Liste des documents
INFLUENCES DUES AUX LIGNES AERIENNES DE TRANSPORTD'ENERGIE SUR LES PIPELINES ENTERRESPROBLÈMES ET SOLUTIONS
L'interférence électromagnétique causée par des lignes de transport d'énergie électrique haute tension aux canalisations enterrées de pétrole et de gaz est à l'étude pendant beaucoup d’années. Particulièrement pendant les conditions de panne, et même en fonctionnement normal, des courants et des tensions sont induits sur les canalisations qui peuvent accélérer la corrosion du métal de la canalisation. Les résultats présentés dans ce document illustrent bien la tension induite due au champ magnétique sur les pipelines produits par les lignes électriques de haute tension en fonctionnement normal. Cet effet résulte un processus de corrosion auxquels nous avons proposé certaines solutions. Voir les détails
Mots clés : Ligne électrique HT, champ magnétique, pipelines, tension induite, corrosion, Protection cathodique
Influence of freezing rate and temperature on the hydruration of zircaloy-4.
The diffusion of hydrogen in zircaloy-4 ‘Zry-4’ generates the formation of hydrides, which may lead to dangerous embrittlement of the material. Thus, the uncontrolled nucleation and growth of these phases (hydrides) can bring the formation of severe cracks of considerable sizes which may lead to catastrophic ruptures The aim of this work is to study the nature of the microstructure obtained during an artificial loading by hydrogen of Zry-4 plates. The main variables of study of the material’s behavior in a hydrogenated environment are; the temperature, dwelling time and the cooling rate. The results obtained are very encouraging because they allowed us to identify the conditions of treatments, which would prevent the formation and propagation of cracks, preventing thus catastrophic ruptures and ultimately nuclear accidents Voir les détails
Mots clés : Zircaloy-4, Hydrides, Artificial loading, Hydrogen, Cooling rate
Effects of weld parameters on the grain refinement in AISI 430 FSS welds
Ferritic stainless steels (FSS), in general, and the first generation of the group 430, in particular, are associatedwith many problems during the welding process. These problems are the grain growth, both in the fusion zone (FZ)and heat affected zone (HAZ) and martensite formation at grain boundaries of the weld.The grain growth of ferrite at high temperature and the presence of martensite are that resilience at ambienttemperature is generally low, so that the assembly becomes susceptible to fragile fracture. The grain size can bereduced by accelerating the thermal cycle, or by reducing the energy input during the welding process.The aim of the work is, first to characterize the microstructure of welds steel (AISI 430) as variable parameters andthen optimize its own parameters. We focused on improving refining the grain size of ferritic stainless steel (AISI430) during the TIG welding (Tungsten Inert Gas).The results obtained in the present study show that, the microstructural characteristics of the weld are influencedby the current and the welding speed and beyond a critical value of current, speed has no influence. Voir les détails
Mots clés : Welding parameters, TIG, ferritic stainless steel, Grain Size
Structure and stability of Fe2(Zr1-xNbx) Laves Phases
The Laves phase structures (C15, C14 and C36) exist in a large number of binary andternary intermetallic compounds of composition AB2. Although they are well known sincelong time ago, there are still unsolved problems concerning the stability of the respectivecrystal structures. Therefore, it is difficult to predict which of the three structure types is thestable one for a given laves phase compound. In this sense, several calculation methods havebeen successfully applied to predict the stable ground state structure of various laves phases,but these calculations are restricted to the stoichiometric compositions and at 0 K. However inreal systems the stability of laves phase type is a function of temperature and composition andalso different Laves phases types may coexist in a single system. This is the subject of thepresent work, where we applied the quasi harmonic approximation implemented on Gibbs2program and the Ab initio pseudopotential method to study the temperature and composition-dependence transformations in the Laves phase Fe2(Zr1-x,Nbx) system. The results show acomplex behavior with a cyclic variation of the stable structure types as function oftemperature and Niobium concentration. Voir les détails
Mots clés : Laves Phases, First-Principles calculations, Stability, Heat of Formation, Thermal Properties and Gibbs2 Program
Precipitation phenomenon study in austenoferritic steel of 22% chromium and 5% nickel during aging treatment.
