Evaluación de la integridad estructural de tubos de generadores de vapor con defectos volumétricos debidos al fretting.

Los Generadores de vapor (GVs) en una central nuclear están conformados por un manojo de tubos que actúan como una barrera entre el sistema primario contaminado y el secundario. A través de los tubos de GVs (TGVs) se desarrolla el intercambio de calor que produce el vapor que después accionará las turbinas de la central. Estos componentes están sometidos a unas condiciones térmicas, químicas y mecánicas bastante severas, que pueden provocar la aparición de defectos geométricos y volumétricos comprometiendo su integridad estructural. Es por esta razón que el mantenimiento de los GVs es importante para la operación económica y segura de las centrales nucleares. Uno de los principales mecanismos de desgaste de los tubos de GVs es el fenómeno conocido como fretting. El mismo provoca el adelgazamiento de las paredes de los TGVs debido a pequeños movimientos relativos entre superficies en contacto. Dado el caso particular de los GVs del reactor CAREM-25 en los que el circuito primario se encuentra del lado externo de los tubos que lo constituyen, la ocurrencia de este mecanismo de daño podría comprometer la integridad de los mismos haciéndolos más susceptibles al daño por colapso. El presente trabajo constituye una continuación del Proyecto integrador finalizado en el 2015 por Pablo Lazo en el que se evaluó la influencia de efectos de ovalización en el colapso de los tubos de los GVs. Se evalúa ahora la influencia de defectos volumétricos debido a fretting. Esto se realizó a través de modelos numéricos que estiman la presión de colapso en los tubos con y sin defecto. Los resultados de los modelos se compararon con resultados de expresiones analíticas obtenidas por otros autores, valores experimentales propios y otros valores de referencia. A partir del análisis de los resultados se derivaron algunas conclusiones que ayudan a entender el comportamiento de los tubos de GVs con defectos debido a mecanismo de daño por fretting. Además se desarrollaron expresiones matemáticas que ayudan a definir las dimensiones de los defectos que comprometen la integridad estructural de los TGVs en el caso del reactor CAREM-25.

Evaluación de la integridad estructural de tubos de generadores de vapor con defectos volumétricos debidos al fretting.

Los Generadores de vapor (GVs) en una central nuclear están conformados por un manojo de tubos que actúan como una barrera entre el sistema primario contaminado y el secundario. A través de los tubos de GVs (TGVs) se desarrolla el intercambio de calor que produce el vapor que después accionará las turbinas de la central. Estos componentes están sometidos a unas condiciones térmicas, químicas y mecánicas bastante severas, que pueden provocar la aparición de defectos geométricos y volumétricos comprometiendo su integridad estructural. Es por esta razón que el mantenimiento de los GVs es importante para la operación económica y segura de las centrales nucleares. Uno de los principales mecanismos de desgaste de los tubos de GVs es el fenómeno conocido como fretting. El mismo provoca el adelgazamiento de las paredes de los TGVs debido a pequeños movimientos relativos entre superficies en contacto. Dado el caso particular de los GVs del reactor CAREM-25 en los que el circuito primario se encuentra del lado externo de los tubos que lo constituyen, la ocurrencia de este mecanismo de daño podría comprometer la integridad de los mismos haciéndolos más susceptibles al daño por colapso. El presente trabajo constituye una continuación del Proyecto integrador finalizado en el 2015 por Pablo Lazo en el que se evaluó la influencia de efectos de ovalización en el colapso de los tubos de los GVs. Se evalúa ahora la influencia de defectos volumétricos debido a fretting. Esto se realizó a través de modelos numéricos que estiman la presión de colapso en los tubos con y sin defecto. Los resultados de los modelos se compararon con resultados de expresiones analíticas obtenidas por otros autores, valores experimentales propios y otros valores de referencia. A partir del análisis de los resultados se derivaron algunas conclusiones que ayudan a entender el comportamiento de los tubos de GVs con defectos debido a mecanismo de daño por fretting. Además se desarrollaron expresiones matemáticas que ayudan a definir las dimensiones de los defectos que comprometen la integridad estructural de los TGVs en el caso del reactor CAREM-25.

