The Experts below are selected from a list of 138 Experts worldwide ranked by ideXlab platform
Bratislav Rajicic - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen damage of steels: A case study and Hydrogen embrittlement model
Engineering Failure Analysis, 2015Co-Authors: Milos B. Djukic, Gordana M. Bakic, Vera Šijački-žeravčiĆ, Aleksandar Sedmak, Bratislav RajicicAbstract:Many efforts have been made to understand the effects of Hydrogen on steels, resulting in an abundance of theoretical models and papers. However, a fully developed and practically applicable predictive physical model still does not exist industrially for predicting and preventing Hydrogen damage. In practice, it is observed that different types of damages to industrial boiler components have been associated with the presence and localization of Hydrogen in metals. In this paper, a damaged boiler tube made of grade 20 - St.20 (or 20G, equivalent to AISI 1020) was investigated. The experimental research was conducted in two distinctive phases: failure analysis of the boiler evaporator tube sample and subsequent postmortem analysis of the viable Hydrogen embrittlement mechanisms (HE) in St.20 steel. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature Hydrogen Attack (HTHA) during service, as a result of the development of Hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, tube wall thickness measurement, tensile testing, hardness measurement, impact strength testing (on instrumented Charpy machine), analysis of the chemical composition of corrosion products - deposit and the microstructural characterization by optical and scanning electron microscopy - SEM/EDX. The HTHA damage mechanism is a primary cause of boiler tube fracture. Based on the multi-scale special model, applied in subsequent postmortem investigations, the results indicate a simultaneous action of the Hydrogen-enhanced decohesion (HEDE) and Hydrogen-enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of Hydrogen in investigated steel. The model is based on the correlation of mechanical properties to the SEM fractography analysis of fracture surfaces.
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Hydrogen Embrittlement of Low Carbon Structural Steel
Procedia Materials Science, 2014Co-Authors: Milos B. Djukic, Gordana M. Bakic, Vera Sijacki Zeravcic, Aleksandar Sedmak, Bratislav RajicicAbstract:Hydrogen embrittlement (HE) of steels is extremely interesting topic in many industrial applications, while a predictive physical model still does not exist. A number of studies carried out in the world are unambiguous confirmation of that statement. Bearing in mind multiple effects of Hydrogen in certain metals, the specific mechanism of Hydrogen embrittlement is manifested, depending on the experimental conditions. In this paper structural, low carbon steel, for pressure purposes, grade 20 -St.20 (GOST 1050-88) was investigated. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature Hydrogen Attack and HE during service, as a result of the development of Hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, hardness measurement, impact strength testing (on instrumented Charpy machine) and microstructural characterization by optical and scanning electron microscopy -SEM/EDX. Based on multi-scale special approach, applied in experimental investigations, the results, presented in this paper, indicate the simultaneous action of the Hydrogen-enhanced decohesion (HEDE) and Hydrogen enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of Hydrogen in investigated steel. These results are consistent with some models proposed in literature, about a possible simultaneous action of the HELP and HEDE mechanisms in metallic materials.
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20th European Conference on Fracture (ECF20) Hydrogen embrittlement of low carbon structural steel
2014Co-Authors: Milos B. Djukic, Vera Sijacki Zeravcic, Aleksandar Sedmak, Gordana Bakić, Bratislav RajicicAbstract:Abstract Hydrogen embrittlement (HE) of steels is extremely interesting topic in many industrial applications, while a predictive physical model still does not exist. A number of studies carried out in the world are unambiguous confirmation of that statement. Bearing in mind multiple effects of Hydrogen in certain metals, the specific mechanism of Hydrogen embrittlement is manifested, depending on the experimental conditions. In this paper structural, low carbon steel, for pressure purposes, grade 20 - St.20 (GOST 1050-88) was investigated. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature Hydrogen Attack and HE during service, as a result of the development of Hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, hardness measurement, impact strength testing (on instrumented Charpy machine) and microstructural characterization by optical and scanning electron microscopy - SEM/EDX. Based on multi-scale special approach, applied in experimental investigations, the results, presented in this paper, indicate the simultaneous action of the Hydrogen-enhanced decohesion (HEDE) and Hydrogen enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of Hydrogen in investigated steel. These results are consistent with some models proposed in literature, about a possible simultaneous action of the HELP and HEDE mechanisms in metallic materials. © 2014 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of the Norwegian University of Science and Technology (NTNU), Department of Structural Engineering .
