Diss. Teknillinen korkeakoulu, 2006. / Myös verkkojulkaisuna.

Call number: LD2668 .T4 1964 D44 / Master of Science

Call number: LD2668 .T4 1965 K21 / Master of Science

ABSTRACT This work deals with the damage due to the simultaneous presence of hydrogen in atomic form and stress – straining. The aim of this work is twofold: to better understand the hydrogen embrittlement mechanisms and to translate the acquired knowledge into a more appropriate qualification test. The phenomena of hydrogen entry and transport inside the metals, together with the different types of damages due to the presence of hydrogen, are presented. The analysis of the most important models proposed up to now for hydrogen embrittlement (HE) indicated that the slow dynamic plastic straining is a key factor for the embritteling process. There is a synergistic effect of hydrogen – dislocations interactions: on one hand hydrogen facilitates the dislocations movement (according to the HELP mechanism) and on the other hand dislocations transport hydrogen during their movement when their velocity is lower than a critical value. This work is focused on supermartensitic stainless steels, base and welded materials. The interest on these materials is due to their broad use in offshore oil production. First, the material’s characterisation with regards to hydrogen content and localisation was performed. This was conducted in charging conditions that are representative of industrial applications. Because of previous industrial experience it was necessary to find a more appropriate qualification test method to asses the risk of HE. In this work we proposed the stepwise repeated slow strain rate test (SW R – SSRT) as a qualification test method for supermartensitic stainless steels. This test method combines hydrogen charging, test duration, plastic, dynamic and slow strains. Thus, this test method is coherent with both the model HELP proposed for hydrogen embrittlement and the observations of industrial failures. The stepwise repeated slow strain rate test (SW RSSRT) is interesting not only as a qualification test of martensitic stainless steels, but also as a qualification test of conditions for using these materials (type of straining, range of strain and stress, strain rate, hydrogen charging conditions, etc.). RESUME Ce travail se rapporte à l’endommagement provoqué par la présence simultanée de l’hydrogène sous forme atomique et une contrainte (appliquée où résiduelle). Ce travail a comme but une meilleure compréhension du mécanisme de la fragilisation par l’hydrogène (FPH) et la recherche d’un essai de qualification qui soit cohérent avec ce mécanisme. Les phénomènes liés à l’entrée et au transport de l’hydrogène au sein des métaux, ensemble avec les différents types d’endommagements dus à la présence de l’hydrogène, sont présentés. L’analyse des modèles proposés jusqu’au présent pour la fragilisation par l’hydrogène (FPH) suggère que la déformation lente plastique dynamique est le facteur clé pour le processus de la fragilisation. Il y a un effet synergétique des interactions entre l’hydrogène et les dislocations: d’un coté l’hydrogène facilite le mouvement des dislocations (d’après le modèle HELP) et d’un autre coté les dislocations transportent l’hydrogène pendant leur mouvement, pourvu que leur vitesse soit en dessous d’une valeur critique. Le travail a été conduit sur des aciers supermartensitiques, matériau de base et soudé. L’intérêt pour ces matériaux réside de leur large utilisation dans la production du pétrole en offshore. D’abord, le matériau a été caractérisé du point de vu de la teneur et de la localisation de l’hydrogène. Les essais ont été conduits dans des conditions représentatives pour les cas industriels. L’expérience industrielle d’auparavant indique qu’il est nécessaire de trouver un test de qualification plus approprié pour estimer la susceptibilité à la fragilisation par l’hydrogène. Dans ce travail on propose un essai de traction lente incrémentée (SW R – SSRT) comme méthode de qualification pour les aciers supermartensitiques. L’essai combine le chargement en hydrogène, la durée d’essai, la déformation lente, plastique et dynamique. Donc, cette méthode d’essai est cohérente avec le modèle HELP proposé pour FPH et les observations des accidents industriels. Cet essai est intéressant pas seulement comme essai de qualification pour les aciers supermartensitiques, mais aussi comme essai de qualification pour les conditions d’utilisation des ces matériaux (type de déformation, niveau de déformation et contrainte, vitesse de déformation, conditions de chargement en hydrogène, etc.).

No description available.

