Evaluation of hydrogen induced cracking behavior of API X70 pipeline steel at different heat treatments

The microstructure of API X70 pipeline steel was modified by applying different heat treatments including water-quenched, water-sprayed, and water-quenched and tempered. Hydrogen induced cracking behavior was investigated on the X70 steel at these heat treatments. Two test methods, Japanese Industrial Standard (JIS) and vacuum thermal desorption, were used to release hydrogen from reversible and irreversible traps. The experimental results showed that the highest amount of discharged hydrogen in reversible and irreversible traps was related to the water-sprayed and as-received steels. The hydrogen discharged content from reversible traps reached to a saturation level after 8 h of charging, and it decreased considerably when the steels were charged for 15 h and 24 h. Hydrogen discharge tests proved that a higher amount of hydrogen inside steel is not a reliable measure for HIC evaluation. HIC test results also document that the water-quenched steel with agglomerated martensite particles had the highest susceptibility to HIC. Texture study results show that a low fraction of important texture components, such as {023}, {321} and {332}, cannot be reliably used to evaluate HIC. As a result, a novel method of manufacturing of pipeline steels with an optimized texture is required to increase safety and reliability of transportation of sour gas and oil.     

Fabrication of gradient C/C-SiC-MoSi2 composites with enhanced ablation performance

C/C-SiC-MoSi₂ composites with gradient composition and microstructure were prepared by a novel vacuum filtration infiltration (VFI) process with a later hydrothermal densification. The composition distribution, microstructure, density, porosity, thermal conductivity and ablation properties of the composites were investigated. Results show that the distributions of SiC and MoSi₂ are homogeneous and gradient along the cross-section of the composites, respectively. From the inner part to the outer part of the composites, the increase in density and thermal conductivity is achieved. The outer part of the composites exhibits enhanced ablation performance. After being exposed to the oxyacetylene flame at 2000 °C for 30 s, the linear and mass rates of the as-prepared composites are only 0.0051 mm/s and 0.76 mg/s.     

Influence of remelting on microstructure,hardness and corrosion behaviour of AlCoCrFeNiTi high entropy alloy

Abstract

High entropy alloys are a newly developed class of alloys, which tend to form a single solid solution or a mixture of solid solutions with simple crystal structures. These alloys possess excellent mechanical properties, thermal stability and corrosion resistance. In the present paper, an AlCoCrFeNiTi high entropy alloy was obtained by induction melting, and the influence of the remelting process on the mechanical and corrosion resistance characteristics of the alloy was investigated. Thus, optical and scanning electron microscopy revealed less phase segregation and a fine dendritic structure for the remelted alloy, while corrosion tests indicated that present alloy, in remelted state, has better corrosion resistance than as cast alloy and stainless steel. The Vickers microhardness measurements demonstrated an improvement of the alloy microhardness by remelting process due to the decrease in phase segregation and the increase in dendrite refinement level.     

微电子领域中陶瓷劈刀研究与应用进展

综述了陶瓷劈刀的研究与应用进展,主要包括陶瓷劈刀的成分、结构、工作过程、质量缺陷、应用领域,特别是在微电子领域中的应用,重点评述了当前陶瓷劈刀在制造新工艺和运用方面存在的主要问题,指出寻找制造陶瓷劈刀的新材料和改进陶瓷劈刀的成型工艺是目前陶瓷劈刀的研究重点,并提出了陶瓷劈刀今后的发展方向。     

真空条件下除湿溶液再生的模拟与实验研究

除湿溶液的高效再生是除湿空调系统运行的重要保障。为研究除湿溶液的再生效率,将真空技术应用于溶液的再生过程,搭建了真空条件下的除湿溶液再生试验台。真空再生罐由低温热水提供所需热量,蒸发的水蒸汽在捕水器中凝结。在一定真空度下,分析了溶质质量分数、热水温度、冷水温度等不同因素对再生性能的影响。以水分蒸发率作为评价指标。实验台操作压力为5kPa,溶质质量分数取值为28%~34%,热水温度区间为56~62℃,冷水温度区间为14~20℃。实验结果表明:溶质质量分数和热水温度对蒸发率的影响较为显著,热水由56℃增加到62℃,蒸发率提高了34.5%。利用混合模型和自定义函数对再生过程进行了数值模拟,模拟结果与实验结果基本吻合。     