Milos B. Djukic - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen damage of steels: A case study and Hydrogen embrittlement model
Engineering Failure Analysis, 2015Co-Authors: Milos B. Djukic, Gordana M. Bakic, Vera Šijački-žeravčiĆ, Aleksandar Sedmak, Bratislav RajicicAbstract:Many efforts have been made to understand the effects of Hydrogen on steels, resulting in an abundance of theoretical models and papers. However, a fully developed and practically applicable predictive physical model still does not exist industrially for predicting and preventing Hydrogen damage. In practice, it is observed that different types of damages to industrial boiler components have been associated with the presence and localization of Hydrogen in metals. In this paper, a damaged boiler tube made of grade 20 - St.20 (or 20G, equivalent to AISI 1020) was investigated. The experimental research was conducted in two distinctive phases: failure analysis of the boiler evaporator tube sample and subsequent postmortem analysis of the viable Hydrogen embrittlement mechanisms (HE) in St.20 steel. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature Hydrogen Attack (HTHA) during service, as a result of the development of Hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, tube wall thickness measurement, tensile testing, hardness measurement, impact strength testing (on instrumented Charpy machine), analysis of the chemical composition of corrosion products - deposit and the microstructural characterization by optical and scanning electron microscopy - SEM/EDX. The HTHA damage mechanism is a primary cause of boiler tube fracture. Based on the multi-scale special model, applied in subsequent postmortem investigations, the results indicate a simultaneous action of the Hydrogen-enhanced decohesion (HEDE) and Hydrogen-enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of Hydrogen in investigated steel. The model is based on the correlation of mechanical properties to the SEM fractography analysis of fracture surfaces.
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Hydrogen Embrittlement of Low Carbon Structural Steel
Procedia Materials Science, 2014Co-Authors: Milos B. Djukic, Gordana M. Bakic, Vera Sijacki Zeravcic, Aleksandar Sedmak, Bratislav RajicicAbstract:Hydrogen embrittlement (HE) of steels is extremely interesting topic in many industrial applications, while a predictive physical model still does not exist. A number of studies carried out in the world are unambiguous confirmation of that statement. Bearing in mind multiple effects of Hydrogen in certain metals, the specific mechanism of Hydrogen embrittlement is manifested, depending on the experimental conditions. In this paper structural, low carbon steel, for pressure purposes, grade 20 -St.20 (GOST 1050-88) was investigated. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature Hydrogen Attack and HE during service, as a result of the development of Hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, hardness measurement, impact strength testing (on instrumented Charpy machine) and microstructural characterization by optical and scanning electron microscopy -SEM/EDX. Based on multi-scale special approach, applied in experimental investigations, the results, presented in this paper, indicate the simultaneous action of the Hydrogen-enhanced decohesion (HEDE) and Hydrogen enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of Hydrogen in investigated steel. These results are consistent with some models proposed in literature, about a possible simultaneous action of the HELP and HEDE mechanisms in metallic materials.
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20th European Conference on Fracture (ECF20) Hydrogen embrittlement of low carbon structural steel
2014Co-Authors: Milos B. Djukic, Vera Sijacki Zeravcic, Aleksandar Sedmak, Gordana Bakić, Bratislav RajicicAbstract:Abstract Hydrogen embrittlement (HE) of steels is extremely interesting topic in many industrial applications, while a predictive physical model still does not exist. A number of studies carried out in the world are unambiguous confirmation of that statement. Bearing in mind multiple effects of Hydrogen in certain metals, the specific mechanism of Hydrogen embrittlement is manifested, depending on the experimental conditions. In this paper structural, low carbon steel, for pressure purposes, grade 20 - St.20 (GOST 1050-88) was investigated. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature Hydrogen Attack and HE during service, as a result of the development of Hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, hardness measurement, impact strength testing (on instrumented Charpy machine) and microstructural characterization by optical and scanning electron microscopy - SEM/EDX. Based on multi-scale special approach, applied in experimental investigations, the results, presented in this paper, indicate the simultaneous action of the Hydrogen-enhanced decohesion (HEDE) and Hydrogen enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of Hydrogen in investigated steel. These results are consistent with some models proposed in literature, about a possible simultaneous action of the HELP and HEDE mechanisms in metallic materials. © 2014 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of the Norwegian University of Science and Technology (NTNU), Department of Structural Engineering .
Frederic Cegla - One of the best experts on this subject based on the ideXlab platform.
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Reconstruction of Temperature Distribution in a Steel Block Using an Ultrasonic Sensor Array
Journal of Nondestructive Evaluation, 2014Co-Authors: A. Gajdacsi, A. J. C. Jarvis, P. Huthwaite, Frederic CeglaAbstract:Permanently installed ultrasonic sensors have the capability of measuring much smaller changes in the signal than conventional sensors that are used for ultrasonic inspections. This is because uncertainties associated with coupling fluids and positional offsets are eliminated. Therefore it is potentially possible to monitor the onset of material degradation. A particular degradation mechanism that we are keen to monitor is high temperature Hydrogen Attack; where the amount of damage is linked to a drop in ultrasonic velocity which we hope can be monitored for with an ultrasonic array. The changes introduced in the ultrasonic propagation velocity are expected to be of the order of 1 % and in practice they are observable only from a very limited field of view (i.e. from the outside of a pipe) and therefore the reconstruction is challenging to accomplish. In order to explore the feasibility of this, we are investigating the reconstruction of a non-uniform temperature distribution which allows us to quickly evaluate the sensitivity of our method to small spatial variations in ultrasonic velocity of the material. Two reconstruction algorithms were implemented and their performance compared in simulated and real measurements. The results of the tests were encouraging: local temperature differences as low as $$10~{^\circ }$$ 10 ∘ C could be detected, which corresponds to a local propagation velocity change of $$5$$ 5 m/s ( $$0.15~\%$$ 0.15 % relative velocity change).
