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1

Life and operational safety of power systems and chemical plants

Okrajni J.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 43, nr 1

38-63

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.

2

Low cycle fatigue of steels at high temperature under gradual loading

Okrajni J., Junak G.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 26, nr 2

147-150

EN

Purpose: The purpose of this paper is description of the creep resistant steels low cycle fatigue life under gradual loading. Design/methodology/approach: The low cycle test at high temperatures have been performed. This kind of fatigue is typical for materials worked at high temperature conditions. Findings: The model has been worked out in the work, which considers an influence of the loading sequence on the fatigue life of steels worked at a high temperature under mechanical loading. Research limitations/implications: The paper presents results of the part of research connected with methods of life prediction of materials worked under mechanical and thermal loading. From many aspects connected with the life criteria the work has been focused on the problem of the influence of the loading sequence on the fatigue life. This problem should be examined with many others when the durability of high temperature component is considered. Practical implications: The results of low-cycle fatigue could be useful in problems of quality assessment of the examined steels and in analysis of the influence of the character of loading on the material behaviour. Originality/value: The paper presents the own new description of the low cycle fatigue life of steels under gradual loading. The own new fatigue life criterion has been proposed.

3

Characterisation of properties and microstructural changes of 12% Cr-W steels after long-term service

Hernas A., Moskal G., Rodak K., Pasternak J.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 31, nr 2

312-319

EN

Purpose: Characterization of the influence of long-term exposition on microstructural stability and properties of new modified ferritic steels containing 12% Cr with W addition. Design/methodology/approach: The examinations were made on samples from superheater tubes (HCM12 and HCM12A type of steel) after long term exposition (20 and 30 thousand hours). The major technique used to investigations are: microstructural analysis with the use of LM, SEM and TEM and measurement of hardness and strength at an ambient temperature and at 600° C. Findings: Investigated power plant steels exhibit high stability of microstructeres and mechanical properties. The main effects of degradation are related to the decomposition of martensite areas, the precipitation of M23C6 carbides and Laves' phases, and the processes of recrystallization and recovery. Results of mechanical examinations showed that main mechanical parameters was still satisfactory after 30.000 hours of operation. Research limitations/implications: Presented examination showed that new type of power plant steels are characterized by high stability of the microstructure and properties, however it necessary to identify the mechanisms of structure degradation and, in consequence, of adjusting the mechanical properties below the values required. It is therefore necessary to continue the investigations after successive periods of operation. Practical implications: Presented conclusion give the possibility to the determination of the degree of life-time lost of the investigated high-chromium steels and specification of the time of safety operation. Originality/value: This investigations are valuable contribution to the development of new steels for the power industry. They enable the identification of the degradation mechanisms in steels of new types, which enhances the durability and safety of boilers' operation.

4

Steam pipelines' effort and durability

Okrajni J., Mutwil K., Cieśla M.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 22, nr 2

63-66

EN

Purpose: The main problem addressed in the paper is the description of an effort and durability of steam pipelines under the conditions of mechanical and thermal interactions. Design/methodology/approach: The FEM modelling has been used to determine the stress and strain fields in the pipelines and to describe their behaviour under mechanical and thermal loading. Findings: An appropriate model 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. The analysis made has shown that the most probable cause of cracks occurence on the analyzed chosen pipeline' inner surfaces are thermal deformations and constraints of their dislocations. 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.

5

Crack initiation in steel parts working in boilers and steam pipelines

Renowicz D., Cieśla M.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 21, nr 2

49-52

EN

Purpose: The purpose of this paper is to identify the influence of loading history and the processes of material degradation on the crack initiation and on durability under thermo-mechanical fatigue conditions. Design/methodology/approach: Based on the operation data, the conditions of laboratory examinations of specimens were determined. A specialist apparatus unit was used for the examination, enabling the simulation of any spectrum of mechanical load and temperature changes. Findings: The material durability criterion has been defined based on an energy related approach to the problem of crack initiation in steels which work under thermal fatigue conditions. Research limitations/implications: In the case discussed, i.e. a pipeline part, the present criteria should be expanded with critical values describing the total length of cracks initiated on the internal surface of a specimen. Practical implications: The paper refers to the research on steel 10H2M (10CrMo.910) used in the conventional boilers, superheaters and pipelines in power plants. Originality/value: Originality of the paper is the methodology of the lifetime prediction of steam pipeline parts working in thermo-mechanical fatigue conditions.

6

Properties and microstructure of 12% Cr-W steels after long-term service

Hernas A., Moskal G., Rodak K., Pasternak J.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 17, nr 1-2

69--72

EN

Purpose: The purpose of the research was to identify the influence of long-term exposition on stability of the microstructure and properties of new ferritic steels containing 12% Cr with W addition. Design/methodology/approach: The research allowed the identification of microstructural changes that takeplace during long-term operation and their influence on the mechanical properties. The examinations wereconducted on superheater tubes (HCM12 and HCM12A steel) after 20 and 30 thousand hours of exposition. The scope of the research encompassed a microstructural analysis with the use of LM, SEM and TEM andmeasurement of hardness and strength at an ambient temperature and at 600oC. Findings: It was found that the steels showed high stability of structures and mechanical properties. The mainsymptoms of degradation are connected with the decomposition of martensite areas, the precipitation of M23C6 carbides and Laves’ phases, and the processes of recrystallization and recovery. The level of all mechanical parameters was still satisfactory after 30,000 hours of operation. Research limitations/implications: The discussed research proves high stability of the microstructure and properties of the investigated steels, however it necessary to identify the mechanisms of structure degradation and, in consequence, of adjusting the mechanical properties below the values required. It is therefore necessary to continue the investigations after successive periods of operation. Practical implications: The results obtained allow the determination of the degree of life-time lost of the investigated high-chromium steels and specification of the time of safety operation. Originality/value: The results obtained are valuable contribution to the development of new steels for the power industry. They enable the identification of the degradation mechanisms in steels of new types, which enhances the durability and safety of boilers’ operation.