on elements used in aircraft engines, on the processes of crack formation and growth.
PL
Przedstawiono zagadnienie badania zachowania się elementów poddanych zmęczeniu cieplno-mechanicznemu. Skoncentrowano się na opisie przebiegu procesu odkształcania na przykładzie wybranego obiektu pracującego w przemyśle energetycznym. Przedstawiono metodykę wyznaczania charakterystyk procesu zmęczeniowego w postaci pętli histerezy w układzie odkształcenie mechaniczne - naprężenie. Modelując zachowanie się rozpatrywanego elementu zastosowano metodę elementów skończonych. Wyniki obliczeń naprężeń i odkształceń na powierzchni rozpatrywanego elementu wykazały, że naprężenia i odkształcenia spowodowane ciśnieniem wewnętrznym są znacznie mniejsze od naprężeń i odkształceń spowodowanych obciążeniami mechanicznymi. Można na tej podstawie wyciągnąć wniosek, że za powstawanie i rozwój pęknięć w obszarach o największym wytężeniu odpowiedzialne będą w głównej mierze obciążenia cieplne. Przedstawione w pracy rozważania reprezentują fragment metodyki badań złożonych procesów zmęczenia cieplno-mechanicznego koncentrując się na modelowaniu zjawisk zachodzących w warunkach tego procesu i porównaniu wyników analizy teoretycznej z badaniami eksperymentalnymi.
EN
The main purpose of the work is the method of the description of the thermo-mechanical fatigue process of power plant components working under mechanical and thermal loading. The work focuses on the chosen component strain-stress characteristics. The FEM modelling has been used to describe the local stress-strain behaviour of the chosen power plant element. The calculations of stress and strain distribution on the component surface show that the internal pressure induces considerably smaller values of stresses and strains in comparison with the same stresses and strains specified for thermal loads. Thus, thermal impacts are responsible for cracks initiation and growth in areas of the greatest intensity of damage accumulation. The presented analysis is the part of the complex investigation method which main purpose is increasing the accuracy of the TMF process description and thermo-mechanical life assessment. In such situation investigations curried out in the work give the model approach and data for the comparison the real behaviour with the predictions.
PL
Przedstawiono jeden z wielu przykładów zastosowania metod modelowania komputerowego do oceny zmiennych w czasie pól temperatury i naprężeń w urządzeniach energetycznych. Omówiono zagadnienie wyznaczania rozkładów naprężeń w elementach grubościennych rurociągów energetycznych w nieustalonych warunkach pracy podczas uruchamiania bloku energetycznego. Wykazano możliwość wykorzystania pomiarów temperatury pary oraz temperatury wybranych punktów rozpatrywanych elementów do zdefiniowania warunków brzegowych zagadnienia modelowania przepływu ciepła oraz do sprawdzenia poprawności działania opracowanych modeli komputerowych. Wykazano istotne znaczenie zmiennego w czasie i nierównomiernego pola temperatury na przebieg lokalnych zmian naprężeń, których skutkiem są procesy zmęczenia materiału.
EN
Presented is one of the many examples of computer modelling methods application for evaluation of the variable in time temperature and stress fields in power installations. Discussed is the problem of determining stress patterns in elements of thick-walled power pipelines in transient working conditions during a power unit start-up. There is proved a possibility to use measurements of steam temperature and the temperature of selected points of the investigated elements for defining boundary conditions of the heat transfer modelling problem as well as to verify operative correctness of the elaborated computer models. Shown is essential importance of time-variable and non-uniform temperature field for the course of local stress changes that results in metal fatigue processes.
17
Content available remote Life and operational safety of power systems and chemical plants
EN
Purpose: The problem addressed in the paper is the description of an effort and durability of components under the conditions of mechanical and thermal interactions. The problems of proper material testing methods have been shown as the important part of the components life assessment methodology. Design/methodology/approach: The FEM modelling has been used to determine the stress and strain fields in the components and to describe their behaviour under mechanical and thermal loading. Findings: An appropriate models description has been developed. So far, experimental verification of the usefulness of the model description to determine the stress and strain patterns in particular object and for chosen operation conditions has been made. Research limitations/implications: The developed description should be useful in problems of behaviour predictions of high temperature components and their durability assessment under different mechanical and thermal loadings in industry practical applications. Originality/value: The method, which more precise description of power industry components behaviour makes possible have been shown in the work. The work is addressed to researchers interested in problems of component behaviour prediction under different loadings that we can meet in the operation practice and to power industry engineering maintenance staff.
