Computational component analysis techniques for high temperature power plant applications

There is a trend in the power industry for high temperature components (such as steam pipe work) to be operated in an increasingly arduous fashion. This would involve the use of elevated steam temperatures/pressures and a greater frequency of start up/shut down cycles. Such generation strategies are being adopted due to the need for thermally efficient power supply that can match fluctuating market demands. If these generation strategies are to be implemented safely it is critical that careful analysis of the system components is conducted in order to ensure that premature failure does not occur. The advanced material models and techniques that are used in academia to simulate these components are often out of reach of the engineers working in industry. The present work describes the development of an analysis “toolbox” that takes several advanced material models (which can accommodate complex loading conditions) and applies them in numerical (finite element analysis, FEA) and approximate life estimation methods. The toolbox comprises several modules, each of which relates to a specific aspect of component analysis. In this thesis, the fundamental procedures behind these modules are developed in novel ways in addition to the development of the toolbox as a whole. The toolbox modules may be roughly divided into the definition of a component’s material, geometry and loading condition, followed by some form of analysis procedure and a report of the key results. A material’s behaviour is commonly determined from mechanical tests. For in service components, scoop sampling is an exciting new method to extract small amounts of material which may then be tested using several novel small specimen techniques. An investigation has been conduced in the present work that verifies the safety of this method and allows the localised stress behaviour around an excavation to be estimated. Material constants in material behaviour models are usually determined by fitting the outputs of the model to experimental data in an optimisation procedure. A great deal of work has been completed on this topic using the complex Chaboche unified visco-plasticity model. This has led to the formation of the combined parallel optimisation strategy and the development of data cleaning for the determination of material constants in any model. Due to the high temperature conditions power plant components operate in, creep is a major concern. Several damage material models have been compared which can represent failure due to creep. Generally, these models can be divided into power law and hyperbolic sine functions. Through a comparative investigation using multiple component geometries, it has been found that the hyperbolic sine function creep law gives lower predictions of failure time than the power law models at realistic stress levels. Hyperbolic sine function failure lives were also more representative of reality. It is therefore critical when performing component analysis to consider the form of a material model as well as the loading range its material constants are applicable to. The Chaboche unified visco-plasticity model has also been discussed. Using this model, both hardening due to the accumulation of plastic strain and viscous effects (such as creep stress relaxation) may be described. Models like this will play an important role in the analysis of high temperature components as they experience fluctuations in both load and temperature. Although it appears simple, the geometry of a high temperature pipe bend in a power plant is actually complex due to the manufacturing process employed (a straight pipe section is heated through induction coils and bent using a fixed radius arm). The pipe’s wall thickness not only varies circumferentially around the pipe’s cross section but also around the bend itself. Through the analysis of industrial data (collected by ultrasonic measurement of components during outage inspections) several novel geometry factors have been developed that quantify this dimension variation. A new method to analyse such pipe bends has also been created that interpolates the stress states between two dimensional (2D) models that represent the cross section of a pipe bend at several key locations. Once a geometry, loading condition and material has been defined, an analysis procedure may be employed in order to assess the condition of the component. As creep is a key concern under high temperature conditions, most of the analysis procedures discussed in the present work are focused on the prediction of peak rupture stresses (δR) which may be used to estimate failure lives due to creep. Several approximate (errors are typically less than 5%) parametric relationships have been developed that allow peak rupture stresses to be determined based on, for example, pipe bend geometry factors. In addition, to aid in bespoke FEA analyses, a collection of routines with a graphical user interface (GUI) have been created that can write input files for a commercial FEA code (ABAQUS), run the job and post process the results. This can save a great amount of user effort when attempting to analyse components. Finally, an original neural network (that uses a partially connected, multiple input node architecture) has been proposed that predicts δR in pipe bends operating under steady-state creep conditions. Both internal pressure and system loads have been incorporated as inputs for this neural network. This has required the definition of several new load factors that describe the system loads acting on a component. Recommendations for future developments based on this research have also been given. Future developments may look to include fatigue effects in parametric equations, as well as considering the effect of varying loading conditions (possibly through a damage fraction approach). The Chaboche model (or similar unified model) may be modified to include temperature dependency and damage effects (allowing for a wider application to component analysis). The effect of geometry variation may be included in the neural network, again extending its applicability, and stresses due to temperature distributions in the piping components may be incorporated (at present, these have not been considered, however system loads may be thermally driven). The work presented in this thesis addresses a complete analysis procedure, from collecting material information from a component through scoop sampling, to determining material constants for this material by an optimisation procedure and analysing the component using either numerical or approximate methods. Although pipe bends have been considered for the significant part of this work due to the relatively small amount of research reported in literature, similar methodologies may be applied to other power plant components of interest, such as welds, steam headers or branch pipes

