查看更多>>摘要：? 2022 Elsevier LtdHydrogen provides a workable scheme for lightening heavy oil, but it also brings ammonium chloride (NH4Cl) corrosion which could further lead to heat exchanger tubes leakage failure during hydrocracking. Moreover, the hydrogen entering steel may shorten the service life of the material. Therefore, the effect of hydrogen on failure of the heat exchanger tube material exposed to 3.5 wt% NH4Cl solution analyzed and verified experimentally. The pitting susceptibility, semiconductive properties, surface morphologies, components of passive film were investigated using electrochemical techniques, surface characterization and Mott-Schottky analysis. The results show that hydrogen substantially decreases the charge transfer resistance and the pitting potential, and simultaneously increases the OH–/O2– ratio and the densities of point defects in passive film. The results indicate that hydrogen increases the pitting corrosion susceptibility of specimens and weaken the pitting corrosion resistance of heat exchanger tube material during hydrocracking, thus the failure occurs.
查看更多>>摘要：? 2022 The AuthorsThe main objective of the ongoing research is data collection for integrity management tasks, helping the transporting pipeline operators in different decision situations. On the one hand, can be used the composite repairing and reinforcing systems for a long-term; or there are only appropriate for a short-term maintenance period. On the other hand, can be identified the reserves of the girth welds after a long-term operation; or the girth welds with different defects should be repaired and/or replaced. The paper introduces a full-scale pipeline investigation program. Fatigue and burst tests were executed on repaired pipeline sections containing artificial surface and through-wall defects, modelling gouges and leakages, respectively. Both separate and interacting flaws were investigated. Different composite reinforcing methods, in other words wrap systems, were applied, investigated and compared. Furthermore, long-term operated and cut gas transporting pipeline sections containing girth welds were investigated, too. The testing results and the damage histories were compared with each other; safety factor was defined and calculated for the assessment of the effectiveness of the reinforcing systems and the reliability of the girth welds.
查看更多>>摘要：? 2022 Elsevier LtdThis work aimed to analyze a failure that occurred on the TP347H reheater tube in a supercritical circulating fluidized bed boiler from a thermal power plant. Optical microscopy (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), electron probe micro-analysis (EPMA), digital microhardness tester (DMT), X-ray fluorescence spectroscopy equipment (XRF), and carbon sulfur analyzer (CSA) were used to characterize the failed tubes. The results show that the cracks originated in the heat-affected zone and simultaneously propagated in the circumferential and radial directions. There is a multilayered structure in the crack under the effect of the thermal cycle and preferential oxidation. The failure mechanism was identified as stress corrosion cracking (SCC). The cracks were produced under the combined effects of the tensile stress and the high-temperature flue gas environment. Related improvement measures have been implemented to prevent further failures.
查看更多>>摘要：? 2022 Elsevier LtdThe aircraft industry is a leading industry in terms of the implementation of new materials and technologies. In the development of a light aircraft several different materials were considered for the engine cover design and the final decision was to select a composite material. Part of the research performed on the cover design is presented in this paper. The composite test specimens were produced and mechanical properties were investigated in the tensile and three-point flexural tests according to the required standards. The comparison of experimentally and numerically obtained mechanical properties showed good agreement, which led to the design, verification and manufacturing of the complex-shaped engine cover without costly and demanding tests. It was considered that numerical simulations of the engine cover performance under different loading conditions yielded realistic results, therefore experimental verification was excluded. The flight tests proved the predicted behavior, thus verifying the design methodology presented in this paper.
查看更多>>摘要：? 2022 Elsevier LtdCasing deformation is often encountered due to hydraulic fracturing in the unconventional reservoir. Analysis of 3D seismic, microseismic and logging data shows that the casing shear failure is the primary casing failure mode during hydraulic fracturing. The casing deformation is closely related to the fracture system near the wellbore, but the mechanism and law behind this phenomenon are not completely clear. The slip mechanism of the fracture system and the characteristics of casing deformation were investigated to prevent casing deformation and identify the fracture with large slip distance. Based on the Mohr-Coulomb and maximum circumferential stress theory, the slip mode of natural fracture and the slip mechanism of artificial fracture were analyzed, respectively. Then, two numerical models were established to calculate the slip distance with finite fracture height and corresponding casing deformation. Furthermore, a monitoring model of casing deformation was presented based on microseismic data and real-time injection parameters. The result shows three slip modes in the fracture system crossing wellbore under different fluid pressures, including shear-slip under low fluid pressure, open-slip under medium fluid pressure and propagation-slip under high fluid pressure. The slip distance is associated with fracture length, fracture height, fluid pressure in the fracture and fracture angle. Hydraulic fracturing not only activates natural fractures and faults but also causes the slip of artificial fractures created by hydraulic fracturing, which is responsible for the casing shear deformation after fracturing and during production. The greater the stress deflection angle, the longer and higher the artificial fracture, the more likely the casing deformation in the fracturing section. Therefore, the scale of artificial fracture should be controlled during hydraulic fracturing. This study will provide guidance for predicting fracture slip distance and casing deformation prevention.