Systematic pre cleaning, disinfection and sterilization of medical equipment used in examination and treatment of patients are very important for safe care of the patients and the staff handling these instruments. Due to the technical properties of stainless steel, its hygienic experience and the sophisticated look of the stainless steel, it has dominated the medical health care environments for decades. The wetting properties of stainless steel surfaces are presumed to be essential for the process of clean ability and for a wide variety of bio compatibility.In collaboration with the topical company for this thesis, the idea is to find the correlation between the surface properties of various stainless steel in relation to their wetting and spreading ability to enable efficient cleaning of the surface. For a substrate surface to be thoroughly cleaned of any debris or soil, it should be able to allow proper adherence of the liquid across its surface to a certain degree good enough to ensure good wettability of the surface and conversely easy and proper removal of any attached soil on the surface. Higher demand on cleaning, disinfection and sterilization processes became more and more pressing due the development of complex medical equipment.Different stainless steel (316L) surface finishes and some surgical equipment are investigated using the state of the equipment at Halmstad University. Using the imaging interferometer and mapping software, Mountain Map, the results obtained is controlled readings and classification of the various surface parameters. Contact angle measurements were carried out on each surface with three polar (Distilled water, Glycerol and Ethylene glycol) and one non polar (Olive Oil) probe liquids with a drop volume of 3μm using Theta Optical Tensiometer and One Attention Software for the analysis. The impact and correlations of the surface parameters on wettability was later compared from the measurements obtained.

Thermal transport behavior of austenite stainless steel stripe (304) and the carbon nano-tubes (CNTs) films of varying thickness are studied using a micropipette thermal sensor. Micropipette sensors of various tip sizes were fabricated and tested for the sensitivity and reliability. The sensitivity deviated by 0.11 for a batch of pipette coated under same physical vapor deposition (PVD) setting without being affected by a tip size. Annealing, rubber coating and the vertical landing test of the pipette sensor proved to be promising in increasing the reliability and durability of the pipette sensors. A micro stripe (80µm × 6µm × 0.6µm) of stainless steel, fabricated using focused ion beam (FIB) machining, was characterized whose thermal conductivity was determined to be 14.9 W/m-K at room temperature. Similarly, the thermal characterization of CNT films showed the decreasing tendency in the thermal transport behavior with the increase in the film thickness.

Analysis of corrosion in marine and acid environments is a complicated task, involving the interaction of thermodynamic, kinetic and geometrical factors. Two mathematical models which predict corrosion behaviour have been implemented for personal computers. The first program uses an assumption of unidirectional current flow to simplify the prediction of potential distributions for systems of essentially cylindrical geometry containing natural seawater-based electrolytes of differing strength. Using experimentally determined electrochemical and flow rig data, experimental and theoretical results were compared. The correlation between the two was shown to be poor, and this is attributed to the unrepresentative nature of the electrochemical data input to the model. The second model involves the synthesis of polarization curves. Several algorithms to model passivating behaviour have been studied, and one was selected and incorporated into the calculation routine. A number of kinetic and thermodynamic parameters are used in algorithms describing such behaviour, along with activation, concentration and solution polarization effects, for a number of redox reactions, which are then combined to produce an overall potential-log current density curve. Experimentally determined data for pure iron and different stainless steels in marine and acid environments of differing dissolved oxygen content and temperature were obtained. Theoretical models were constructed for each system, and compared to experimental data. Excellent correlation between experimental and theoretical data was obtained for potential ranges in excess of 2 V. Trends in parameter values were discussed, and compared to published data. The transition between stable and unstable passivity of stainless steels was shown to be dependent on the oxygen reduction diffusion limited current density and the iron dissolution reaction free corrosion current density, which in turn was linked to the dissolved oxygen content and temperature of the electrolyte. A new model for the behaviour of stainless steels in the transpassive region was proposed.

