•The hydrogen effect on tensile properties was evaluated through hollow specimens.•The effect of surface roughness on hydrogen degradation magnitude was compared.•The hydrogen compatibility of ...vintage and modern X65 pipeline steels was assessed.•Hydrogen affects the tensile properties of both carbon steels in a similar way.•Lower roughness of the exposed surface correlate to lower EI and strain loss.
The transition toward a hydrogen-based economy requires a widespread transport and distribution network, and repurposed natural gas pipelines are a viable option. An assessment of the hydrogen-induced degradation of pipeline steels is needed to inject H2 gas into the existing infrastructure safely. The conservative and standardized method consists of in-situ tensile tests in an autoclave filled with high-pressure hydrogen gas. A proposed alternative method involves using a hollow specimen as containment volume and applying the gas pressure in the inner cavity. This technique has lower costs and shorter test preparation time but is not standardized yet. This study aims to evaluate and compare the tensile properties of API 5L X65 pipeline steel in two states: vintage and modern. The influence of the surface roughness is investigated through parallel tests with drilled and reamed specimens. Hydrogen tests are compared with reference tests in an inert environment. A significant hydrogen-induced decrease in tensile properties is observed, and no significant difference between vintage and modern X65 can be drawn. The reduction in tensile properties is more significant in specimens with higher inner surface roughness. The evaluation of surface conditions appears crucial when assessing the HE susceptibility of hydrogen transport and storage equipment.
The high potential of hydrogen as a key factor on the pathway towards a climate neutral economy, leads to rising demand in technical applications, where gaseous hydrogen is used. For several metals, ...hydrogen-metal interactions could cause a degradation of the material properties. This is especially valid for low carbon and high-strength structural steels, as they are commonly used in natural gas pipelines and analyzed in this work.
This work provides an insight to the impact of hydrogen on the mechanical properties of an API 5L X65 pipeline steel tested in 60 bar gaseous hydrogen atmosphere. The analyses were performed using the hollow specimen technique with slow strain rate testing (SSRT). The nature of the crack was visualized thereafter utilizing μCT imaging of the sample pressurized with gaseous hydrogen in comparison to one tested in an inert atmosphere.
The combination of the results from non-conventional mechanical testing procedures and nondestructive imaging techniques has shown unambiguously how the exposure to hydrogen under realistic service pressure influences the mechanical properties of the material and the appearance of failure.
•Visualization of hydrogen induced crack propagation using μCT.•Orientation of cracks differs in hydrogen gas compared to inert gas atmosphere.•Spread of cracks differs in hydrogen gas compared to inert gas atmosphere.
Metals that are exposed to high pressure hydrogen gas may undergo detrimental failure by embrittlement. Understanding the mechanisms and driving forces of hydrogen absorption on the surface of metals ...is crucial for avoiding hydrogen embrittlement. In this study, the effect of stress-enhanced gaseous hydrogen uptake in bulk metals is investigated in detail. For that purpose, a generalized form of Sievert's law is derived from thermodynamic potentials considering the effect of microstructural trapping sites and multiaxial stresses. This new equation is parametrized and verified using experimental data for carbon steels, which were charged under gaseous hydrogen atmosphere at pressures up to 1000 bar. The role of microstructural trapping sites on the parameter identification is critically discussed. Finally, the parametrized equation is applied to calculate the stress-enhanced hydrogen solubility of thin-walled pipelines and thick-walled pressure vessels during service.
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•Improvement of Sievert's law to consider trapping sites and stress states.•Calculation and validation of gaseous hydrogen solubility under extreme conditions.•Hydrogen uptake measured for L450 steel at 200 and 1000 bar.•Calculation of the hydrogen solubility in pipes and pressure vessels.•Comprehensive literature survey of gaseous hydrogen solubility.
Hydrogen has great potential on the path towards decarbonization of the energy and transport sectors and can mitigate the urgent issue of global warming. It can be sustainably produced through water ...electrolysis with potentially zero emissions, and efficiently used (e.g., in fuel cell systems). Despite its environmental advantages, hydrogen-metal interactions could result in the degradation of the mechanical properties of several structural materials. In order to determine the magnitude of the material degradation in relation to hydrogen exposure, extensive material testing is required. The standardized procedure for in-situ testing for the quantification of the impact of compressed gaseous hydrogen (CGH2) relies on the utilization of an autoclave around the tested specimen. Such test set-up is complex, expensive, time-consuming and requires special equipment, trained personnel, and strict safety procedures. A relatively recent method to circumvent these issues and provide affordable results consists of using hollow specimens, thus applying the hydrogen pressure inside rather than outside the specimen. It allows to reduce the volume of hydrogen by several orders of magnitude and to perform the tests more efficiently and in a safer manner. This study focuses on evaluating the tensile properties of X65 vintage pipeline steel tested in a high-pressure hydrogen environment using hollow specimens. Tests are performed in 6 MPa H2 and Ar at the nominal strain rate of 10−6 s−1 to evaluate the reduced area at fracture and the elongation loss. The effect of surface finishing on crack initiation and propagation is investigated by comparing two different manufacturing techniques. In this way, this study provides insights into the applicability of a novel, reliable, and safe testing method which can be used to assess the hydrogen-assisted ductility loss in metallic materials.
