Stress corrosion crack initiation in Alloy 690 in high temperature water

Initiation of stress corrosion cracks in Alloy 690 in high temperature water is a rare occurrence and depends on the method by which the sample is loaded. Only in dynamic straining experiments is crack initiation consistently observed. Stress relaxation in constant deflection tests, and lack of a means of rupturing the oxide film in constant load tests are the principle reasons for the difficulty of initiating cracks in these tests. These observations, combined with those from the much more susceptible Alloy 600 form the basis for a mechanism stress corrosion crack (SCC) initiation of Alloy 690. SCC initiation is proposed to occur in three stages: an oxidation stage in which a protective film of Cr₂O₃ is formed on the surface over grain boundaries, an incubation stage in which successive cycles of oxide film rupture and repair depletes the grain boundary of chromium, and a nucleation stage in which the chromium depleted grain boundary is no longer able to support growth of a protective chromium oxide layer, resulting in formation and rupture of oxides down the grain boundary. The mechanism is supported by the available literature on oxidation and crack initiation of Alloy 690 in hydrogenated primary water conditions.     

Effects of dissolved oxygen on corrosion fatigue cracking of Alloy 690(TT) in pressurized water reactor environments

Alloy 690(TT) is widely used for steam generator tubes in pressurized water reactor (PWRs), where it is susceptible to corrosion fatigue. In this study, the effects of dissolved oxygen on the corrosion fatigue cracking behavior of Alloy 690(TT) in simulated PWR environments were investigated under small scale yielding conditions. Dissolved oxygen, combined with the monotonic plastic zone size (r_p), had a significant influence on out-of-plane cracking of corrosion fatigue crack and environment factor (F_en).     

Effect of temperature on corrosion behavior of alloy 690 in high temperature hydrogenated water

The influence of temperature on the corrosion behavior of Alloy 690 is evaluated using potentiodynamic polarization curves,electrochemical impedance spectra(EIS),scanning electron microscopy(SEM),Xray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM).The corrosion rate of Alloy 690 reaches a local maximum at 250?C.The kinetic control step of the growth of oxide film changes from the diffusion process of aqueous-phase ions to the growth of Cr-rich barrier layer in the temperature range of 200–300?C.A modified double-layer model is proposed to describe the effect of temperature on the structure and composition of the oxide film.     

Effects of thiosulfate and dissolved oxygen on crevice corrosion of Alloy 690 in high-temperature chloride solution

The crevice corrosion behavior of Alloy 690 was investigated in high-temperature chloride solution containing different concentrations of thiosulfate(S₂O₃^2-) and dissolved oxygen(DO). The S2O32- inhibited corrosion of Alloy 690 through consuming oxygen in aerated chloride solution. In deaerated chloride solution,the S₂O₃^2- was reduced to S° and S^2- and subsequently incorporated into the oxide films, which promoted the pitting corrosion at locations of both TiN inclusions and matrix inside the crevice during the crevice corrosion as well as influenced the composition and thickness of the oxide films. The effect mechanisms of S₂O₃^2- and DO on crevice corrosion in high-temperature chloride solution are discussed.     

High precision device for reproducing concentration units for oxygen dissolved in water

Measurement Techniques - A high precision device for reproducing concentration units for oxygen dissolved in water and its operating principles are described. Results are given for studies of the...     

The influence of high temperature ageing on the Structure of Alloy 800

The report presents investigations of the microstructure of commercial Alloy 800 after isothermal ageing at 900°C, carried out by optical microscopy and by transmission electron microscopy using replica and thin foil techniques. The high temperature ageing was characterized predominantly by precipitation of carbides on grain and twin boundaries of the austenitic matrix, as well as on dislocations within the grains. The carbides were identified, using electron microscope diffraction and X-ray phase analysis of electrolytic extractions, as (Cr, Fe)₂₃C₆, Ti (C, N) and TiC.     

膜接触器除氧实验研究及其传质分析

采用疏水性聚丙烯中空纤维膜组件作为膜接触器,主要考察了水流量、真空度以及水温对水中溶解氧的去除效率友其传质性能的影响,同时考察了膜接触器长期运存后引起的膜污染问题并对此时的污染膜阻力及总传质阻力做了定量的计算.实验结果表明,在适当的操作条件下,膜接触器能得到较理想的除氧效果.除氧效率和膜传质系数变化规律具有良好的对应关系.     