查看更多>>摘要：? 2022 Elsevier LtdAs the key component of gas-insulated switchgear (GIS), O-ring samples withdrawn from the long-term field aging conditions were of vital importance in the study of their performance. This article collected several serviced EPDM and CR GIS O-rings operated for 8, 9, 18, 25 and 30 years from power substations located at different sites. The two EPDM samples were withdrawn from the fault phase and non-fault phase respectively, during the emergency repair of a trip-out accident. The samples studied were cut into parts and analyzed from their air side and SF6 side by SEM, EDS and FTIR to observe their surface morphology, element migration and carbonyl absorbance. Deformation recovery ratio was proposed as useful index to characterize the recover ability of the serviced GIS O-ring samples. With some simple assumptions, the degradation of CR O-rings was estimated as a 9.6-order reaction.
查看更多>>摘要：? 2022 Elsevier LtdMain entries in some underground coal mines are tunneled into coal seams. During coal mining, main entries usually have a one-side gob or two-side gobs. Serious coal bursts have occurred in the isolated main entry area (IMEA). In this study, coal bursts in the IMEA are investigated. A large-scale numerical model is built to depict the static-dynamic stress evolution in the IMEA. Likewise, the study discusses the coal burst mechanism in the IMEA and proposes the measures to decrease the coal burst risk. During tunnelling of the main entry, coal bursts in the IMEA occur in the intersection of roadways. During coal mining, coal bursts mainly arise in the area between the gobs on both sides. Coal bursts in the IMEA are induced by high static and low dynamic stress. When coal is mined, the abutment stress around the gobs on both sides transfers to deeper regions and intersects in the IMEA, leading to higher static stress in coal mass. The seismic-based dynamic stress negatively correlates to the distance between the seismic sources and the IMEA. During coal mining, dynamic stress fluctuates, then the amplitude decreases and finally remains at a low value and exerts slight dynamic disturbance on the IMEA. When static stress is low, only higher dynamic stress can lead to coal bursts. However, when static stress is high, low dynamic stress can induce coal bursts. Coal bursts in the IMEA are caused by the superposition of high static stress in coal seam and low seismic-based dynamic stress disturbance from longwall panels. Roof blasting in the IMEA and roof pre-splitting blasting in longwall panels are proposed and implemented on site. Field monitoring results indicate that the de-stressing measures significantly decrease the coal burst risk in the IMEA.
查看更多>>摘要：? 2022 Elsevier LtdThe performance degradation of composite materials under fatigue loading is so complex that the present knowledge is far from complete. This study aims to present a pair of residual strength and residual stiffness models based on a unified fatigue damage formula, and predict fatigue life under variable amplitude cyclic loading. Firstly, a unified fatigue damage model for composite materials is proposed, which is capable of characterizing fatigue damage development caused by strength degradation and stiffness degradation, respectively. Subsequently, a pair of residual strength and residual stiffness models is presented to estimate the performance degradation of composite materials. Finally, the corresponding life prediction methods are developed from the viewpoints of strength degradation and stiffness degradation, respectively. A set of experimental data for composite laminates are utilized to validate the proposed models and methods. The results show that the proposed residual strength and stiffness models are flexible enough to fit strength and stiffness degradation data with good agreement. Moreover, the developed life prediction methods are capable of calculating fatigue life of composite laminates with high accuracy.
查看更多>>摘要：? 2022 Elsevier LtdIn this study, the failure modes of a blast furnace tuyere after service damage were systematically investigated. The high ambient temperature caused grain growth and hardness reduction at the front end of the tuyere. Owing to scraping by gyratory coke in the blast furnace, a perforation formed at the front end of the tuyere, causing damage. Owing to the uneven distribution of components caused by repair welding, cracks occurred in the front coating of the inner wall of the tuyere. The wear of the inner wall of the tuyere was related to the angle and depth of the coal injection gun, and the wear mechanism differed at different positions. Thus, tuyere failure is mainly attributed to the wear of the front end and inner wall. Therefore, it is necessary to develop a coating with excellent high-temperature wear resistance to protect the inner wall and the front end of tuyeres, thereby extending their service life.
查看更多>>摘要：? 2022 Elsevier LtdThis research examined the surface and internal structure of lattice samples with the use of computed tomography. The CAD system PTC Creo Parametric 8 was used to create a 3D model of a lattice structure. For research within this paper, two samples of ABS building material were produced with the use of FDM technology. One of them was destructively tested, i.e., deformed by pressure. The untested sample contained, in addition to base material, P400SR supporting material while the tested sample only contained ABS construction material. Individual samples were subjected to microCT scanning to perform samples' analysis of dimensional and shape characteristics and their porosity. The paper describes the procedure and methodology of individual problem-solving steps. Our basic requirement was to determine surface for software reconstruction as it affects all analyzes being performed. Since the unloaded sample also contains support material, the surface area for the base material only had to be determined and support material, while reconstructing the sample, be removed. Due to higher support material density, direct segmentation of base material was impossible. In the end, the porosity analysis of samples was created with the use of VGStudio MAX software.
NSTL
Elsevier