18
EN
Purpose: The paper discusses the issue of modelling the heating and cooling processes of T-pipes in a power plant pipeline in the start-up conditions of a boiler. The main purpose of this work is the description of the mechanical behaviour of power plant components working under mechanical and thermal loading and validation of the computer modelling methods. Design/methodology/approach: The FEM modelling has been used to describe the local stress-strain behaviour of the chosen component. Findings: The reasons for the presence of high and variable in time temperature gradients in the components of the main steam pipeline include, among other things, variable values of the coefficient of heat transfer between the pipeline material and the medium flowing inside it, which, at this stage of boiler operation, may change its state. Unsteady operation of a pipeline, especially in case of subsequent boiler start-ups, may induce thermal stresses which exceed the values of allowable stress in components of complex shapes. Research limitations/implications: The possibility of applying the durability criteria currently assumed in standards still requires justification and confirmation in laboratory and industrial conditions to be closer to the real components behaviour. In such situation the presented analysis is the part of the complex investigation method which main purpose is increasing accuracy of the TMF process description and thermo-mechanical life assessment. Practical implications: The calculations carried out may constitute a basis for developing a material test parameters which would bring closer the fatigue conditions appearing locally in the analysed components. The method of stress-strain behaviour analysis used in the paper could be useful in the practical cases when the real components mechanical behaviour would be analysed. Originality/value: The main value of this paper is the own method of the mechanical behaviour analysis of the power plant component. This method includes the temperature fields analysis taking into account the boundary conditions based on the operation parameter data and the thermoplastic material model. The material stress-strain behaviour has been treated as the local phenomenon, that could be modelled by FEM.
19
Content available remote Thermo-mechanical fatigue conditions of power plant components
EN
Purpose: The main purpose of this work is the description of the mechanical behaviour of power plant components working under mechanical and thermal loading that cause the thermo-mechanical fatigue fracture in selected areas of the component surfaces. Design/methodology/approach: The computer modelling has been used to describe the local stress-strain behaviour of the chosen component. Findings: The values of variable in time temperature strains and stresses in selected points of the power plant header were determined. The points were located at the edges of holes through which water steam is supplied and carried away, where under use conditions the presence of cracks can be observed. That stresses and mechanical strains caused by the influence of a non-uniform temperature field may be significantly higher in comparison with the stresses and strains caused by the pressure inside the analysed component. Tensile thermal stresses of high values are created especially under conditions of sudden cooling during unsteady work of a power unit. Research limitations/implications: The possibility of applying the durability criteria currently assumed in standards still requires justification and confirmation in laboratory and industrial conditions to be closer to the real components behaviour. In such situation the presented analysis is the part of the complex investigation method which main purpose is increasing accuracy of the TMF process description and thermo-mechanical life assessment. Practical implications: The calculations carried out may constitute a basis for developing a material test parameters which would bring closer the fatigue conditions appearing locally in the analysed components. The method of stress-strain behaviour analysis used in the paper could be useful in the practical cases when the real components mechanical behaviour would be analysed. Originality/value: The main value of this paper is the own method of the mechanical behaviour analysis of the power plant component. This method includes the temperature fields analysis taking into account the boundary conditions based on the operation parameter data and the thermoplastic material model. The material stress-strain behaviour has been treated as the local phenomenon, that could be modelled by FEM.
EN
Purpose: This study sets out to determine the characteristics of high-temperature creep resisting steels under conditions of thermo-mechanical fatigue with the use of a method proposed in the Code-of-Practice under the EU TMF-Standard project. Design/methodology/approach: The thermo-mechanical fatigue (TMF) tests were carried out in the conditions where the value of complete strain and the temperature were under control. Two methods of investigating samples in TMF tests were applied: OP (out-of-phase) and IP (in-phase). Findings: Based on the tests, the characteristics of TMF life was determined and it was found that X20CrMoV12.1 steel shows lower life in comparison with new steels: X10CrMoVNb9-1 (T/P91) and X10CrWMoVNb9-2 (T/P92). The results of the OP tests made for X10CrMoVNb9-1 (T/P91) steel are an exception here. Tests of thermo-mechanical fatigue have shown that in a majority of cases in fatigue tests, the X20CrM0V12.1 steel has lower TMF life when compared to X10CrMoVNb9-1 (T/P91) and X10CrWMoVNb9-2 (T/P92) steels, despite its better strength properties, as a measure of which, the range of stress was adopted. Research limitations/implications: At the present stage of the research, two types of tests (IP and PO) were performed. Due to a limited number of experiments connected with the application of selected types of tests and their number, the conclusions resulting from the research may, at the present stage, serve as guidelines for its continuation only. Practical implications: The test results may also be used to compare the properties of creep resisting steels used in the power engineering industry and represent a contribution to widening the knowledge of the behaviour of materials under thermo-mechanical fatigue conditions. Originality/value: This study is one of the first attempts to determine the TMF life characteristics of the steels used in the Polish power engineering industry.
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