Elkeme Hellenic Research Center For Metals Sa

Oinófyta, Greece

Elkeme Hellenic Research Center For Metals Sa

Oinófyta, Greece
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Vazdirvanidis A.,Elkeme Hellenic Research Center For Metals Sa | Pantazopoulos G.,Elkeme Hellenic Research Center For Metals Sa
Metallography, Microstructure, and Analysis | Year: 2017

In the present study, a comprehensive microstructural analysis of the fractured bells of Great Anthony Church of Saint Andrew Skete of Mount Athos, a significant monument of Orthodox tradition and Cultural heritage, was performed. The bronze alloy chemical composition together with metallographic examination, scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy toward the identification of the phases and other micro-constituents and discontinuities present in the internal structure was documented and illustrated in conjunction with the applied bell manufacturing process. Tin bronze alloy was used for bell making, with a chemical composition (up to 18% Sn as a main alloying element) signifying most likely that the bell was produced at the Empire era. The as-cast microstructure primarily consisted of α-dendrites and α + δ interdendritic eutectoid mixture with Pb globules and scattered porosity. Furthermore, electron backscattered diffraction analysis was conducted in order to determine texture properties and obtain crystallographic information regarding the bells’ cast structure. © 2017, Springer Science+Business Media, LLC and ASM International.


Pantazopoulos G.A.,Elkeme Hellenic Research Center For Metals Sa
Journal of Failure Analysis and Prevention | Year: 2011

Fractography is a powerful analytic tool for the evaluation of failure surface topography and root-cause analyses. Fractography, embracing both light and electron optics methods, is utilized in modern failure analysis and is recognized by the engineering community as a unique process for industrial problem solving, evaluating machinery/component failures, and providing solutions for performance improvements. In the present study, the role of fractography is highlighted through characteristic failures of industrial machinery components. Low-power stereomicroscopy and Scanning Electron Microscopy (SEM) micro-fractography are the principal analytic tools that were used in the context of the present research. © ASM International 2011.


Toulfatzis A.I.,Elkeme Hellenic Research Center For Metals Sa | Besseris G.J.,Technological Educational Institute of Piraeus | Pantazopoulos G.A.,Elkeme Hellenic Research Center For Metals Sa | Stergiou C.,Technological Educational Institute of Piraeus
International Journal of Advanced Manufacturing Technology | Year: 2011

The aim of this paper is to identify the observed differences during machining in terms of microstructure-property relationship, as well as to determine the optimum cutting conditions, using non-parametric design of experiments methods applied in turning processes of special leaded brass bars used in industrial applications. For this purpose, industrial copper alloy rods, namely CuZn39Pb3 (CW614N-Brass 583) and CuZn36Pb2As (CW602N-Brass DZR) for machining applications, were investigated as far as their microstructure and mechanical behaviour are concerned, including lead particle distribution and phase structure characterization, hardness, tensile and impact properties. Machinability was assessed qualitatively and quantitatively by evaluating the chip size and morphology and the corresponding cutting tool wear land, employing the appropriate single point turning technique. Optical and scanning electron microscopy, hardness, tensile and impact testing were used as the major analytical techniques in the context of the present investigation. Moreover, a multi-non-parametric study employing design of experiments was properly implemented in order to identify the critical-to-machinability parameters and to obtain their optimum values for high-performance production. It was found that solely the alloy Brass 583 was influential in chip morphology while the concurrent optimization with cutting tool wear only introduced excessive variation in the scheme that overall phased out any dependencies. © 2011 Springer-Verlag London Limited.


Pantazopoulos G.A.,Elkeme Hellenic Research Center For Metals Sa
Journal of Failure Analysis and Prevention | Year: 2015

The analysis of pinion gear damage operated in a tube coiler machine gearbox was investigated. Visual inspection, SEM fractographic analysis, and metallographic evaluation are employed as the principal analytical techniques for the investigation. Fractographic observations indicated the occurrence of bending fatigue started at the maximum load surface of the gear teeth, known as active flank, and propagated to the opposite area resulting in catastrophic tooth fracture. Unbalanced stress conditions led to the consecutive damage and fracture of adjacent teeth resulting in machine interruption and immediate replacement of the gear system. The multiple fatigue crack initiation sites suggest significant stress concentration probably caused likely by gear misalignment. Metallographic evaluation revealed an entirely heat-treated gear microstructure consisted of tempered martensite free from microstructural abnormality that could be associated to the failure. Regular gear inspection and system alignment checks together with the consideration of increasing surface hardness, through selected surface strengthening procedures, are suggested as further corrective actions to minimize similar failures and machine downtime in the future. © 2015, ASM International.


Pantazopoulos G.A.,Elkeme Hellenic Research Center For Metals Sa
Journal of Failure Analysis and Prevention | Year: 2010

A broken hook-shaped steel rod from a weight-lifting bridge beam was received from a plant for failure analysis. Visual, stereo, and light optical microscopy as well as hardness testing, used for fractographic, microstructural, and strength evaluation, were used as the principal analytical techniques in the investigation. Macrofractographic investigation suggests strongly that failure initiated at the weld area and was followed by torsional overload fracture of the hook body. The fracture probably originated from abnormal operation of the crane lift. © 2009 ASM International.


