Failure analysis of the brass tubes in a lubricating oil cooler

Failure analysis was carried out on leaked brass tubes of a lubricating oil cooler. Direct evidences of dezincification and stress corrosion cracking (SCC) were observed by scanning electron microscope (SEM) and energy dispersive spectroscopic (EDS) analysis. It is found that there are many small pits distributed on the fracture surface and EDS analysis revealed the occurrence of dezincification in the small pits. SCC was observed on the cross-sectional plane of the fracture by SEM. Ammonia test has proved the existence of residual stress in the as-received tubes. It is determined that the brass tubes have been suffered from the co-action between dezincification and SCC.     

pH值对7050铝合金膜致应力和应力腐蚀敏感性的影响

采用慢应变速率拉伸法和流变应力差值法研究了7050铝合金在3.5%(质量分数)NaCl水溶液中膜致应力和应力腐蚀敏感性随pH值的变化规律。结果表明:当pH≤7时,随着pH值的增大,膜致应力和应力腐蚀敏感性均下降,当pH7时,膜致应力和应力腐蚀敏感性随着pH值的增大而提高;而当pH=1,14时,腐蚀的类型为剥蚀,合金基体发生剥落,表面没有钝化膜产生。pH值在6~9之间时,膜致应力随pH的变化比较平缓,而pH在2~5和10~13之间时,膜致应力变化则较为剧烈,整体的变化曲线呈山谷形。膜致应力和应力腐蚀敏感性具有很强的相关性。XPS研究表明,膜致应力值与钝化膜的成分有关。     

氢气在配位聚合中的作用

氢气作为配位聚合有效的链转移剂被广泛的应用于聚烯烃工业生产中用以调节聚合物的相对分子量,除此之外,氢气还能导致催化剂活性的改变,对于不同的反应体系,对聚合速率有着一定的影响。同时,氢气对聚合物的等规度也产生影响。     

Effect of hydrogen on stress corrosion cracking of copper

The effects of hydrogen on electrochemical behavior and susceptibility of stress corrosion cracking (SCC) of pure copper were studied. SCC susceptibility of pure copper in a 1 M NaNO₂ solution was increased by pre-charged hydrogen. The effect of hydrogen on the susceptibility is more obvious in the low stress region due to the longer fracture time, which resulted in a longer time for more hydrogen to diffuse toward the crack tip. Synergistic effects of hydrogen and stress on corrosion and SCC processes were discussed. The results showed that an interaction between stress and hydrogen at the crack tip could increase the anodic dissolution rate remarkably.     

高钢级管线钢外部应力腐蚀开裂风险因素研究

目前涉及到3个及以上风险因素的管线钢应力腐蚀研究还较少。为此,通过混合水平的正交试验法,采用慢拉伸试验研究了钢级、保护电位、温度、土壤环境等各敏感因素对高钢级管线钢应力腐蚀开裂行为的影响权重,并采用扫描电镜(SEM)观察了-1 500 mV(vs CSE)保护电位下高钢级管线钢在近中性和高pH值模拟土壤溶液中的应力腐蚀行为。研究结果表明:管线钢外部应力腐蚀开裂风险在设置的试验水平因素中,保护电位对应力腐蚀指数I_SSRT影响的权重最大,随后依次是温度、钢级及土壤环境;保护电位-1 500 m V下,X70、X80管线钢在近中性和高p H值模拟土壤溶液中均具有较强的应力腐蚀敏感性,其SCC机制均为氢脆(HE)机制。     

Stress Corrosion Cracking of Pipeline Steels

This paper provides a review of the differences between high pH and near-neutral pH stress corrosion cracking of pipeline steels,influencing factors,and mechanisms.The characteristics and historical information on both forms of SCC are discussed.The prospect for research in the future is also presented.     

氢对钛合金的影响

介绍了钛合金的基本性质,分析了钛合金氢脆机理及表现,概括了氢对钛合金裂纹扩展速率和疲劳寿命的影响,总结了氢致裂纹的影响因素。     

7xxx系铝合金氢脆的研究现状及发展趋势

全面评述了7xxx系铝合金氢脆(HE)问题的国内外研究现状,讨论了氢脆机理以及氢脆的影响因素,并介绍了几种重要的测试方法.针对目前研究工作中尚未从理论上揭示氢脆本质这一突出问题,指出了今后7xxx系铝合金氢脆问题的研究方向,同时结合前期的研究工作,提出了具体的相关建议.     

