An investigation of microcrack formation on machined surfaces.

In recent times a number of workers have pointed out the importance of microcrack formation to the machining process and to surface integrity requirements of machined components. Microcracks have been identified within the shear zone and their presence used to explain some aspects of the chip formation process. It is clear that microcracks represent a major feature in the shear zone in machining, particularily when the workpiece is a two-phase material.The presence of microcracks in the machined surface was reported some fifteen years ago and confirmed recently. A preliminary study carried out on a number of materials machined under various cutting conditions has indicated that microcracks are produced in machined surfaces as a result of machining.However, to the present time there has been no systematic study of the formation of microcracks in the machined surface, and their extent, dimensions, and the conditions under which they are produced are completely unknown. In so far as microcracks may affect the fatigue, corrosion and other properties of the machined surface, it is important that a method of quantifying microcrack formation should be found. A feasibility study has been carried out which has led to the use of the transmission electron microscope as a tool to quantify microcrack formation in the machined surface. A technique based on transmission electron microscopy is described in the present thesis along with its application.Two new parameters, the microcrack area ratio "Ma" and the microcrack density "Md" are introduced and defined. The extent of microcrack formation in the machined surface is studied as a result of varying: (i)- cutting speed, (ii)- undeformed chip thickness, (iii)- rake angle, (iv)- workpiece hardness.The results are discussed and conclusions drawn.Finally, a number of suggestions for future work are formulated which mark the start of a whole new area of research in surface microcracking

Etude de l'influence de l'état de surface sur la tenue à la fatigue d'acier XC48

La vie utile d'un matériau en service dépend toujours non seulement de la combinaison des facteurs de charge et d'environnement auxquels il est soumis mais aussi de l'état de surface dont il faut toujours tenir compte dès la mise en service.Cette dépendance est encore plus ressentie dans le cas des composants sollicités à la fatigue. La présente étude vise à établir l'influence des paramètres de surfaces réalisées par tournage sur la résistance à la fatigue d'un acier XC48, en s'attachant plus particulièrement a identifier l'effet de la rugosité qui peut être produite sous différentes conditions d'usinage des surfaces. Pour ce faire, diverses éprouvettes, présentant des combinaisons variées d'état de surfaces, réalisées par tournage à différents paramètres de coupe ont été soumises à des essais de flexion rotative et l'effet sur la durée de vie et la limite de fatigue, pour divers conditions de chargement, a été évalué

Evaluation and Control of the reliability of Weld Joints in Petroleum Products Transportation Pipelines

The economic performance of petroleum products transport companies is dependent on the reliability of their equipment. Ruptures of the weld joints of petroleum products carriage pipelines have major consequences at the human, environmental and economic levels. Weld joints are potential sites of dangerous cracks. The management of reliability of weld joints in pipelines is useful to integrate the quality planning and risks throughout their life cycle and to systematically track their characteristics all along their life cycles. The use in situ of inspection results from non-destructive control techniques is an essential component of evaluation and control of reliability of pipes in their function. It requires calculation methods and tools to assist in the decision-making in support of inspection and repair campaigns. It is in this context that the present study was conducted, which is a contribution to the efforts of methodological assessment of the reliability of petroleum products transport pipelines

Décontraction des assemblages soudés par des traitements thermiques

L'apport de la chaleur lors du soudage notamment le soudage multi-passes est à l'origine de nombreuses transformations métallurgiques. Dans certains cas, ces transformations induisent des microstructures complexes qui peuvent présenter une certaine hétérogénéité mécanique et structurale à travers des joints soudés. Encore, des contraintes résiduelles importantes peuvent provenir des phénomènes mécaniques qui accompagnent le soudage et qui se manifestent lors de la mise en service des assemblages soudés, en conséquence, des ruptures brutales graves peuvent être occasionnées [8]. Selon l'importance de ces contraintes, des traitements de décontraction sont donc à prescrire ou non avant la mise en service des joints soudés. Dans ce présent travail, une investigation est faite sur l'évolution des propriétés mécaniques et structurales d'un joint soudé en acier microallié lors des traitements thermiques de relaxation. Dans ce cadre, la microscopie optique et des essais mécaniques de traction, de résilience et de dureté ont été effectués sur des éprouvettes brutes de soudage, et d'autres traitées thermiquement. Les résultats obtenus montrent que des traitements thermiques appropriés provoquent une décontraction du joint soudé qui se traduise par une faible réduction des caractéristiques de traction et une nette amélioration de la résilience sans affecter considérablement la microstructure du matériau. Les caractéristiques mécaniques obtenues après relaxation sont très acceptables pour l'objectif dans lequel ces joints soudées sont utilisés

Analysis of predictive models of oil transportation ducts rehabilitation

The actions of the various phenomena of corrosion, mechanical constraints and others, contribute to the degradation of hydrocarbons transportation ducts. The combinations of th ese phenomena accelerate pipe ageing, and this results in the increase of the frequency of leaks interventions and pipe ruptures. The only way to struggle against the ageing of oil transportation pipelines is the rehabilitation. This will allow the re - serv icing of pipes whose resistance characteristics are degraded. One of the major difficulties, during the conception of a pipeline rehabilitation program, is the determination of the specific sections to rehabilitate. Indeed if there is any real risk not to do enough rehabilitation in the one hand, there is a risk to bad rehabilitation on the other. The decision to continue to maintain, renovate or replace some degraded sections of a pipeline is not an easy task, and requires development of forecasting models that will enable decision - makers to take the right decisions on the middle and long term. In this context, this study is devoted to analysis of problems associated with statistical exploitation of controls and repair files of aged pipes, establishing acti on plans and controlling the ageing of hydrocarbons transportation pipeline

