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Advanced Methods for Damage Evaluation of Boiler Tube Bundles
Naď, Martin ; Odstrčil, Miloslav (referee) ; Jůza, Zdeněk (referee) ; Jegla, Zdeněk (advisor)
This thesis is focused on the application of advanced methods for evaluating damage to boiler tubes, specifically temperature related damage. The aim of this work is to develop an improved damage evaluation procedure utilizing capabilities of modern approaches. This work describes various types of industrial boiler damage. The main focus is on the most exposed and often the most damaged parts of boilers, which are tube bundles (for example, superheaters). Equipment damage is undesirable and often leads to leakages or even to the boiler shutting down. Therefore, it is necessary to find the problem as soon as possible and make the required changes to prevent further damage. The damage types are divided into five categories based on the damage mechanism. Temperature has one of the biggest influences on damage and it may cause short-term or long-term overheating in the tube bundles. This type of damage occurs when the designated temperature is exceeded and results in reduced creep life. It is necessary to know the real surface temperature history of the tube bundle to estimate temperature related damage, however this is often not available. Therefore, it is necessary to calculate those temperatures based on the available data (i.e. inlet and outlet temperatures and pressures). This is real challenge due to the combination of complex flows of the working substances (mainly flue gasses) and heat transfer. Considering available data, new approach is proposed in order to obtain information required for residual creep life estimation. In the first step, thermal – hydraulic calculation is performed followed by a thermal load estimation of a superheater tube bundle in a natural gas fired boiler, using CFD simulations. In the next step, the surface temperature is evaluated and used to determine the temperature related damage, specifically the creep life estimation. The life expectancy is in some ways influenced by imperfections, and therefore at the end of this thesis the influence of the oxide layer on the inner side of tube and fouling on outer side of tube is described.
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Life-Time Management of Process Devices in Industrial Practice
Lošák, Pavel ; Klemeš,, Jiří (referee) ; Ing. Zdeněk Jůza, Ph.D. MBA (referee) ; Vejvoda, Stanislav (advisor)
This dissertation examines life-time management of process and energetic devices in industrial practice, mainly in the area of steam power plants. Furthermore, it focuses on frequent damage mechanisms occurring in this area. It summarizes basics of damaging mechanisms occurring in the process industry area, their monitoring, evaluation and prediction. In the area of steam power plants, the main emphasize was placed on cumulative damage mechanisms. Within the dissertation, mechanisms of creep, fatigue, and their combinations were assessed. Major European standards were examined in order to discuss the amount of contained conservatism and their usability. Subsequently, attention was paid to the methods applicable for creep and fatigue combination evaluation. In the next step life-time monitoring and evaluation standard was discussed. The diagnostic software was created which includes creep, fatigue and creep-fatigue combination evaluation according to valid standards. For online life-time evaluation was proposed refined analytical solution for stress and strain calculation. To further extend the life-time management, the dissertation describes oxide scale damaging together with its evaluation and implementation into diagnostic software. The proposed software is extended by the material module which on the basis of defined materials allows easy and effective usage of material characteristics. For the purpose of refining life-time prediction accuracy, experimental device was schematically described. In addition, the device should be also able to verify used equations. Furthermore, the dissertation includes solution to industrially oriented cases. Firstly, a steam generator with damaged pipes was analyzed, afterwards damaged transferring pipeline. Further analyses deal with U-tube heat exchanger and its damaging. The causes of damage were discovered and corrective measures were proposed. The dissertation concludes with the summarization of potential activities for subsequent research in examined area.
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Stress and strength analysis of steam turbine valve
Kořínek, Tomáš ; Vosynek, Petr (referee) ; Petruška, Jindřich (advisor)
This diploma thesis deals with the determination of lifetime and computational modeling of stress strain states arising in the body of the steam turbine valve. Due to the high temperature of the inlet steam, the creep of the material which fundamentally affects its final lifetime is also considered in the calculation. The lifetime is evaluated by four different procedures using the finite element method via the ANSYS software. The results are compared at the end of this work. One of the chapters is focused on solving the problem of the creep in the ANSYS software environment.
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Particle Polymer Composite in structural details of the building envelope
Dostálová, Darina ; Lavický, Miloš (referee) ; Vokoun,, David (referee) ; Matějka, Libor (advisor)
Due to a European energy concept for reducing energy consumption and also the concept of sustainable development, there is a growing demand for reduced energy consumption during the operation of the building and hence increasing demands on the thermal and mechanical properties of the building envelope. For this reason, it is necessary to look for materials that could meet both thermal and mechanical properties, as well as mechanical resistance and loadability, especially for the application for the foundations of the house, the base of the house and for application to structural details for elimination of the thermal bridges between interior and exterior boundaries. The main motivation for choosing the topic of thesis was to find materials derived from recycled or secondary raw materials that would be suitable for manufacturing composite applicable for structural details in the envelope of the building and for insulating in humid environment. An economic and environmental aspect plays an important role in the choice of material. The main theme of the thesis is the laboratory manufacturing of a composite with a thermoplastic matrix derived from recycled plastic materials and waste foam as a phase. Has been developed a unique Waste-based Particle Polymer Composite (WPPC) made from recycled foam and polypropylene. However, before WPPC can be reliably used by construction designers, physical properties of WPPC must be accurately identified. Therefore, it was designed laboratory manufacturing system and sample testing system, it was studied thermal, mechanical, thermomechanical and moisture absorptivity of WPPC. Application of finished composite material with satisfying thermal insulation properties to structural details to eliminate the thermal bridge, was the next step. These are details of the unloaded, prefabricated balconies, windows, atics, as well as basement constructions and the heel of the central load-bearing wall, the terrain flooring and the staircase wall
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The effective cross-section thickness and its effect on the behavior of concrete constructions
Hofírek, Radovan ; prof. ing. Jan L. Vítek, CSc. (referee) ; Borzovič,, Viktor (referee) ; Zich, Miloš (advisor)
Determination of rheological phenomenon is very difficult, because there are many unknown inputs parameters, e.g. concrete age, the size of elements, relative humidity of the surrounding environment, cement hydration rate, temperature influence, type of strain and treatment. This Ph.D. thesis deals with the effective cross-section thickness and its effect on the behaviour of concrete constructions that is how the rheological phenomena change in time as a result of the application or removal of insulation layer from the concrete surface. Long-term experimental measurements of specimens and real bridge constructions were performed. The data collected from these measurements were described, evaluated and mathematical modifications for the standards Model Code 2010 and Model B4 (B3) have been proposed. Using these new computational formulas is possible to take into consideration the changes in the effective cross-section thickness and therefore make the computational models for concrete structures more accurate.