Effect of Interstitial Hydrogen on Cohesive Strength of Al Grain Boundary with Mg Segregation

The effect of interstitial hydrogen on the cohesion of the Al ∑ =11（113） grain boundary （GB） is investigated based on the thermodynamic model of Rice-Wang using the first-principles density tunction calculation. I he results indicate that interstitial H behaves as an embrittler from ＂strengthening energy＂ analysis. The reduced GB cohesion due to the presence of H at the GB is attributed to the low affinity between H and Al, and the weakened bonding of Al atomic pairs perpendicular to GB plane.     

7B04铝合金应力腐蚀敏感性研究

利用慢应变速率拉伸应力腐蚀实验方法研究7B04铝合金的应力腐蚀开裂敏感性。研究温度、腐蚀介质、电化学极化对应力腐蚀敏感性的影响,结果表明:随温度的升高7B04铝合金的应力腐蚀开裂敏感性增强;溶液的腐蚀性越强,7B04铝合金的应力腐蚀开裂敏感性越大;无论是阳极极化还是阴极极化都会增加7B04铝合金的应力腐蚀开裂敏感性。     

Effect of δ Phase on Hydrogen Embrittlement of Inconel 718 by Notch Tensile Tests

The effect of δ phase on the hydrogen embrittlement (HE) sensitivity of Inconel 718 was investigated by conducting notch tensile tests. Notch tensile specimens with various precipitation morphologies of δ phase were prepared with different heat treatments, and hydrogen was charged into the tensile specimens before tensile tests via a cathodic charging process. The loss of notch tensile strength (NTS) due to the charged hydrogen was used to evaluate the hydrogen embrittlement sensitivity. The results show that δ phase has deleterious effect on NTSs, and the fracture of hydrogen-charged specimens initiated near the notch surfaces. The loss of NTS caused by precharged hydrogen can be greatly decreased by dissolving δ phase. δ-free Inconel 718 alloy is proposed for the applications in hydrogen environments.     

Performance of Amperometric and Potentiometric Hydrogen Sensors

The principle, design, construction and performance of the amperometric and potentiometric sensors for measuring the permeation rate of hydrogen through the wall of metal equipment were investigated in order to develop a new type of hydrogen sensor with high accuracy. The transient curves of hydrogen permeation under a given charging condition were employed to evaluate the performance of two types of hydrogen sensors. The relative deviation of the hydrogen concentration detected with two types of sensors under the same condition varied from 3.0% to 13%. The accuracy, response time, reproducibility, and installation were discussed and compared. Response time of the potentiometric sensor （E-sensor） was shorter than that of the amperometric sensor （I-sensor）. Both types of sensors exhibited good reproducibility. Development of I-sensor composed of a kind of proton conductor adhesives or non-fluid electrolytes which contain two functions of high electrical conductivity and a strong adhesion will be a promising prospect in order to measure hydrogen permeation at high temperature.     

Effect of δ Phase on Hydrogen Embrittlement of Inconel 718 by Notch Tensile Tests

The effect of δ phase on the hydrogen embrittlement (HE) sensitivity of Inconel 718 was investigated by conducting notch tensile tests. Notch tensile specimens with various precipitation morphologies of δ phase were prepared with different heat treatments, and hydrogen was charged into the tensile specimens before tensile tests via a cathodic charging process. The loss of notch tensile strength (NTS) due to the charged hydrogen was used to evaluate the hydrogen embrittlement sensitivity. The results show that δ phase has deleterious effect on NTSs, and the fracture of hydrogen-charged specimens initiated near the notch surfaces. The loss of NTS caused by precharged hydrogen can be greatly decreased by dissolving δ phase. δ-free Inconel 718 alloy is proposed for the applications in hydrogen environments.     

Application of Hydrogen Peroxide as an Environmental Stress Indicator for Vegetation Management

Adaptive vegetation management is time-consuming and requires long-term colony monitoring to obtain reliable results. Although vegetation management has been widely adopted, the only method existing at present for evaluating the habitat conditions under management involves observations over a long period of time. The presence of reactive oxygen species (ROS) has long been used as an indicator of environmental stress in plants, and has recently been intensely studied. Among such ROS, hydrogen peroxide (H₂O₂) is relatively stable, and can be conveniently and accurately quantified. Thus, the quantification of plant H₂O₂ could be applied as a stress indicator for riparian and aquatic vegetation management approaches while evaluating the conditions of a plant species within a habitat. This study presents an approach for elucidating the applicability of H₂O₂ as a quantitative indicator of environmental stresses on plants, particularly for vegetation management. Submerged macrophytes and riparian species were studied under laboratory and field conditions (Lake Shinji, Saba River, Eno River, and Hii River in Japan) for H₂O₂ formation under various stress conditions. The results suggest that H₂O₂ can be conveniently applied as a stress indicator in environmental management.     