高真空多层绝热储罐中微热型复合吸附剂吸附氢气的实验研究

为解决氢气导致高真空多层绝热储罐夹层真空度下降和吸氢剂价格昂贵的问题,本文搭建了吸氢试验台,研究了廉价微热型吸氢剂CuO和CuO+C的吸氢性能;结果表明:C的加入使CuO吸氢活化温度下降了100℃,吸氢速率提高了26.2倍;测定了CuO+C的吸氢等温线,分析了多次吸氢过程,得知在低压时,吸氢产物对吸氢有促进作用,而在高压时,作用不明显;根据BDDT理论,该等温线属于第Ⅰ类吸附等温线,并用Langmuir等温式进行了拟合     

Thermal resistance of Salmonella enterica serovar Anatum on cabbage surfaces during drying: effects of drying methods and conditions

The effects of selected drying methods, i.e., hot air drying, vacuum drying and low-pressure superheated steam drying (LPSSD), on the heat resistance of Salmonella attached on vegetable surface, which are data that have never been reported elsewhere, were investigated at drying temperatures of 50-70 °C; vacuum drying and LPSSD were carried out at an absolute pressure of 10 kPa. The selected Salmonella serovar, i.e., S. Anatum, was used as a test organism. Cabbage was used as a vegetable model to represent uneven natural surface. The results showed that drying methods had a significant effect on the drying kinetics as well as the destruction rate of Salmonella. Higher drying temperatures resulted in higher destruction rates of S. Anatum. Hot air drying was noted to be the slowest drying process, while vacuum drying and LPSSD could be used to shorten the drying time. By considering the reduction in the number of Salmonella at the end of drying, LPSSD is recommended as it has proved to yield the highest degree of S. Anatum inactivation.     

Recovery of volatile fruit juice aroma compounds by membrane technology: Sweeping gas versus vacuum membrane distillation

The influence of temperature (10–45 °C), feed flow rate (300–500 L/h) and sweeping gas flow rate (1.2–2 m³/h) on the recovery of berry fruit juice aroma compounds by sweeping gas membrane distillation (SGMD) was examined on an aroma model solution and on black currant juice in a lab scale membrane distillation set up. The data were compared to recovery of the aroma compounds by vacuum membrane distillation (VMD). The flux of SGMD increased with an increase in temperature, feed flow rate or sweeping gas flow rate. Increased temperature and feed flow rate also increased the concentration factors (C_permeate/C_feed) of the aroma compounds. At 45 °C the most volatile and hydrophobic aroma compounds obtained the highest concentration factors: 12.1–9.3 (black currant juice) and 17.2–12.8 (model solution). With black currant juice a volume reduction of 13.7% (vol.%) at 45 °C, 400 L/h, resulted in an aroma recovery of 73–84 vol.% for the most volatile compounds. Compared to VMD, the aroma recovery with SGMD was less influenced by the feed flow rate but more influenced by the temperature. Higher fluxes were achieved during concentration by VMD and this reduced the operation time, which in turn reduced the degradation of anthocyanins and polyphenolic compounds in the juice.

Industrial relevance

High temperature evaporation is the most widely used industrial technique for aroma recovery and concentration of juices, but membrane distillation (MD) may provide for gentler aroma stripping and lower energy consumption. This study gives important clues about the fate of berry juice aroma compounds and polyphenols during concentration by MD, and identifies the main factors influencing the aroma recovery efficiency with MD. Both SGMD and VMD are promising techniques for gentle stripping of berry juice aroma compounds and deserve further consideration as alternative techniques for gentle aroma stripping in industrial fruit juice processing.