Pantazopoulos G.A.,Elkeme Hellenic Research Center For Metals Sa | Toulfatzis A.I.,Elkeme Hellenic Research Center For Metals Sa
Metallography, Microstructure, and Analysis | Year: 2012

Machinable brasses are a broad class of high strength copper-zinc alloys mainly containing lead to improve machinability. Conventional leaded brasses are widely used in several manufacturing sectors (i. e., fabrication of hydraulic components, fittings, valves, etc.) due to their superior workability in extrusion and drawing, together with their superior machinability for high efficiency production of final components in high speed/high precision machining centers. In addition to machinability, the mechanical behavior and general fracture mechanisms of these alloys are also important, due to their impact on the overall reliability and safety of brass components. In this study, the main fracture modes and mechanical characteristics of two industrial copper alloys, namely, CuZn39Pb3 and CuZn36Pb2As, are presented in relation to their microstructure. Optical metallography, macro- and microfractography, together with static and dynamic mechanical testing, were used as the principal analytical techniques for the present investigation. © 2012 Springer Science+Business Media, LLC and ASM International.


Pantazopoulos G.,Elkeme Hellenic Research Center For Metals Sa | Vazdirvanidis A.,Elkeme Hellenic Research Center For Metals Sa | Tsinopoulos G.,HALCOR S.A. Metal Works
Engineering Failure Analysis | Year: 2011

Unalloyed high purity copper, deoxidized with phosphorus is widely used in tubing and fittings for sanitary installations due to its ease of use and corrosion resistance properties. Certain factors related to installation operating conditions on the one hand, and improper design/installation features on the other hand, often lead to unexpected failures. The case examines a Cu-tube that failed in a pump station after 2-3 years in-service. The investigation findings suggest strongly that the failure was the result of a complex mechanism involving corrosion-erosion process, facilitated by stress-corrosion cracking mechanism. Stress-corrosion cracking referred as a delayed failure mechanism resulted from the synergistic effect of corrosive environment, susceptible material and externally applied or residual - due to the manufacturing process-stress. In case of hard-drawn tubes, the development of tensile (circumferential or hoop) stress field at the outer surface area after cold drawing, enhances the propensity for stress-corrosion cracking (SCC), especially under the presence of corrosive environment. © 2010 Elsevier Ltd.


Psyllaki P.P.,Technological Educational Institute of Piraeus | Pantazopoulos G.,Elkeme Hellenic Research Center For Metals Sa | Pistoli A.,Technological Educational Institute of Piraeus
Engineering Failure Analysis | Year: 2013

The present study concerns the failure analysis of a perforated austenitic stainless steel grid, operating in a shell-and-tube heat exchanger of a petrochemical industry. Macroscopic examination of the grid indicated extensive friability and severe cracking in a direction perpendicular to its normal loading, while both grid surfaces as well as the interior of the filtration holes were covered significantly by decayed deposits. Microscopic examination of selected grid areas, after the surface deposits removal, indicated severe cracking exhibiting multiple branching, which advocates for stress corrosion cracking. Besides the extensive cracking areas, voids surrounded by twinning and slip bands were observed. Elemental microanalysis carried out in the areas around voids indicated the presence of iron and chromium at proportions that can be correlated to the formation of σ-phase. The detection of oxygen, iron and chromium within the cracks is attributed to corrosion products consisting of a mixture of iron and chromium oxides. The premature catastrophic failure of the stainless grid occurred as a synergistic effect of these distinct root-causes. Potential substitution of the currently used stainless steel with another alloy of higher resistance in stress corrosion cracking and microstructure stability at high temperatures is suggested. © 2013 Elsevier Ltd.


Pantazopoulos G.,Elkeme Hellenic Research Center For Metals Sa | Vazdirvanidis A.,Elkeme Hellenic Research Center For Metals Sa
Case Studies in Engineering Failure Analysis | Year: 2013

Low alloy steel welded pipes buried in the ground were sent for failure analysis investigation. Failure of steel pipes was not caused by tensile ductile overload but resulted from low ductility fracture in the area of the weld, which also contains multiple intergranular secondary cracks. The failure is most probably attributed to intergranular cracking initiating from the outer surface in the weld heat affected zone and propagated through the wall thickness. Random surface cracks or folds were found around the pipe. In some cases cracks are emanating from the tip of these discontinuities. Chemical analysis, visual inspection, optical microscopy and SEM/EDS analysis were used as the principal analytical techniques for the failure investigation. © 2012 Elsevier Ltd.


Pantazopoulos G.A.,Elkeme Hellenic Research Center For Metals Sa | Toulfatzis A.I.,Elkeme Hellenic Research Center For Metals Sa
Case Studies in Engineering Failure Analysis | Year: 2013

Cracking of hexagonal brass connector of a boiler tubing assembly caused leakage and interruption of the function of a water heating circuit. Destructive damage was provoked after two years in service. Visual examination, light and scanning electron microscopy coupled with local elemental energy dispersive X-ray spectroscopy (SEM/EDS) were used as the principal analytical techniques for the present investigation. The collected investigation findings suggest that failure was induced via progressive cracking, attributed probably to fatigue initiated from surface flaws existed on the thread root surface. Recommendations mainly concerned revision of the alloy selection and quality assurance of tubing assembly procedure during installation. © 2012 Elsevier Ltd.

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