Applications in metallurgy of X-ray computed tomography with variable focal spot-size and infrared thermography [Impieghi della tomografa computerizzata rX a fuoco variabile e della termografa attiva ad infrarossi in settori di interesse metallurgico]
Bonaccorsi L.,Messina University |
Garesci F.,Messina University |
Giacobbe F.,INAIL Settore Ricerca |
Freni F.,Messina University |
And 3 more authors.
Metallurgia Italiana | Year: 2013
Industrial X-ray tomography and active infrared thermography are very promising imaging techniques. Computed tomography (CT) is performed scanning samples through a X-ray beam (fig. 1); after the acquisition of the transmitted radiation (fig. 2), a suitable mathematical algorithm returns the scanned volume in digital form (fig. 3). Currently there is a wide range of CT equipments for industrial applications, ranging from linear accelerators , that cross steel walls with thicknesses up to 300 mm, to optical systems for the study of microelectronic components . CT is used in the field of non destructive testing , to study porous materials such as metal foams  and in applications of reverse engineering . Active infrared thermography, recognized as a valuable tool to identify cracks and other types , is based on the thermal transient generated by an external source : defects and discontinuities modify the thermal flux induced inside the material, causing anomalies in the surface distribution of temperatures that are measured by an infrared camera . In previous works CT  and active infrared thermography  applications have been experimented. This paper reports results of the two techniques in areas of interest for metallurgy. The working geometry of a tomographic system is showed in fig. 4. The three-dimensional return of the object is obtained through algorithms  developed from the early studies of J. Radon . The observable object size decreases strongly with the increasing of the resolving power, as outlined in figure 5. The tomographic system utilized (figures 6 and 7) works at an acceleration voltage up to a maximum of 225 kV, in the range microfocus-macrofocus, changing the spot size from 250 to 800 m, in order to give priority to spatial resolution (between 30 and 200 um), penetration capacity in materials with high absorption (up to 10 mm in the case of ferrous alloys) or object under examination size (diameter 180 mm, height 250 mm). Active infrared thermography performs radiometric measurements of the temperature distribution generated by halogen lamps, flash or jets of heated air (optical methods) , or ultrasounds (acoustic methods) . In the ultrasonic technique experimented in this work (fig. 8), a piezo-ceramic transducer, coupled to the surface of the object under examination, generates acoustic waves (vibrations) at high frequency, that are locally converted into heat by dissipative phenomena at internal discontinuities. The excitation signal consists of an ultrasonic wave (carrier signal, with a frequency ranging between 15 and 25 kHz), modulated in amplitude by a low frequency signal (signal of lock-in, with a frequency between 0.01 and 2 Hz). The correct time synchronization between the excitation and the acquire signal is an essential aspect of the lock-in technology. The emitted radiation acquisition is performed by means of an infrared camera with high spatial resolution (640 ∼ 512 pixels), equipped with a focal plane array of indium antimonide. The detector operates in the spectral range MWIR (3 to 5 mm) and has a temperature resolution of about 20 mK at room temperature. The data acquisition system works at an integration time in the range between 10 ms and 5 ms, with a frame frequency up to 100 Hz at full resolution. The images in figure 9 give an application example of CT: they show a joint, butt welded by laser beam, between two carbon steel plates clad by hot rolling with a Ni alloy. The defects, at the resolving power limit of the system and not detectable with thermographic technique, have the typical aspect of porosity. Due to their cellular nature, thermographic technique is not applicable to the study of metal foams, while CT is particularly useful to evaluate shape and size of cells. Figure 10 shows the three-dimensional reconstruction of an aluminum alloy foam with closed cells and the image of a section. The study of cells evolution during compression can be performed by tomography without having to cut samples. Figure 11 shows some sections of a steel tube filled with an aluminum alloy foam: adhesion problems between wall and foam filler are highlighted. Thermography and tomography offer the possibility to perform dimensional investigation of industrial products and defects monitoring. Specifically, it was considered a cast iron collector for an automotive turbine produced by casting. Figure 12 shows a phase image of this component obtained by the ultrasonic active thermography: the presence of a darker area is indicative of an internal defect. To assess shape and size of the defect, tomographic sections at parallel planes spaced apart by 0.2 mm are considered (fig. 13). In Figure 14, close to the photographic image of a cast iron sample for tensile test, thermographic and tomographic surveys are reported for comparison. The two techniques show defects of small sizes. In particular, CT allows to analyze defects by means of longitudinal and transverse sections and identify both spatial position and morphology (figs. 14 and 15).