A Dual PSO-Adaptive Mean Shift for Preprocessing Optimization on Degraded Document Images

In the two past decades, solving complex search and optimization problems with bioinspired metaheuristic algorithms has received considerable attention among researchers. In this paper, the image preprocessing is considered as an optimization problem and the PSO (Particle Swarm Optimization) algorithm was been chosen to solve it in order to select the best parameters. The document image preprocessing step is the basis of all other steps in OCR (Optical Character Recognition) system, such as binarization, segmentation, skew correction, layout extraction, textual zones detection and OCR. Without preprocessing, the presence of degradation in the image significantly reduces the performance of these steps. The authors' contribution focuses on the preprocessing of type: smoothing and filtering document images using a new Adaptive Mean Shift algorithm based on the integral image. The local adaptation to the image quality accelerates the conventional smoothing avoiding the preprocessing of homogeneous zones. The authors' goal is to show how PSO algorithm can improve the results quality and the choice of parameters in pre-processing's methods of document images. Comparative studies as well as tests over the existing dataset have been reported to confirm the efficiency of the proposed approach.080

Wear Behavior and Microstructure of Thermally Sprayed NiCrBSiFeC and Composite NiCrBSiFeC-WC(Co) Coatings

International audienceIn this work, a study was carried out on the friction and wear behavior of flame thermal sprayed NiCrBSiFeC-WC(Co) composite and NiCrBSiFeCcoatings subjected to severe wear conditions. For this purpose, flame remelted samples were tested in reciprocating wear conditions based on a cylinder-on-flat configuration. The wear assessment of the coatings was achieved using scanning electron microscopy (SEM)and 3D optical profilometry. The microstructure and the mechanical properties of the coatings were investigated using SEM, EDS and XRDtechniquesas along withindentation tests. The tribological behavior of the substrate and the coatings was successfully studied thankstowear tests conductedon an adapted multi test apparatus. The results show that both NiCrBSiFeC and composite coatings induced a significant increase in the steel substrate hardness and wear resistance due to the formation of precipitates with high hardness well dispersed withinanultra-crystalline structure.Besides, adding WC(Co) to NiCrBSiFeC leads to a composite coating with hardnessandwear resistance further improved. In return, it increases the coefficient of friction (COF) and the coatings’ roughness. Furthermore, improvements in the surface hardness, the roughnessandthe coating-substrate adhesionwere attained after the remelting process for both NiCrBSiFeC and NiCrBSiFeC-WC(Co) coatings. Wear tracks investigations indicated that reciprocating dry sliding based on cylinder-on-flat test configuration promote several wear mechanisms that may occur simultaneously

Fiabilist and economic approaches to optimisation of the renewal of hydrocarbons transporting pipelines

Problems of hydrocarbons transporting pipelines agi ng and rehabilitation are currently a major concern for operators of such installations. Rehabilitating and insuring hydrocarbons transporting pipelines, require interventions, such as the renovation of existing lines, the replacement of some pipelines with new ones, in order to meet the growing demand of consumers and improve the supply reliability. In this context, a decision to repair or replace a section of pipe must co mbine both a technical analysis of failures and sound economic analysis of the choice of possible interventions , which is the purpose of this study, dedicated to research and policy determination of repair and replac ement of aged pipe sections, taking into account the factors mentioned above, and based on significant feedbac

Tensile and torsional loads stress distribution along the drill string for deep wells

Common knowledge and rule of thumb tell us that tensile failures will mostly occur in the pipe body, while torsion failures will occur in the tool joints. The total stresses on the drill string should be considered which are induced by combined bending, torsion and tensile stresses. The latter can usually be operating up until 80 % of the pipe body yield stress, a level which is considered as a safe working limit. Moreover, torque and drag are caused by the lateral forces and the friction between the borehole wall and the drill pipe. The lateral forces depend on the weight of the drill string. Torque and drag are sometimes overlooked when drilling simple wells. In deep well this is not acceptable. Proper decision made using correct torque and drag can make all the difference between TD drilling and suspended drilling. Therefore the over pull load plus the torque are the most important points to be considered in deep well drilling, since the resistance of the drill string body to the combined efforts will probably limit its tensional limit. By this I mean, exerting both a tension and torsion load on the drill string of this later will weaken its yield stress consequently applying a high tension effort combined with a significant torque lead to plastifying of the drill pipe body thus reducing its fatigue life. This problem is well observed in back-reaming operation. The results show that fatigue damage from rotation in dogleg during backreaming operation is a significant problem if the severity is greater than the critical value. So the position of drill pipe in the string will influence the amount of fatigue damage it sustains. Furthermore, back reaming can reduce the fatigue life of the drill pipe significantly because of the stress reversal of the drill string under tension in a dogle