Computational component analysis techniques for high temperature power plant applications

There is a trend in the power industry for high temperature components (such as steam pipe work) to be operated in an increasingly arduous fashion. This would involve the use of elevated steam temperatures/pressures and a greater frequency of start up/shut down cycles. Such generation strategies are being adopted due to the need for thermally efficient power supply that can match fluctuating market demands. If these generation strategies are to be implemented safely it is critical that careful analysis of the system components is conducted in order to ensure that premature failure does not occur. The advanced material models and techniques that are used in academia to simulate these components are often out of reach of the engineers working in industry. The present work describes the development of an analysis “toolbox” that takes several advanced material models (which can accommodate complex loading conditions) and applies them in numerical (finite element analysis, FEA) and approximate life estimation methods. The toolbox comprises several modules, each of which relates to a specific aspect of component analysis. In this thesis, the fundamental procedures behind these modules are developed in novel ways in addition to the development of the toolbox as a whole. The toolbox modules may be roughly divided into the definition of a component’s material, geometry and loading condition, followed by some form of analysis procedure and a report of the key results. A material’s behaviour is commonly determined from mechanical tests. For in service components, scoop sampling is an exciting new method to extract small amounts of material which may then be tested using several novel small specimen techniques. An investigation has been conduced in the present work that verifies the safety of this method and allows the localised stress behaviour around an excavation to be estimated. Material constants in material behaviour models are usually determined by fitting the outputs of the model to experimental data in an optimisation procedure. A great deal of work has been completed on this topic using the complex Chaboche unified visco-plasticity model. This has led to the formation of the combined parallel optimisation strategy and the development of data cleaning for the determination of material constants in any model. Due to the high temperature conditions power plant components operate in, creep is a major concern. Several damage material models have been compared which can represent failure due to creep. Generally, these models can be divided into power law and hyperbolic sine functions. Through a comparative investigation using multiple component geometries, it has been found that the hyperbolic sine function creep law gives lower predictions of failure time than the power law models at realistic stress levels. Hyperbolic sine function failure lives were also more representative of reality. It is therefore critical when performing component analysis to consider the form of a material model as well as the loading range its material constants are applicable to. The Chaboche unified visco-plasticity model has also been discussed. Using this model, both hardening due to the accumulation of plastic strain and viscous effects (such as creep stress relaxation) may be described. Models like this will play an important role in the analysis of high temperature components as they experience fluctuations in both load and temperature. Although it appears simple, the geometry of a high temperature pipe bend in a power plant is actually complex due to the manufacturing process employed (a straight pipe section is heated through induction coils and bent using a fixed radius arm). The pipe’s wall thickness not only varies circumferentially around the pipe’s cross section but also around the bend itself. Through the analysis of industrial data (collected by ultrasonic measurement of components during outage inspections) several novel geometry factors have been developed that quantify this dimension variation. A new method to analyse such pipe bends has also been created that interpolates the stress states between two dimensional (2D) models that represent the cross section of a pipe bend at several key locations. Once a geometry, loading condition and material has been defined, an analysis procedure may be employed in order to assess the condition of the component. As creep is a key concern under high temperature conditions, most of the analysis procedures discussed in the present work are focused on the prediction of peak rupture stresses (δR) which may be used to estimate failure lives due to creep. Several approximate (errors are typically less than 5%) parametric relationships have been developed that allow peak rupture stresses to be determined based on, for example, pipe bend geometry factors. In addition, to aid in bespoke FEA analyses, a collection of routines with a graphical user interface (GUI) have been created that can write input files for a commercial FEA code (ABAQUS), run the job and post process the results. This can save a great amount of user effort when attempting to analyse components. Finally, an original neural network (that uses a partially connected, multiple input node architecture) has been proposed that predicts δR in pipe bends operating under steady-state creep conditions. Both internal pressure and system loads have been incorporated as inputs for this neural network. This has required the definition of several new load factors that describe the system loads acting on a component. Recommendations for future developments based on this research have also been given. Future developments may look to include fatigue effects in parametric equations, as well as considering the effect of varying loading conditions (possibly through a damage fraction approach). The Chaboche model (or similar unified model) may be modified to include temperature dependency and damage effects (allowing for a wider application to component analysis). The effect of geometry variation may be included in the neural network, again extending its applicability, and stresses due to temperature distributions in the piping components may be incorporated (at present, these have not been considered, however system loads may be thermally driven). The work presented in this thesis addresses a complete analysis procedure, from collecting material information from a component through scoop sampling, to determining material constants for this material by an optimisation procedure and analysing the component using either numerical or approximate methods. Although pipe bends have been considered for the significant part of this work due to the relatively small amount of research reported in literature, similar methodologies may be applied to other power plant components of interest, such as welds, steam headers or branch pipes