Alvino A.,INAIL Settore Ricerca |
Antonini A.,INAIL Settore Ricerca |
Lega D.,INAIL Settore Ricerca
Engineering Failure Analysis | Year: 2014
After 10years of service, one high-pressure cylinder made by 34CrMo4 low alloy steel fractured catastrophically, causing extensive damages. The cylinder was filled with a commercially available mixture of nitrogen, argon and carbon dioxide. A failure analysis has been carried out in order to identify the cause of rupture. The examination of cross sections specimens has revealed several branched cracks originating at cylinder inner wall side and propagating across the bulk. The observation of fracture surfaces supported the hypothesis of an environmental attack that affected the cylinder inner surface. No evidences of other damage form have been found: the chemical analysis, the microstructure examination and the mechanical tests performed provided results in full compliance with the technical specifications of the alloy. On the basis of such considerations, it can be assumed that the cylinder fractured by stress corrosion cracking. The exposition to a CO/CO2 containing atmosphere in presence of undesired traces of moisture promoted the local damage, as long as the applied tensile stress triggered cracks formation and propagation. Then, a progressive reduction of the effective toughness occurred, leading to a sudden, catastrophic, overload rupture. © 2014 Elsevier Ltd.
Veschetti E.,Istituto Superiore di Sanita |
Notardonato I.,University of Molise |
Avino P.,INAIL Settore Ricerca |
Russo M.V.,University of Molise
Journal of Separation Science | Year: 2013
GC column selectivity can be continuously adapted to suit analytical needs using a flow-tuneable tandem system. Its application for the separation of complex mixtures requires a deep understanding of the theory in this area. Although a number of researchers have developed specific models, a general and exhaustive theory is still missing. In this paper, we have made an implementation of pre-existing models on tandem-column assemblies operated isothermally. In particular, we have investigated the effect of column length and diameter, phase thickness, and oven temperature on chromatographic parameters, such as capacity factor, selectivity, and intrinsic resolution. A new approach for the correct choice of the working temperature has been proposed. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Caporossi L.,INAIL Settore Ricerca |
Papaleo B.,INAIL Settore Ricerca |
Capanna S.,INAIL Settore Ricerca |
Calicchia S.,INAIL Settore Ricerca |
And 3 more authors.
Giornale Italiano di Medicina del Lavoro ed Ergonomia | Year: 2015
The aim of this study was to compare the different approaches used for chemical risk assessment, in relation to the perception of risk for operators, in some research laboratories of a hospital in Rome. All information regarding the chemicals used for the application of three algorithmic models for chemical risk assessment ("Movarisch", "Inforisk", "Archimede") were collected. An environmental and biological monitoring and a study on the combined exposure to multiple chemicals using the World Health Organization proposed steps were carried out. A questionnaire was prepared for the identification of risk perception. An estimation of chemical risk with algorithms was compared with data from monitoring: findings showed that estimated risk was higher than those identified with airborne or urine concentrations, always under their limit values. The study of multiple exposure showed a possible cumulative risk, in some cases, but the conditions of use (volume and time) often bring to a reduced one. The perception of risk attributed to the monitored hazardous substances showed a correct perception in all laboratories and for all workers, with regard to the substances manipulated.
Persechino B.,INAIL Settore Ricerca |
Fontana L.,INAIL Settore Ricerca |
Laurano P.,INAIL Settore Ricerca |
Buresti G.,INAIL Settore Ricerca |
And 8 more authors.
Giornale Italiano di Medicina del Lavoro ed Ergonomia | Year: 2014
The technological advancements, the occurrence of new emerging occupational risks and diseases, and the changes in the regulatory framework for occupational health and safety induce a constant evolution of occupational medicine. Consequently, the skills and training needs of the occupational physicians should be periodically revalued and upgraded in order to identify technical and operational issues and problems of this discipline. In this context, the aim of this national survey, carried out using a self-administered questionnaire submitted to a sample of 1,237 occupational physicians, has been to gain helpful information to ensure a continuous improvement of the quality and effectiveness of measures aimed at protecting the health and safety of workers. The questionnaire, that consists of 43 questions divided into 5 different areas (personal and professional information, training and updating needs of occupational physicians, professional activities and relationships with the corporate prevention system, relationships with the supervisory board of the Local Health Authority, relationships with the National Health Service), allowed to obtain personal and professional data, to assess the training needs and demands of occupational physicians and to evaluate their relationships with the other stakeholders of the Italian prevention system and with the National Health Service. The preliminary results of this survey appear extremely important. In fact, this findings, highlighting the current problems of occupational physician, constitute the starting point to identify, develop and implement management methodologies, operative procedures and training programs that are effective and modern.