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Reconstruction of temperature distribution in a steel block using an ultrasonic sensor array
2013Co-Authors: A. Gajdacsi, A. J. C. Jarvis, Frederic CeglaAbstract:The variability of conventional sensors used for ultrasonic inspections can be greatly reduced by permanently installing them, therefore eliminating uncertainties caused by positional variations and coupling fluids. Much smaller changes are measurable and so the monitoring of the onset of material degradation becomes feasible. One of the typical degradation mechanisms affecting the petrochemical industry is high temperature Hydrogen Attack, which involves Hydrogen diffusing into the material at high partial pressures and forming methane voids by reaction with the carbon in the steel. These methane voids cause a small drop in ultrasonic velocity which it is hoped can be monitored for with an ultrasonic array. The accuracy of reconstructing a non-uniform ultrasonic propagation velocity distribution is vital therefore and is investigated by applying heat to the specimen to replicate the effects of material degradation. A number of proposed reconstruction algorithms are compared both for simulated and real ex...
Petros Athanasios Sofronis - One of the best experts on this subject based on the ideXlab platform.
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A microstructure-based mechanism of cracking in high temperature Hydrogen Attack
Acta Materialia, 2017Co-Authors: May L. Martin, Mohsen Dadfarnia, S. Orwig, D. Moore, Petros Athanasios SofronisAbstract:Abstract High Temperature Hydrogen Attack (HTHA) of steels plagues higher temperature industrial applications, especially in the petrochemical industry, due to the lack of a mechanistic understanding of the phenomenon and the use of empirically established design criteria, such as the Nelson curves. By using advanced microscopy techniques to explore the microstructure immediately ahead of crack tips and along cavitated grain boundaries, we gained a better understanding of the physical processes occurring early during the HTHA damage process, which can guide the development of models for the degradation process accounting for methane formation and creep cavitation. The results confirm the fundamentals of previously proposed models, but also provide finer details than have been previously known. Based on the underlying deformation and grain boundary fracture, we propose a model for material failure underlying HTHA.
May L. Martin - One of the best experts on this subject based on the ideXlab platform.
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A model for high temperature Hydrogen Attack in carbon steels under constrained void growth
International Journal of Fracture, 2019Co-Authors: Mohsen Dadfarnia, May L. Martin, David E. Moore, Steve E. Orwig, Petros SofronisAbstract:Petrochemical vessels exposed to high temperature and high pressure Hydrogen gas may suffer from high temperature Hydrogen Attack (HTHA). HTHA is a Hydrogen-induced degradation of carbon steels whereby internal Hydrogen reacting with carbides forms methane gas bubbles, mainly on grain boundaries (GBs), with an associated loss in strength that can result in premature fracture of structural components. The design of equipment against HTHA is primarily based on the use of the empirical Nelson curves which are phenomenological and do not account for the underlying failure mechanisms and the material microstructure. Starting from the underlying deformation and fracture mechanisms, we present a simple constraint-based model for failure of steels by HTHA which involves growth of GB voids due to coupled diffusion of atoms along the GBs and creep of the matrix surrounding the voids. Since voids form only on some of the GBs, the uncavitated GBs geometrically constrain the growth of voids on the cavitated ones. The model is used to study void growth in HTHA of 21/4Cr–1Mo steel both in the presence and absence of externally applied stress. In the latter case, the model predictions are in good agreement with experimental results. Lastly, the model is used to develop a Nelson-curve type diagram in the presence of external stress in which the curves demarcating the safe/no-safe regimes are functions of the time to failure. This diagram though should be viewed as the result of the application of a new methodology toward devising mechanism-based Nelson curves and not as proposed new Nelson curves for the steel under investigation.
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A microstructure-based mechanism of cracking in high temperature Hydrogen Attack
Acta Materialia, 2017Co-Authors: May L. Martin, Mohsen Dadfarnia, S. Orwig, D. Moore, Petros Athanasios SofronisAbstract:Abstract High Temperature Hydrogen Attack (HTHA) of steels plagues higher temperature industrial applications, especially in the petrochemical industry, due to the lack of a mechanistic understanding of the phenomenon and the use of empirically established design criteria, such as the Nelson curves. By using advanced microscopy techniques to explore the microstructure immediately ahead of crack tips and along cavitated grain boundaries, we gained a better understanding of the physical processes occurring early during the HTHA damage process, which can guide the development of models for the degradation process accounting for methane formation and creep cavitation. The results confirm the fundamentals of previously proposed models, but also provide finer details than have been previously known. Based on the underlying deformation and grain boundary fracture, we propose a model for material failure underlying HTHA.