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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. Source

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. Source

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. Source

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. Source

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. Source

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