Ultrasonic inspection of austenitic stainless steel weldments

Ultrasonic waves interact in a complex manner with the metallurgical structure of austenitic weldments resulting in ambiguity when interpreting reflections and at times in misinterpretation of defect positions. In this work, current knowledge of the structure of austenitic welds is outlined, and the influence of this structure on the propagation of ultrasonic waves is reviewed. Using an established and highly accurate technique, data on velocity variations as a function of the angle between the direction of soundwave propagation and the axes of preferred grain orientation existing in such welds, are experimentally obtained. These results and existing theory are used to provide quantitative evidence of (i) anisotropy factors in austenitic welds, (ii) beam skewing effects for different wave modes and polarizations, and (iii) the extent of acoustic impedance mismatch between parent and weld metals. The existence of "false" indications is demonstrated, and suggestions are made into their nature. The effectiveness of conventional transverse wave techniques for inspecting artificial and real defects existing in austenitic weldments is experimentally investigated, the limitations are demonstrated, and possible solutions are proposed. The possibilities offered by the use of longitudinal angle probes for ultrasonic inspection of real and artificial defects existing in austenitic weldments are experimentally investigated, and parameters such as probe angle, frequency and scanning position are evaluated. Detailed work has been carried out on the interaction of ultrasound with fatigue and corrosion-fatigue cracks in the weld metal and the heat affected zones (HAZs) of 316 and 347 types of austenitic weldments, together with the influence of elastic compressive stresses, defect topography and defect geometry. Practical applications of all results are discussed, and more effective means of ultrasonic inspection of austenitic weldments are suggested

Composition and conditions of the late Mesozoic volcanism occurrence of the northern part of the Borschovochny ridge (Eastern Transbaikalia)

On the basis of geochemical study results composition heterogeneity and formation conditions of late Mesozoic subvolcanic rocks from northern part of Borschovochny ridge by an example of shadoronsky and abgatuysky complexes are discussed. Obtained results show that volcanic rocks of both complexes have heterogeneous composition and differ from each other in level and other features of alkalinity. Rare and trace elements geochemistry study results show that there is a significant enrichment with LILE (Cs, Rb, Ba) and some depletion with HFSE (Nb, Ta), meanwhile the correlation between Th and Yb indicates conditions of active continental margin. Gd/Yb and La/Sm ratios allow to conclude that shadoronsky complex rocks originated from garnet-stable mantle source (partial melting of 5% of garnet peridotite), while abagatuysky complex rocks originated from transitional garnet-spinel mantle

Metasomatic alteration associated with the formation of subvolcanic rocks of the Abagatuysky complex (Nerchinsk ore region, Eastern Transbaikalia)

Within the northeastern edge of the Borschovochny pluton, located in Eastern Transbaikalia, a complex of small intrusions is localized, represented by the subvolcanic bodies of the Early Cretaceous Abagatuysky andesite-dacite complex. These intrusions, along with significant dynamometamorphic (tectonic) transformations, produced the development of metasomatic alteration, united in three large rock associations — propylites, beresites, and argillisites. These metasomatic associations successively replace each other as they move away from the center of heat exposure of intrusions. In addition, each of these groups of metasomatites has its own unique internal mineral zonality, and the most productive of them, on the subject of gold ore mineralization, is the beresite association

Bleeding Meckel's diverticulum diagnosis: an unusual indication for computed tomography

Despite the wide use of modern investigation techniques, the diagnosis of complications related to Meckel's diverticulum (MD) remains difficult. Arteriography is commonly indicated for acute bleeding, and radionuclide scans may help in identifying the site of intestinal hemorrhage. In contrast, computed tomography (CT) is usually considered little use in the diagnosis of bleeding MD. We present the case of a young patient with massive gastrointestinal hemorrhage, in whom the diagnosis of MD bleeding was preoperatively made with contrast-enhanced CT after two negatives arteriographie

The determinants of loan loss provisions:an analysis of the Greek banking systemin light of the sovereign debt crisis

We utilize a new set of macroeconomic and regulatory data to analyze the evolution of loan loss provisioning practices in the Greek banking system over the period 2005-2015. We explore the determinants of the aggregate loan loss reserves to total loans ratio, which reflects the accumulation of provisions net of write-offs, and constitutes an important metric of the credit quality of loan portfolios. Our results suggest that domestic credit institutions respond relatively quickly to macroeconomic shocks, though the latter’s effects on the provisioning behavior of the domestic banking system show significant persistence. Furthermore, the impact of macroeconomic shocks on the loan loss reserves ratio has become stronger (both in terms of magnitude and statistical significance) following the outbreak of the Greek sovereign debt crisis. From a macro policy perspective, this result indicates that a sustainable stabilization of macroeconomic conditions is a key precondition for safeguarding domestic financial stability. For a regulatory standpoint, it suggests that the possibility of macroeconomic regime-related effects on banks’ provisioning policies should be taken into account when macro prudential stress tests of the banking system are designed and implemented

Explaining non-performing loans in Greece: a comparative study on the effects of recession and banking practices

Using a new dataset of macroeconomic and banking-related variables we attempt to explain the evolution of “bad” loans in Greece over the period 2005-2015. Our findings suggest that the primary cause of the sharp increase in non-performing loans (NPLs) following the outbreak of the sovereign debt crisis can be mainly attributed to the unprecedented contraction of domestic economic activity and the subsequent rise in unemployment. Furthermore, our results offer no empirical evidence in support of a range of examined hypotheses assuming overly aggressive lending practices by major Greek credit institutions or any systematic efforts to boost current earnings by extending credit to lower credit quality clients. We find that the transmission of macroeconomic shocks to NPLs takes place relatively fast, with the estimated magnitude of the respective responses being broadly comparable with that documented in some earlier studies for other euro area periphery economies. Overall, our results support a swift implementation of reforms agreed with official lenders in the context of the new (3rd) bailout programme. These envisage the modernization the county’s private sector insolvency framework and the creation of a more efficient model for the management of NPLs. A vigorous implementation of these reforms is key for allowing a resumption of positive credit creation, by freeing up valuable resources that are currently trapped in unproductive sectors of the domestic economy. This, in turn, would facilitate a speedier return to positive economic growth and a gradual reduction in unemployment

Geological structure and prospects of noble metal ore mineralization of the Khayrkhan gabbroid massif (Western Mongolia)

An analysis of the distribution of noble metals in zones of sulfide mineralization makes it possible to justify the isolation of four ore-bearing horizons with a specific geochemical zonation. A rise in the gold content relative to palladium and platinum is observed from the bottom upwards along the section of the stratified series of gabbroids. The study of the mineral phases of sulphides and the noble minerals itself indicates the evolution of hydrothermal solutions, which determines the different activity and mobility of the fluid (mercury, tellurium, sulfur) and ore (copper, nickel, iron, platinum, gold and silver) components

Thermodynamic modelling of metamorphic processes: state of the art in pseudosection approach

Understanding global-scale orogenic processes related to supercontinents, and their relationship to the secular evolution of the Earth's lithosphere, represent important challenges for Earth scientists today. The record of these processes is preserved in the microstructures, mineral assemblages and mineral compositions of lithospheric rocks exhumed to the Earth's surface. Given a well-characterized microstructural evolution, thermodynamic modelling is the key to quantifying changes in pressure and temperature, with the rate of these changes being provided by rock-forming and accessory mineral-based geochronology. Thus, metamorphic rocks provide Pressure–Temperature–time–deformation (P–T–t–d) data that help to parameterize orogenic processes