Relargage d’ions métalliques après l’arthroplastie de la hanche à grand diamètre avec couple de frottement métal sur métal

La dégénérescence articulaire sévère de la hanche est une pathologie fréquente et son traitement ultime est le remplacement prothétique. L’arthroplastie la plus répandue au monde est la prothèse totale de hanche (PTH) avec un couple de frottement métal-sur-polyéthylène (MPE). Cependant ce type d’intervention présente une longévité limitée à cause de l’usure de PE et ne convient pas aux patients actifs souffrant de coxarthrose sévère tôt dans leur vie. Afin de palier à ce problème, une nouvelle génération de surfaces de frottement métal-sur-métal (MM) est actuellement employée. Ces surfaces de frottement sont utilisées en PTH avec tête de 28 mm, en resurfaçage (RH) et avec la PTH à tête de grand diamètre. Alors qu’il y a beaucoup d’évidence à l’égard du bon fonctionnement des implants PTH 28 mm et du RH, les données quant aux performances in vivo des PTH MM à grand diamètre manquent. Malgré cela, ces implants sont utilisés à grande échelle. Dans un premier temps, l’objectif de ce travail de recherche était d’évaluer l’effet et de comparer les taux d’ions chrome (Cr) et cobalt (Co) chez des sujets porteurs de PTH MM à grand diamètre à ceux de 64 porteurs de RH, tous deux possédant des surfaces de frottement aux propriétés tribologiques identiques. Dans un deuxième temps, nous avons comparé les taux ioniques (Cr, Co et titane (Ti)) entre quatre PTH MM à grand diamètre provenant de fabricants différents (Zimmer, DePuy, Smith & Nephew et Biomet). Les mesures d’ions étaient effectuées dans le sang entier dans un laboratoire indépendant par la technique de spectrophotométrie de masse à haute résolution HR-ICP-MS, pour l’ensemble de ce travail de recherche. Les deux comparaisons ont démontré le rôle crucial joué par la modularité au niveau de la jonction tête-col des PTH MM à grand diamètre. En effet, des écarts considérables dans les concentrations ioniques de Co ont été retrouvés entre les RH et PTH Durom ayant un couple de frottement identique, ainsi qu’entre les 4 différents designs de PTH MM à grand diamètre comparés entre eux. La PTH MM à grand diamètre Durom était la moins favorable alors que celle de Biomet était la plus performante. Nos observations démontrent que des sources inattendues comme la jonction tête-col de certains implants PTH MM à grand diamètre peuvent contribuer au relargage ionique systémique. Une meilleure compréhension de ce phénomène est indispensable avant l’utilisation clinque de nouveaux implants de ce type.

Analysis of retrieved shoulder prostheses

In the last years the number of shoulder arthroplasties has been increasing. Simultaneously the study of their shape, size and strength and the reasons that bring to a possible early explantation have not yet been examined in detail. The research carried out directly on explants is practically nonexistent, this means a poor understanding of the mechanisms leading the patient and so the surgeon, to their removal. The analysis of the mechanisms which are the cause of instability, dislocation, broken, fracture, etc, may lead to a change in the structure or design of the shoulder prostheses and lengthen the life of the implant in situ. The idea was to analyze 22 explants through three methods in order to find roughness, corrosion and surface wear. In the first method, the humeral heads and/or the glenospheres were examined with the interferometer, a machine that through electromagnetic waves gives information about the roughness of the surfaces under examination. The output of the device was a total profile containing both roughness and information on the waves (representing the spatial waves most characteristic on the surface). The most important value is called "roughness average" and brings the average value of the peaks found in the local defects of the surfaces. It was found that 42% of the prostheses had considerable peak values in the area where the damage was caused by the implant and not only by external events, such as possibly the surgeon's hand. One of the problems of interest in the use of metallic biomaterials is their resistance to corrosion. The clinical significance of the degradation of metal implants has been the purpose of the second method; the interaction between human body and metal components is critical to understand how and why they arrive to corrosion. The percentage of damage in the joints of the prosthetic components has been calculated via high resolution photos and the software ImageJ. The 40% and 50% of the area appeared to have scratches or multiple lines due to mechanical artifacts. The third method of analysis has been made through the use of electron microscopy to quantify the wear surface in polyethylene components. Different joint movements correspond to different mechanisms of damage, which were imprinted in the parts of polyethylene examined. The most affected area was located mainly in the side edges. The results could help the manufacturers to modify the design of the prostheses and thus reduce the number of explants. It could also help surgeons in choosing the model of the prosthesis to be implanted in the patient.