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Thermal and creep analysis of VVER-1000 reactor pressure vessel at high temperatures caused by fuel melting during severe accident
Gabriel, Dušan ; Gál, P. ; Kotouč, M. ; Dymáček, Petr ; Masák, Jan ; Kopačka, Ján
Thermal and creep analysis of the VVER-1000 reactor pressure vessel (RPV) was performed at high temperatures caused by fuel melting during severe accident. First, the integral code ASTEC was applied simulating severe accident evolution since an initiating event up to a hypothetical radioactive release into the environment. The ASTEC outputs including the remaining RPV wall thickness, the heat flux achieved and the temperature profile in the ablated vessel wall served as boundary conditions for the consequent assessment of RPV integrity carried out with the aid of finite element method (FEM). The FEM analysis was performed including the creep behaviour of RPV material using a complex creep probabilistic exponential model with damage. The objective of the analysis was to computationally assess emergency condition and, on this basis, to propose a general methodology for evaluating the integrity of RPV at high temperatures due to fuel melting during severe accident.
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Influence of severe plastic deformation and subsequent annealing on creep behaviour of martensitic 9% Cr steel
Král, Petr ; Dvořák, Jiří ; Sklenička, Václav ; Horita, Z. ; Tokizawa, Y. ; Tang, Y. ; Kunčická, Lenka ; Kuchařová, Květa ; Kvapilová, Marie ; Svobodová, M.
The objective of the study is to evaluate the effects of severe plastic deformation (SPD) and annealing on creep behaviour of advanced tungsten modified creep-resistant 9 % Cr martensitic P92 steel. The as-received P92 steel was deformed by high-pressure torsion (HTP), high-pressure sliding (HPS) and rotary swaging (RS) at room temperature prior creep testing. These SPD methods imposed significantly different equivalent plastic strain in the range from 1 up to 20. Constant load creep tests in tension were performed in an argon atmosphere at 873 K and applied stress ranging from 50 to 200 MPa. The microstructure and phase composition of P92 steel were studied using a scanning electron microscope Tescan Lyra 3 and a transmission electron microscope Jeol 2100F. The results show that under the same creep loading conditions the HPT and HPS-processed P92 steel exhibited significantly faster minimum creep rates, creep fracture strain and the decrease in the value of the stress exponent of the creep rate in comparison with as-received P92 steel. However, it was revealed that the RS-processed specimens exhibited one order of magnitude lower minimum creep rate and lower ductility compared to commercial P92 steel. The creep curves for the HPT and HPS-processed states exhibited a pronounced minimum of strain rate. The pronounced minimum of strain rate disappeared when these states were annealed at 923K/500h before application of creep loading. The microstructure changes occurring during creep and different creep behaviour between as-received and deformed states are discussed.
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Development and validation of a hypoplastic model for soft clays incorporating rate effects and strength anisotropy
Jerman, Jan ; Mašín, David (advisor) ; Blahůt, Jan (referee) ; Hrubešová, Eva (referee)
The thesis presents modelling framework for soft clays. Soft clays typically occur in marine environment, coastal areas and along rivers, soft clay deposits are also associated with the periglacial conditions. Soft clay seabeds are also prevalent in locations used as foundations of various energy sources (renewable and hydrocarbon). Growing world population increased demand for land, and this, consequently, leads to seaward land reclamation for urban development in coastal areas. Thus, construction on soft soil deposits has become increasingly important as soft clays occur in locations of construction projects for city infrastructure. The stress-strain behaviour of soils, especially clayey soils, is well-known to be rate- dependent. This fact is relevant for specific engineering projects, where the long-term performance of constructions is of interest. This is particularly important for soft clays as the very high degree of compressibility in primary compression and during creep makes rate-dependent soil behaviour an important factor for geotechnical problems. Moreover, the slow slope movements of slow-moving landslides and creeping slopes are controlled mostly by shear creep properties of the shear-zone soil and the effective stress state. Thus, for the case of creeping landslide modelling, a...
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Creep of oak dowel: various loading and environmental conditions
Hasníková, Hana ; Kunecký, Jiří ; Hataj, M.
For research of timber joints, the crucial role in force distribution inside the joint is played by distribution and variability of stiffness of the dowels. Not only the instant stiffness, but the one that we can encounter after some longer period. Also, this value and its statistical distribution is influenced by many other factors, however, humidity and temperature are in timber (oak) dowels of utmost importance. In the work results of a creep experiment made using a special testing rig is presented. It has been found, that biggest changes in creep behavior are in case if very humid conditions are present, and, also, that cycling the temperature in high humidity conditions can produce about 104% of the original instantaneous displacement. The result is not surprising, however, new insights are made thanks to relatively high number of samples and ability to produce some statistics. Another outcome is relation of dowel stiffness in time to the level of applied stress, which is quantified in the article.
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