The aim of this study is to refine the duplex microstructure without using the conventional processes, as the thermo mechanical treatments. The adopted way consists in carrying out and optimizing aging and annealing heat treatments. A preliminary treatment of hardening since 1250°C was applied to increase the proportion of ferrite in the matrix. The treatments of aging were carried out at the temperature of 850°C during variable duration periods from 02h, 10h and 30 hours. The refinement of the grains had mainly on the level of ferrite, this being with the simultaneous germination of ferrite and austenite during the dissolution of the precipitates.. Voir les détails
Mots clés : duplex stainless steel, heat treatment, microstructure, grain refinement
Characterization of a welded joint in steel API.5L.X70 having undergone successive repairs
The object of this paper is to study the effect of the successive repairs on the weldment quality, knowing that these repairs constitute a main problem in the hydrocarbons transportation industry. We study the effect of several thermal cycles welding on the microstructural welding joints evolution, particularly the heat affected zones and its extend. We weld and repair many times a steel sample used in the hydrocarbons transportation. The metallographic analysis and mechanical tests results show the harmful effect of repairs that cause a prejudice on the life of weldment Voir les détails
Mots clés : welding, Repair, Thermal cycle, Heat affected zone
Passive control of tubes by crosscorrelation of ambient noise fields
The tube or pipeline are used for the routing of the uids such asgas, oil or water. The tubes deteriorate during its life. This dete-rioration can reveal defects, from where need for controlling of suchstructure. It is interesting to be able to detect damages in tubes byusing a passive control method. The goal of this work is to show inexperiments the possibility of using the function of cross correlation,between tow signals of noise, in order to make a passive control of thetubular structures. The noise in the tube was generated by ow of uid.The reproducibility of the function of cross correlation and its sensi-tivity to the presence of a defect, were checked for several frequenciesin the frequently band of [200 Hz, 35kHz]. Moreover, the movementof the uid in the tube generates a temperature variation; the inu-ence of this temperature variation on the cross correlation function wasstudied. Voir les détails
Mots clés : Green function, ambiant noise, cross corrélation, tube, flow fluide
THE EFFECT OF SUCCESSIVE REPAIRS ON THE WELDMENT QUALITY OF API 5L X 52 STEEL PIPES
This work presents the study of the influence of successive repairs on the microstructure and mechanical behavior of the HAZ in a welded HSLA steel API X52. The results show that the succession of repairs in the same area has a direct influence on the microstructure morphology for all the welded joints samples when the mechanical properties by means of tension tests agree well with standards. However, the obtained values of the tensile strength of the various welded pipes are acceptable by the standards which imply the qualification of the welding process for all the repairs. Therefore, the previous investigations lead to the conservation of the same mechanical properties, i.e. the possibility of making more repairs that the standards specify. The grain size of the HAZ obtained after the first repair decrease in impact strength value as the number of repairs increases. Voir les détails
Mots clés : welding, Repair, Heat affected zone
Damage evaluation in composite laminate by the use of ultrasonic lamb wave
This paper presents some ultrasonic methods to detect and to characterize defects, possibly obtained after damage caused in composite materials. Firstly, artificial defects are located by two piezoelectric transducers. A two-dimensional ultrasonic cartography C-scan, performed section by section, at different positions which took part through the thickness of a carbon fiber-reinforced plastic composite beam, to be analyzed. Next, fundamental symmetric S0 mode of Lamb waves is used to measure the size of the delamination by scanning over the surface beneath which a delamination lies. A remarkable decrease in the arrival time due to the delamination is detected, and the delamination length can be calculated based on a simple model for Lamb-wave propagation. Furthermore, the delamination edge is located as a sudden decrease in the amplitude. The rate of decrease in amplitude of an individual pulse cycle was detected to vary with the depth of the delamination, being most sensitive to delaminations near the surface of the plate. This is particularly useful when sizing for defects close to the surface, where a normal-incidence pulse-echo ultrasonic method has problems, particularly when the depth of the defect or the back-wall echoes lie within the length of the transmitted ultrasonic pulse. The technique has potential for faster c-scanning of a complete plate than the usual normal-incidence pulse-echo method. Voir les détails
Mots clés : composite, Ultrasonic C-scan, laminate plate, delamination, Lamb waves
ETUDE THERMIQUE DE COMPORTEMENT DU BAIN DE FUSION LORS DU SOUDAGE TIG – ÉVOLUTION 2D TRANSVERSALE-
Dans ce travail nous nous intéressons à la modélisation et la simulation thermique du comportement du bain de fusion lors le soudage TIG (Tungstène Inert Gaz). Dans un premier temps, nous décrivons un modèle mathématique du transfert du flux thermique créé par l'arc électrique du procédé sans métal d’apport. Ce modèle tient compte l’effet du changement de phases et néglige les effets convectifs dû au mouvement du fluide dans une première approche. Dans un second temps, une simulation numérique (2D axisymétrique) par la méthode des éléments finis du soudage TIG d’une tôle en acier inoxydable 304L est menée. Donc, nous avons implanté notre modèle dans le code du calcul Comsol®4.2. Les résultats obtenus concernent les champs thermiques à de différents instants décrivant la progression en profondeur et l’évolution de la fonction d’interface liquide/solide (fraction liquide). Selon la littérature nos résultats montrent une bonne concordance Voir les détails
Mots clés : modélisation thermique, soudage TIG, Comsol®, acier inoxydable