氢对位错运动的影响

金属材料氢脆的根本原因是氢对位错运动、分布和结构的影响。本文利用透射电镜观察了渗氢与未渗氢试样中的形变亚结构。结果表明氢促进了位错的平面滑移 ,阻碍了交滑移 ,从而加剧位错塞积 ,导致位错分布和塑性变形的不均匀性。文中提出了几种形变亚结构特征的形成机制 ,并进一步讨论了氢影响位错运动的物理原因。     

国产管线钢的环境开裂性能研究

采用电化学测试和慢应变速率实验(SSRT)研究了国产X70管线钢在近中性pH和高pH溶液中的应力腐蚀破裂(SCC)行为.结果表明,X70钢在高pH溶液和近中性pH溶液中的阳极极化曲线表现出明显的差异:在高pH溶液中有明显的活化-钝化转变而在近中性pH溶液中则无;在近中性pH溶液中,X70管线钢的开裂模式是穿晶型的,具有准解理特征,并且随着外加阴极电位的降低,SCC敏感性增加,氢致破裂占主导;随温度的下降以及溶液中CO2含量的增加,溶液pH值降低,SCC敏感性增加.在高pH溶液中,在阴极极化时,X70钢表现出与在近中性pH溶液中类似的破裂行为和特征,即SCC敏感性随电位降低而增大,裂纹数目少而大,裂纹易扩展;但在阳极极化时,裂纹数目多而小,易萌生但难扩展.在2种溶液中阳极极化时,均存在SCC敏感电位区.     

The Effect of History on Hydrogen Assisted Cracking: 2. A revision of K-dominance

In Part 1 of this work it was shown that, because of the coupling of the processes of crack growth and hydrogen accumulation in rupture sites, the crack growth kinetics curve v= v(K) in hydrogen assisted cracking (HAC) does not possess intrinsic uniqueness as a material's characteristic curve. This paper presents an analytical treatment of the phenomenon and a special regime of steady-state crack growth is seen to exist for which hydrogen assisted cracking turns out to be a K-dominated process. The corresponding plot of the steady-state v against K acquires the uniqueness of a material's characteristic curve which may be used in engineering to provide more conservative evaluation of material resistance and structural integrity in HAC conditions. Inherent uncertainties in the customary fracture mechanics approach to HAC are analysed in an attempt to guide the way towards its further refinement. On leave from: Pidstryhach Institute of Applied Mechanics and Mathematics, Lviv, Ukraine This revised version was published online in August 2006 with corrections to the Cover Date.     

A Review of Technical Advances,Barriers, and Solutions in the Power to Hydrogen (P2H) Roadmap

Power to hydrogen (P2H) provides a promising solution to the geographic mismatch between sources of renewable energy and the market, due to its technological maturity, flexibility, and the availability of technical and economic data from a range of active demonstration projects. In this review, we aim to provide an overview of the status of P2H, analyze its technical barriers and solutions, and propose potential opportunities for future research and industrial demonstrations. We specifically focus on the transport of hydrogen via natural gas pipeline networks and end-user purification. Strong evidence shows that an addition of about 10% hydrogen into natural gas pipelines has negligible effects on the pipelines and utilization appliances, and may therefore extend the asset value of the pipelines after natural gas is depleted. To obtain pure hydrogen from hydrogen-enriched natural gas (HENG) mixtures, end-user separation is inevitable, and can be achieved through membranes, adsorption, and other promising separation technologies. However, novel materials with high selectivity and capacity will be the key to the development of industrial processes, and an integrated membrane-adsorption process may be considered in order to produce high-purity hydrogen from HENG. It is also worth investigating the feasibility of electrochemical separation (hydrogen pumping) at a large scale and its energy analysis. Cryogenics may only be feasible when liquefied natural gas (LNG) is one of the major products. A range of other technological and operational barriers and opportunities, such as water availability, byproduct (oxygen) utilization, and environmental impacts, are also discussed. This review will advance readers’ understanding of P2H and foster the development of the hydrogen economy.     

甲酸钠尾气吸收塔失效分析

采用扫描电镜观察、力学性能检测、化学成分分析和残余应力测定等方法系统分析了甲酸钠尾气吸收塔发生泄漏的原因。结果表明：泄漏部位的腐蚀产物含有钠、氯等元素,同时泄漏部位存在残余应力偏高问题,在不断遭受腐蚀和工作应力的共同作用下产生应力腐蚀开裂,最终导致设备的失效。     

On the Effect of Stress Triaxiality on Void Coalescence

Failure of ductile materials is often related to coalescence of microscopic voids. The stress triaxiality is one of the primary factors that influence the coalescence. In the present work, a 3D unit cell model is employed to investigate this effect. The cell model contains two aligned voids. A coalescence criterion is proposed in which the critical void volume fraction is expressed in terms of stress triaxiality.