In-Vivo Corrosion and Fretting of Modular TI-6AL-4V/CO-CR-MO Hip Prostheses: The Influence of Microstructure and Design Parameters

The purpose of this study was to evaluate the incidence of corrosion and fretting in 48 retrieved titanium-6aluminum-4vanadium and/or cobalt-chromium-molybdenum modular total hip prosthesis with respect to alloy material microstructure and design parameters. The results revealed vastly different performance results for the wide array of microstructures examined. Severe corrosion/fretting was seen in 100% of as-cast, 24% of low carbon wrought, 9% of high carbon wrought and 5% of solution heat treated cobalt-chrome. Severe corrosion/fretting was observed in 60% of Ti-6Al-4V components. Design features which allow for fluid entry and stagnation, amplification of contact pressure and/or increased micromotion were also shown to play a role. 75% of prosthesis with high femoral head-trunnion offset exhibited poor performance compared to 15% with a low offset. Large femoral heads (>32mm) did not exhibit poor corrosion or fretting. Implantation time was not sufficient to cause poor performance; 54% of prosthesis with greater than 10 years in-vivo demonstrated none or mild corrosion/fretting.

Effect of equal channel angular extrusion on wear and corrosion behavior of the orthopedic Ti-13Nb-13Zr alloy in simulated body fluid

We report investigations on the texture, corrosion and wear behavior of ultra-fine grained (UFG) Ti-13Nb-Zr alloy, processed by equal channel angular extrusion (ECAE) technique, for biomedical applications. The microstructure obtained was characterized by X-ray line profile analysis, scanning electron microscope (SEM) and electron back scattered diffraction (EBSD). We focus on the corrosion resistance and the fretting behavior, the main considerations for such biomaterials, in simulated body fluid. To this end. potentiodynamic polarization tests were carried out to evaluate the corrosion behavior of the UFG alloy in Hanks solution at 37 degrees C. The fretting wear behavior was carried out against bearing steel in the same conditions. The roughness of the samples was also measured to examine the effect of topography on the wear behavior of the samples. Our results showed that the ECAE process increases noticeably the performance of the alloy as orthopedic implant. Although no significant difference was observed in the fretting wear behavior, the corrosion resistance of the UFG alloy was found to be higher than the non-treated material. (c) 2012 Elsevier B.V. All rights reserved.

Raman spectroscopy of the copper chloride minerals nantokite, eriochalcite and claringbullite - implications for copper corrosion

The application of Raman spectroscopy to the study of the copper chloride minerals nantokite, eriochalcite and claringbullite has enabled the vibrational modes for the CuCl, CuOH and CuOH2 to be determined. Nantokite is characterised by bands at 205 and 155 cm-1 attributed to the transverse and longitudinal optic vibrations. Nantokite also has an intense band at 463 cm-1, eriochalcite at 405 and 390 cm-1 and claringbullite at 511 cm-1. These bands are attributed to CuO stretching modes. Water librational bands at around 672 cm-1 for eriochalcite have been identified and hydroxyl deformation modes of claringbullite at 970, 906 and 815 cm-1 are observed. Spectra of the three minerals are so characteristically different that the minerals are readily identified by Raman spectroscopy. The minerals are often determined in copper corrosion products by X-ray diffraction. Raman spectroscopy offers a rapid, in-situ technique for the identification of these corrosion products.