Towards a unified design-by-analysis solution to pressure vessel nozzle-shell junctions under combined loading

The finite element method is the most commonly used modern approach when solving complex practical cylinder-cylinder junctions in pressure vessels. This is used when the geometrical arrangement is out with the permitted scope of the design-by-rule approaches or when detailed stress information is required as in a fatigue assessment. High-stress concentrations occur on the crotch corner for cylinder-cylinder joints, and it is possible to reach solutions for this problem by using both theoretical and numerical solutions. However, those approaches do not fully overlap nor have the same underlying assumptions. As such, an innovative high-fidelity finite element model has been developed to provide a holistic unified approach which can tackle a wide range of problems. In this study, various detailed nozzle design challenges were investigated including single and multiple nozzle combinations, nozzle-cylinder systems with different size ratios, oblique nozzles combinations, fillet weld applications, pad reinforcements, stress linearization, external loading cases, limit loads, and cyclic loads. In addition, elastic, elastic - perfectly plastic, full plastic and fracture analysis were performed. Stress intensity factors are obtained with the results of finite element analysis for various internal pressure and external loading conditions, and an attachment parameter and design curves are proposed. Finally, the Multiple Plastic Slope method, which is an alternative to TI and TES methods, which can be applied more practically and can make a more conservative plastic limit load estimation, has been proposed.The finite element method is the most commonly used modern approach when solving complex practical cylinder-cylinder junctions in pressure vessels. This is used when the geometrical arrangement is out with the permitted scope of the design-by-rule approaches or when detailed stress information is required as in a fatigue assessment. High-stress concentrations occur on the crotch corner for cylinder-cylinder joints, and it is possible to reach solutions for this problem by using both theoretical and numerical solutions. However, those approaches do not fully overlap nor have the same underlying assumptions. As such, an innovative high-fidelity finite element model has been developed to provide a holistic unified approach which can tackle a wide range of problems. In this study, various detailed nozzle design challenges were investigated including single and multiple nozzle combinations, nozzle-cylinder systems with different size ratios, oblique nozzles combinations, fillet weld applications, pad reinforcements, stress linearization, external loading cases, limit loads, and cyclic loads. In addition, elastic, elastic - perfectly plastic, full plastic and fracture analysis were performed. Stress intensity factors are obtained with the results of finite element analysis for various internal pressure and external loading conditions, and an attachment parameter and design curves are proposed. Finally, the Multiple Plastic Slope method, which is an alternative to TI and TES methods, which can be applied more practically and can make a more conservative plastic limit load estimation, has been proposed

Design, organization and implementation of a methods pool and an application systematics for condition based maintenance