Role of apex oxygen and redox elements in high temperature superconductors

The presence of valence fluctuating redox ions such as Pb, Tl, Sb, etc can enhance the transition temperature of the new oxide superconductors. We propose the possibility of the existence of negative Hubbard parameter (U) on redox ion which results in effective negativeU on apex oxygen bridging redox ion and the CuO₂ planes. This enhancesT _c .     

Effect of oxygen dissolved in metal on the strength of Silver-Alumina junctions formed in the solid state

In this study, the strength of the junctions formed by thermal compression of solid silver and alumina is measured using an indirect tensile test. The essential role of the oxygen content in solid solution of metal on the adherence force is particularly highlighted. Our results are analyzed starting from the surfactant effect of oxygen, in solid solution of metal at the interface Ag/Al₂O₃. It’s clearly shown that an unfavourable couple (weak energy of adhesion) can have an interesting behaviour if the beneficial role of certain elements of additions is taken into account. It is also shown that strong junctions can be obtained while exploiting the initial preparation of metal.     

Recombination of atomic oxygen on sintered zirconia at high temperature in non-equilibrium air plasma

High temperature ceramic materials are necessary for the design of primary heat shields for future re-usable space vehicles re-entering atmospheric planet at hypersonic velocity. During the re-entry phase on earth, one of the most important phenomena occurring on the heat shield is the recombination of atomic oxygen and this phenomenon is more or less catalyzed by the material of the heat shield.     

Microstructural modelling of grain-boundary stresses in Alloy 600

The stress distribution in a random polycrystalline material (Alloy 600) was studied using a topologically correct microstructural model. The distributions of von Mises and hydrostatic stresses, which could be important factors when studying the intergranular stress corrosion cracking, at the grain vertices were analysed as a function of microstructure, grain orientations and loading conditions. The grain size, shape, and orientation had a more pronounced effect on stress distribution than the loading conditions. The stress concentration factor was higher for hydrostatic stress (1.7) than for von Mises stress (1.5). Hydrostatic stress showed more pronounced dependence on the disorientation angle than von Mises stress. The observed stress concentration is high enough to cause localized plastic microdeformation, even when the polycrystalline aggregate is in the macroscopic elastic regime. The modelling of stresses and strains in polycrystalline materials can identify the microstructures (grain-size distributions, texture) intrinsically susceptible to stress/strain concentrations and justify the correctness of applied stress state during the stress corrosion cracking tests.     

A pilot study on wastewater treatment by constructed wetlands with high dissolved oxygen vegetated submerged bed

It is necessary to treat wastewater in a more environmentally friendly fashion, vegetated submerge bed constructed wetlands (CWs) has become the focus of the research in this field. In this paper, the overall capacity of vertical subsurface flow CWs in the removal of pollutants from municipal wastewater effluent and the effects of the depth of vegetated submerged bed on the removal efficiency were studied. The results showed that the COD, NH4+-N and TN could be removed effectively in the vertical subsurface flow CWs, the best efficiency was obtained from the 10 cm run. However, the TP removal was not effective in all vertical CWs. A shallow depth of vegetated submerged bed may avoid the risk of substrate plugging effectively, and may keep a stable operation of CWs in long term. Decreasing the depth of vegetated submerged bed could create a sufficient aerobic circumstance in which the concentration of DO in bed was super saturation.     

Expansive concrete cured in pressurized water at high temperature

Behaviours of expansive concretes cured in pressurized water at high temperature (TPC curing) are investigated with regard to their variations in strain, weight and strength. These behaviours are compared with those cured by autoclave curing (AC curing) at the same pressure and temperature. The experimental data show that both of these curing methods are effective in reducing autogenous shrinkage and drying shrinkage at longer age after the curing. Particularly when TPC curing is adopted, the required expansion of concrete can be attained at smaller dosage of expansive agents, and after the curing length changes due to hygrometric or hygroscopic conditions are almost eliminated for later age. Therefore, this curing method is anticipated to be effective in introducing chemical prestress in a reinforced concrete member, which is proved by loading tests of spirally reinforced pipe specimens [Ei.-i. Tazawa, K. Miyaguchi, in: Proceedings of the 25th JUCC Congress on Cement and Concrete, 1998, pp. 71–76].     