Corrosion studies on the plasma-sprayed nanostructured titanium dioxide coating

Purpose: The purpose of this paper is to report the resistance of plasma-sprayed titanium dioxide (TiO2) nanostructured coatings in a corrosive environment.----- Design/methodology/approach: Weight loss studies are performed according to ASTM G31 specifications in 3.5?wt% NaCl. Electrochemical polarization resistance measurements are made according to ASTM G59-91 specifications. Corrosion resistance in a humid and corrosive environment is determined by exposing the samples in a salt spray chamber for 100?h. Microstructural studies are carried out using an atomic force microscope and scanning electron microscope.----- Findings: The nanostructured TiO2 coatings offer good resistance to corrosion, as shown by the results of immersion, electrochemical and salt spray studies. The corrosion resistance of the coating is dictated primarily by the geometry of splat lamellae, density of unmelted nanoparticles, magnitude of porosity and surface homogeneity.----- Practical implications: The TiO2 nanostructured coatings show promising potential for use as abrasion, wear-resistant and thermal barrier coatings for service in harsh environments.----- Originality/value: The paper relates the corrosion resistance of nanostructured TiO2 coatings to their structure and surface morphology.

Novel corrosion sensor based on carbon nanotube composites for structural health monitoring

Bridges are important infrastructures of all nations and are required for transportation of goods as well as human. A catastrophic failure can result in loss of lives and enormous financial hardship to the nation. Hence, there is an urgent need to monitor our infrastructures to prolong their life span, at the same time catering for heavier and faster moving traffics. Although various kinds of sensors are now available to monitor the health of the structures due to corrosion, they do not provide permanent and long term measurements. This paper investigates the fabrication of Carbon Nanotube (CNT) based composite sensors for structural health monitoring. The CNTs, a key material in nanotechnology has aroused great interest in the research community due to their remarkable mechanical, electrochemical, piezoresistive and other physical properties. Multi-wall CNT (MWCNT)/Nafion composite sensors were fabricated to evaluate their electrical properties when subjected to chemical solutions, to simulate a chemical reaction due to corrosion and real life corrosion experimental tests. The electrical resistance of the sensor electrode was dramatically changed due to corrosion. The novel sensor is expected to effectively detect corrosion in structures based on the measurement of electrical impedances of the CNT composite.

Insights into the nature of the coupling interactions between uracil corrosion inhibitors and copper : a DFT and molecular dynamics study

In this study, the nature of the coupling interactions between copper and uracil as well as its several derivatives has been systematically investigated employing the atoms in molecules (AIM) theory and energy decomposition analyses. The whole interaction process has been investigated through the analyses of the radial distribution functions of the Cu⋯X (X = S and O) contact on the basis of the ab initio molecular dynamics. No direct relationship between the adsorption strengths and inhibition efficiencies of the inhibitors has been observed. Additionally, the possibility of the methyl-substituted dithiouracil species to act as copper corrosion inhibitors has been tested.

A facile chemical screening method for the detection of stress corrosion cracking in 9 carat gold alloys

Stress corrosion cracking (SCC) is a well known form of environmental attack in low carat gold jewellery. It is desirable to have a quick, easy and cost effective way to detect SCC in alloys and prevent them from being used and later failing in their application. A facile chemical method to investigate SCC of 9 carat gold alloys is demonstrated. It involves a simple application of tensile stress to a wire sample in a corrosive environment such as 1–10 % FeCl3 which induces failure in less than 5 minutes. In this study three quaternary (Au, Ag, Cu and Zn) 9 carat gold alloy compositions were investigated for their resistance to SCC and the relationship between time to failure and processing conditions is studied. It is envisaged that the use of such a rapid and facile screening procedure at the production stage may readily identify alloy treatments that produce jewellery that will be susceptible to SCC in its lifetime.