Zunehmender Wettbewerb in der Industrie erfordert immer kürzere Amortisationszeiten von kapitalintensiven Produktionsanlangen. Wesentliche Voraussetzungen für die Realisierung kurzer Amortisationszeiträume sind eine hohe Verfügbarkeit der Anlagen und das Erreichen einer gleichmäßig hohen und konstanten Produktqualität. Eine effiziente Instandhaltungsstrategie unterstützt diese Anforderungen an die Verfügbarkeit und an die Produktqualität, vor allem durch eine geringe Bedarfswartung und zunehmend vorbeugende Instandhaltungsbemühungen. In der Industrie wird hierzu häufig die zustandsbasierte Instandhaltung (Condition Based Maintenance - CBM) angewendet. Die CBM Methode versucht aus Zustandseinschätzung der Maschinen, abgeleitet von verschiedenen Zustandsüberwachungs-Verfahren (Condition Monitoring Technique - CMT) und zerstörungsfreien Prüfungen (Nondestructive Test - NDT), erste Mängel zu identifizieren, bevor sie sich kritisch auf die Produktion auswirken. Ein effektives CBM Programm verlangt eine frühe Fehlererkennung und eine genaue Identifikation der Fehlerattribute. Diese Anforderungen werden in der Industrie heute noch unzureichend erfüllt. Die Ursache liegt vor allem in den hohen Kosten, die sich aufgrund unzureichender Information über die potenziellen Fehler ergeben, sowie in der unzulänglichen Kenntnis oder ungeeigneten Anwendung von verschiedenem CMTs und NDTs begründet. Daher werden im Rahmen dieser Arbeit eine neuartige Toolbox und ein Anwendungskonzept entwickelt, um die Umsetzung eines effektiven CBM Programms in der Automobil-Zulieferindustrie zu unterstützen. Hierbei ist der Ansatz so allgemein gewählt, dass er nicht nur auf das Anwendungsgebiet der Automobilindustrie beschränkt ist, sondern auch auf die allgemeine Herstellungs- oder Produktionsindustrie angewendet werden kann. Die CBM-Toolbox setzt sich aus drei Hauptwerkzeugen zusammen. Das erste Werkzeug fasst statistische Fehler-Analysen zusammen, die die in einem Informationssystem des Betriebes vorhandenen Fehlerdaten auswertet, um die relevanten Informationen tabellarisch bzw. grafisch darzustellen. Das zweite Werkzeug ist eine Wissensdatenbank in der das Expertenwissen über verschiedene CMTs und NDTs verwaltet wird. Dieses Expertenwissen ist so strukturiert, dass zusätzlich zu jeder Methode, ihre Anwendbarkeit, Nachweisbarkeit und Vorteile bzw. Nachteile dargestellt werden. Das dritte Werkzeug ist eine objektbasierte Problem-und-Ursache-Analyse, deren Ergebnis eine tabellarisch dargestellte Problem-Ursache Beziehung von besonderen Maschinenanlagen ist. Diese Hauptwerkzeuge werden durch zwei weitere Werkzeuge, ein Finanzanalyse-Werkzeug und eine Auswahlmatrix ergänzt, die die verschiedenen Entscheidungsmöglichkeiten hinsichtlich der Umsetzbarkeit bewertet.The everyday increasing competition in industry and the compulsion of faster investment paybacks for complex and expensive machinery, in addition to operational safety, health and environmental requirements, take for granted high availability of the production machinery and high and stable quality of products. These targets are reached only if the machinery is kept in proper working condition by utilizing an appropriate maintenance tactic. In this frame of thought, monitoring of machinery systems has become progressively more important in meeting the rapidly changing maintenance requirements of today’s manufacturing systems. Besides, as the pressure to reduce manning in plants increases, so does the need for additional automation and reduced organizational level maintenance. Augmented automation in manufacturing plants has led to rapid growth in the number of machinery sensors installed. Along with reduced manning, increased operating tempos are requiring maintenance providers to make repairs faster and ensure that equipment operates reliably for longer periods. To deal with these challenges, condition based maintenance (CBM) has been widely employed within industry. CBM, as a preventive and predictive action, strives to identify incipient faults before they become critical through structural condition assessment derived from Different condition monitoring techniques (CMT) and nondestructive tests (NDT). An effective CBM program requires early recognition of failures and accurate identification of the associated attributes in a feasible manner. The achievement of this proficiency in industry is still intricate and relatively expensive due to deficient information about the potential failures as well as inadequate knowledge or improper application of different CMTs and NDTs. Accordingly, a new toolbox has been developed to facilitate and sustain effective CBM programs in the automotive supply industry. The CBM toolbox is consisted of three major tools. The first tool is a series of statistical failure analyses which uses the failure history data available in a plant’s information system to generate valuable information in tabulated and graphical postures. The second tool is a repository filled with expert knowledge about different CMTs and NDTs formatted in a way that in addition to the concept of each technique, its applicability, detectability, and its pros and cons are expressed. The third tool is an object based problem and cause analysis whose outcome is tabulated problem-cause relationships associated with particular machinery objects. These major tools are also accompanied by two supplementary tools, a financial analysis tool and a selection matrix, to ensure feasibility of all undertaken decisions while using the toolbox

Second Aerospace Environmental Technology Conference

The mandated elimination of CFC'S, Halons, TCA, and other ozone depleting chemicals and specific hazardous materials has required changes and new developments in aerospace materials and processes. The aerospace industry has been involved for several years in providing product substitutions, redesigning entire production processes, and developing new materials that minimize or eliminate damage to the environment. These activities emphasize replacement cleaning solvents and their application, verification, compliant coatings including corrosion protection system and removal techniques, chemical propulsion effects on the environment, and the initiation of modifications to relevant processing and manufacturing specifications and standards