Este trabalho foi desenvolvido com o intuito principal de adquirir \"know how\" na fabricação de componentes fundidos e usinados de bombas centrífugas, para aplicações em plataformas \"offshore\". Os materiais utilizados para esse destino - aços inoxidáveis super duplex - constituem sistemas termodinamicamente meta estáveis, que buscam o estado de estabilidade termodinâmica quando excitados termicamente. Por outro lado, esses materiais apresentam uma grande instabilidade dimensional, devido às tensões residuais desenvolvidas no resfriamento do tratamento térmico e durante o processo de usinagem, principalmente quando se trabalha com tolerâncias extremamente pequenas (10 m a 15 μm). Nesse contexto, foram realizados tratamentos térmicos a partir de 520°C, variando-se de 20°C em 20°C até a temperatura limite de 1180°C, com o objetivo de verificar-se a influência dessas temperaturas na microestrutura, dureza e tenacidade ao impacto do material. O enfoque principal foi dado na dinâmica de precipitação da fase sigma, que é o intermetálico mais conhecido e estudado nessa categoria de aços. Sua precipitação é inevitável, durante o processo de solidificação, porém, pode ser minimizada controlando-se a composição química e a taxa de resfriamento. Partindo-se de uma estrutura solubilizada, foi possível determinar as temperaturas a partir das quais a fase sigma começa a precipitar e dissolve-se por completo, bem como a influência de sua presença na dureza e na energia absorvida no ensaio de impacto Charpy. Técnicas de microscopias óptica, eletrônica de varredura, eletrônica de transmissão e difração de raios-x foram utilizadas para caracterização microestrutural do material nas várias condições de tratamento térmico. Ensaios eletroquímicos utilizando-se água do mar sintética, aerada e saturada com C02, contendo 20000ppm, 40000ppm e 80000ppm de íons cloreto, a temperaturas de 5OC, 25OC e 60°C foram realizados somente para o material solubilizado a 1130°C, 1160°C e solubilizado a 1130°C, seguido por alívio de tensões a 520°C. Os resultados mostraram que o tratamento térmico de alivio de tensões a 520°C, não promoveu precipitação de fases intermetálicas na microestrutura e tampouco prejudicou a resistência a corrosão do material, indicando a possibilidade prática de seu uso. / The present work was developed to acquire know how in manufacturing of castings and machined components for centrifugal pumps for offshore platform applications. Normally, the materials used to do them are the super duplex stainless steels that are thermodynamically metastable systems which tend to equilibrium when thermally activated. On the other hand, these materials show a great dimensional instability due to the residual stresses developed during the cooling from heat treatment process and also after machining process. This is crucial when working with very small dimensional tolerances, typical for these components. It were made stress relief heat treatments from 520°C, increasing the temperatures in 20°C steps until 1180°C to check the influence of these temperatures on microstructures, hardness and absorbed energy in Charpy test of this materials. The main focus was given on sigma phase precipitation dynamic, because it is the most common and studied intermetalic in this kind of stainless steels. It is impossible to avoid its precipitation during the cooling from solidification process, but it can be minimized by controlling the chemical composition and the cooling rate from solidification. Starting with a solution annealed structure, it was possible to determine the temperature where the sigma phase begins to precipitate and also its dissolution temperature. The influence of sigma phase content on hardness and absorbed energy in impact test was evaluated. Microstructure characterization was made using optical, scanning and transmission electron microscopy, as well as X-ray diffraction analysis for each different temperature. The electrochemical corrosion tests using synthetic sea water with 20000ppm, 40000ppm and 80000ppm of chlorine ions, at 5oC, 25°C and 60°C were made. Samples solution annealed such at 1130°C and at 1160°C and solution annealed at 1130°C followed by aging at 520°C were tested electrochemically. The results showed that the stress relief heat treatment at 520°C did not promote the intermetalic phase precipitation on material\'s microstructure and also, did not diminish the material\'s corrosion resistance.

<p>A problem with cold pilgered tubes for OCTG applications is that they can get anisotropic properties with regard to yield strength. One source of anisotropy is texture that is developed during the cold deformation. EBSD measurements have been made on several austenitic stainless steels with different deformations to see what influence the composition has on the texture formation. The same measurements were used to study the influence of grain size on texture formation. The conclusion was that the composition can have an impact on the texture and hence has potential to also affect the anisotropy. The differences in texture cannot be associated with a specific alloying element, but is rather a synergetic effect. It was also concluded that grain structure has no strong influence on texture formation. An evaluation of three different tool designs used for cold pilgering was made. The designs evaluated are referred to as design A, B and C. EBSD measurements showed large deviations in texture in the middle of the wall compared to close to the surface of pilgered OCTG. However, the measurements showed no large differences between the three designs and the texture could not be coupled to the anisotropy.</p>