The hydrogen solubility in ferritic and martensitic steels is affected by hydrostatic stress, pressure, and temperature. In general, compressive stresses decrease but tensile stresses increase the ...hydrogen solubility. This important aspect must be considered when qualifying materials for high‐pressure hydrogen applications (e.g., for pipelines or tanks) by using autoclave systems. In this work, a pressure equivalent for compensating the effect of compressive stresses on the hydrogen solubility inside of closed autoclaves is proposed to achieve solubilities that are equivalent to those in pipelines and tanks subjected to tensile stresses. Moreover, it is shown that the temperature effect becomes critical at low temperatures (e.g., under cryogenic conditions for storing liquid hydrogen). Trapping of hydrogen in the microstructure can increase the hydrogen solubility with decreasing temperature, having a solubility minimum at about room temperature. To demonstrate this effect, the generalized law of the hydrogen solubility is parameterized for different steels using measured contents of gaseous hydrogen. The constant parameter sets are verified and critically discussed with respect to the high‐pressure hydrogen experiments.
The hydrogen solubility in ferritic and martensitic steels is affected by hydrostatic stress, pressure, and temperature. In general, compressive stresses decrease but tensile stresses increase the hydrogen solubility. This important aspect must be considered when qualifying materials for high‐pressure hydrogen applications (e.g., for pipelines or tanks) by using autoclave systems.
Diagnosis of COVID is performed by PCR methods, but their capacity is limited by the requirement of high-level facilities and instruments. The loop-mediated isothermal amplification (LAMP) method has ...been utilized for the detection of isolated virus-specific RNA. Preliminary data suggest the possibility of isothermal amplification directly from respiratory samples without RNA extraction. All patients admitted to our hospital were screened for SARS-CoV-2 by routine. Respiratory samples were tested by variplex system based on LAMP method directly without RNA extraction and by PCR. Primary endpoint was the false-negative rate of variplex test compared with PCR as gold standard. In 109 patients variplex test and PCR assay were performed simultaneously. Median age was 80 years and male/female ratio was 40/60%. The prevalence of PCR-confirmed COVID diagnosis was 43.1%. Variplex test was positive in 13.8%. False-negative rate of variplex test compared with PCR was 83.0%. The potential of LAMP technology using isolated RNA has been demonstrated impressively by others, and excellent sensitivity and specificity of detecting SARS-CoV-2 has been reported. However, without RNA extraction, the variplex test system failed to reliably detect SARS-CoV-2 directly in respiratory samples.
The basis for individual students' instructional support by teachers is an individual diagnosis of one's learning advances and difficulties. Even though sophisticated diagnostic tools exist, it ...remains an open question how diagnosis and learning can be merged into a consistent pedagogical method to support both teachers and students with feedback about the learning process. Aspects like the usage of open format questions, social inter-dependencies and heterogeneity, group-forming processes and the teachers supervision issue are taken into account. We propose a model for integration of peer assessment functionality for learning into a computer-based Adaptive Diagnostic Learning Environment to solve central problems of classroom diagnostic assessment, adaptive learning and knowledge transfer between peers in a classroom environment. The research approach focused on math learning scenarios for evaluation, but is expected to be applicable for other educational content as well. In the following paragraphs we identify several problems in classroom scenarios to be addressed, describe the model of the underlying approach, show the implementation details and explain the evaluation setup.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This book constitutes the refereed proceedings of the 7th International Conference on E-Learning and Games, Edutainment 2012, held in conjunction with the 3rd International Conference on Serious ...Games for Training, Education, Health and Sports, GameDays 2012, held in Darmstadt, Germany, in September 2012. The 21 full papers presented were carefully reviewed and selected for inclusion in this book. They are organized in topical sections named: game-based training; game-based teaching and learning; emerging learning and gaming technologies; authoring tools and mechanisms; and serious games for health.
Acquired hemophilia A (AHA) and acquired von Willebrand Syndrome (AVWS) are both rare bleeding disorders that can be associated with lymphoproliferative or autoimmune diseases. AHA is uniformly ...caused by inhibitory autoantibodies against coagulation factor VIII (FVIII), while the pathophysiology of AVWS comprises several distinct mechanisms, including reduced synthesis, accelerated clearance, or increased proteolysis. In this regard, autoantibodies to von Willebrand factor (VWF) have been described in patients with systemic lupus erythematosus (SLE) or monoclonal gammopathy. Here, we report the case of a 71-year-old patient with a recent onset of spontaneous mucocutaneous and soft-tissue bleeding due to severely decreased FVIII and VWF. While there was no evidence for monoclonal gammopathy, specific IgG antibodies against both FVIII and VWF were detected. Furthermore, VWF multimer analysis revealed the presence of ultralarge plasma multimers and absence of the typical multimeric triplet structure, a finding consistent with decreased proteolytic processing of massively released, but rapidly cleared VWF. Both FVIII and VWF readily responded to immunosuppressive therapy with prednisolone. Interestingly, clinical and laboratory findings established the diagnosis of "late-onset SLE" in our patient. Thus, about 45 years after the first description of AVWS in a 12-year-old boy with SLE, we present another unusual case of concomitant autoimmune-mediated AHA and AVWS in an elderly SLE patient, which, to the best of our knowledge, has not been reported so far.
Zusammenfassung
Serious Games sind hochkomplex. Sie verbinden Game-Technologien und spielerische Konzepte mit weiteren Technologien und relevanten Konzepten für die verschiedenen Einsatzgebiete von ...Serious Games. Im Beitrag werden wissenschaftlich-technische Methoden, Konzepte und Software-Lösungen zur Erstellung, Steuerung und Evaluation von Serious Games vorgestellt, die in der Gruppe Serious Games am Fachgebiet Multimedia Kommunikation der TU Darmstadt entwickelt wurden. Praxisbeispiele umfassen die Bereiche Bildung und Training sowie Sport und Gesundheit.
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