Effect of dissolved oxygen concentration on nitrate removal from groundwater using a denitrifying submerged filter

A unidirectional submerged filter system was employed to purify groundwater contaminated with nitrate by biological denitrification. The influence of the concentration of dissolved oxygen (DO) in the process was tested using ethanol, methanol and sucrose as carbon sources. Inorganic-nitrogen removal, growth of the biofilm, platable denitrifying bacteria and nitrate reducing bacteria in biofilm were studied. With regard to the type of electron donor used, the presence of oxygen decreased the removal efficiency of inorganic nitrogen and caused an increase of nitrite concentration in the treated water. These negative effects depended on utilised carbon source. Biological denitrification with alcohols such as ethanol and methanol was less affected by DO than with sucrose. The development of the biofilm was also influenced by the DO concentration as excess O₂ caused reduced biofilm growth. These biofilms developed in oxygen presence had a smaller bacterial density and a lower denitrifying bacteria versus nitrate reducing bacteria ratio, which led to an unfavorable inorganic nitrogen removal and presence of nitrite in the treated water. All these effects are more pronounced when sucrose is used as carbon source.     

Effect of dissolved oxygen on electrochemical corrosion behavior of 2205 duplex stainless steel in hot concentrated seawater

The corrosion behavior of 2205 duplex stainless steel was investigated in hot concentrated seawater with different dissolved oxygen(DO) concentration by electrochemical measurement techniques and surface analysis methods. DO obviously enhances the cathodic reaction process, the formation of passive film and polarization resistance. With increasing the DO concentration from 0.34 to 3.06 mg L^-1, the relative contents of Fe₂O₃ and Cr₂O₃ and the Cr-enrichment gradually enlarge in the passive film. The higher DO concentrations result in lower defect densities and thicker of space charge layers in the passive films,whichmayeffectively inhibit the intrusion of aggressive chloride ions. The increment inDOconcentration clearly increases the pitting potential, but decreases the repassivation potential. It may weaken both the occurrence and repassviation tendencies of stable pitting corrosion.     

Ti600钛合金的氧化行为

研究了Ti600钛合金在700-1000℃范围内的氧化行为.结果表明,Ti600的100 h氧化动力学近似遵循抛物线-直线规律,氧化激活能为224 kJ·mol-1.Ti600试样在700℃氧化100h后其表面形成了致密的氧化皮,而在高于700℃氧化100 h后氧化皮出现多层结构并开始剥落,氧化皮主要由金红石型TiO2...     

The effect of high temperature carburization upon the ambient temperature ductility of Alloy 800H

This paper presents the results of a series of tests designed to assess the changes in ambient temperature ductility of Alloy BOOH, a 20%Cr-32%Ni austenitic steel, resulting from exposure to an aggressive carburizing environment at 10000°C. A gas mixture of H₂-CH₄ with 0.8 carbon activity has been used as the corrosive medium and postexposure compression testing of the carburized tubular specimens has enabled the significant reduction in ductility accompanying the uptake of carbon to be demonstrated and understood.     

加工工艺对Ti600合金棒材性能的影响

通过对精锻、自由锻、旋锻及热轧4种加工方式获得的Ti600合金棒材在3种不同的热处理制度下进行处理,再测试室温拉伸性能及蠕变性能,研究不同加工工艺对Ti600合金棒材性能的影响.研究结果表明,在同一种热处理制度下,加工工艺对材料的室温拉伸性能及蠕变性能并无太大影响,但是4种工艺加工的棒材在1 060℃,1 h,AC+650℃,8 h,AC都具有较低的室温塑性,而在1 005℃,1 h,AC+650℃,8 h,AC虽具有好的室温塑性但抗蠕变性能较差.只有经过1 020℃,1 h,AC+650℃,8 h,AC处理,才能使其室温性能与蠕变性能获得良好的匹配.