异抗坏血酸稳定亚硫酸盐的制备及其贮存稳定性研究

通过除氧试验和空气氧化试验,研究了异抗坏血酸对亚硫酸盐自动氧化的阻滞作用。结果表明,自由基链反应引发剂铜离子能够加速亚硫酸盐与氧的反应,自由基吸收剂异抗坏血酸能够通过消除亚硫酸盐氧化过程中生成的自由基而抑制反应,水的ｐＨ值、碱度和硬度成份则无影响。试验结果为亚硫酸盐氧化的自由基机理提供了有力的证据,也为亚硫酸盐的贮存失效提供了有效的防止方法。     

低位热力除氧器的几个关键技术问题--中投洁天技术系列报导之三

一、引言 电站锅炉和各种工业锅炉给水的含氧量要求在规定的限度以内,从而减轻锅炉、管网、热设备的氧化腐蚀.一般采用的除氧方法有热力除氧、解析除氧、钢屑除氧、化学药剂除氧等.     

介绍一种新型除氧器

众所周知,锅炉和管道中的氧腐蚀大都属于溃疡型的局部腐蚀。这种腐蚀比均匀腐蚀会更快地使锅炉受压元件或管道因损坏而报废。在热水锅炉系统中,如果管理不善失水过多,会因补给水量太大,使系统和锅炉中带入更多的溶解氧。因此,有时热水锅炉发生的氧腐蚀要比蒸汽锅炉更为严重。锅炉给水除氧工作已刻不容缓。树脂除氧器为量大面广的中小型低压锅炉的给水除氧开辟了新的途径。     

加氧水处理应用于直流炉之基础研究（Ⅱ）：溶解氧对汽机材料抗腐蚀之影响

要把加氧水处理用于日本火电机组的直流炉，首先，必须搞清楚溶解氧对于低压汽机材料的抗腐蚀影响。就溶解氧对于LP转子、叶片材料的应力腐蚀裂纹(SCC)和腐蚀疲劳(CF)方面之影响，加氧水处理委员会进行了研究。研究发现，AVT方式90℃的加氧水条件下，应力腐蚀裂纹(SCC)敏感度不受AVT和加氧水处理之间的水质影响，而且，GE型3．5NiGrMoV钢和GE型12Cr钢的CF试验结果表明，AVT和加氧水处理之间的腐蚀疲劳并没有差别。在3．5NiGrMoV和12Cr钢CF试验中，相同应力水平之下，经过10^10循环次数后，12CrMoV、12GrNlMoV及17-4PH钢不会产生裂纹。LP汽机材料的应力腐蚀裂纹(SCC)和腐蚀疲劳(CF)试验表明，AVT和加氧水处理之间并没有差别。     

真空式除氧器节能效益的探讨

一、概述在热电厂因给水溶氧造成热力设备的腐蚀是一种较为普遍的现象.当热力系统运行时,由于汽水温度较高,氧腐蚀速度加快,再加此种腐蚀具有局部及延续性的特点,对设备危害极大,因此,热电厂均需对给水进行除氧处理.当然,由于热力参数不同,对水质要求也不同,通常是采用真空式除氧,大气热动力除氧,高压除氧等.中小电厂普     

锅炉水射流管道真空水力除氧技术及经济性

一,概述 大庆采油六厂有26座锅炉房,安装8.8台锅炉,总容量为399t/h。每年大修的锅炉中,有30％是因溶解氧的腐蚀而造成的水管穿孔漏水,有些锅炉仅使用2年就因溶解氧的腐蚀使烟管穿孔。溶解氧不仅腐蚀锅炉,对水循环系统也有同样的危害,所造成的损失不亚于锅炉,每年都要维修和更换部分管道与阀门。 随着生产与经济的发展,以及人民生活水平的提高,热水循环保温与采暖的应用越来越多。为降低供热成本,节约资金,锅炉用水的除氧就显得十分重要。把溶解氧降低到国家标准,锅炉寿命将延长4.6倍。换句话说,如果不除氧就要拿出比除氧多大约4.6倍的设备来换取同样的保温与采暖效果。因此锅炉用水除氧是一项十分重要的工作,对节能降耗有着重要的意义。我们采用射流真空水力除氧这一新的除氧技术,除氧效果好,使锅炉由原来的2年大修一次延长到8年大修一次,取得了明显的经济效益。     

热水锅炉内部氧腐蚀情况调查与分析

本文对一百多台烟火管快装炉和带锅筒水管锅炉内部氧腐蚀情况的调查结果进行了分析,分析了产生氧腐蚀的原因,从运行管理和采取除氧措施等方面提出了实用的防氧腐蚀的建议。对锅炉运行管理人员有较大参考价值。     

膜法除氧--锅炉给水除氧新方式

锅炉的腐蚀按腐蚀的机理分为氧腐蚀、酸腐蚀、应力腐蚀等. 当锅炉水不除氧时,氧在水中是强烈的阴极去极化剂,氧气与铁发生化学反应,产生铁的氧化物等,结果是阳极上的铁离子不断转入水中,就造成了氧腐蚀.氧腐蚀在热力设备运行和停运时都会发生.而当水中存在CO2时也能使水中氢离子浓度增加,氢离子也是阴极去极化剂,最后会使阳极上的铁离子不断转入水中,产生常说的酸腐蚀.当水中同时存在O2和CO2时,可使腐蚀加剧.     

运用解吸除氧技术降低锅炉用水的含氧量

在锅炉运行中，氧腐蚀的问题显得格外突出，因氧腐蚀造成的锅炉事故有逐年上升趋势。给水中溶解氧的存在是锅炉发生化学腐蚀和电化学腐蚀的主要因素。GB1576《工业锅炉水质》标准中规定：“锅炉额定功率大于等于4．2MW时，热水锅炉给水应除氧”。但由于除氧方法选择不当或不采取任何除氧措     

热水锅炉的氧腐蚀及除氧措施

近年来，热水锅炉氧腐蚀日趋严重，由此造成的事故时有发生。热水锅炉一般都没有除氧措施，热水锅炉的腐蚀主要由溶解氧含量引起的。我市供热公司的2台直接供热式承压热水锅炉一在江南地区，一在江北地区，仅就氧腐蚀成因、现象及除氧措施简要总结一下。     

Influence of cerium (III) ions on corrosion and hydrogen evolution of carbon steel in acid solutions

This paper intended to investigate the influence of rare earth Ce(III) ions on the corrosion behavior of carbon steel in two acid solutions (0.5 M HCl and 0.25 M H₂SO₄) in order to control the rate of hydrogen evolution in those systems. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were used for corrosion rate and electrochemical impedance evaluation. SEM was used to examine the sample surfaces immersed in acid solutions containing the optimal threshold Ce(III) concentration (0.1 mM). All results reveal that the corrosion resistance of carbon steel in HCl is superior to that in H₂SO₄ due to the higher rate of hydrogen production in the latter. A model for the corrosion process mechanism and inhibition by Ce(III) salt for carbon steel in the two tested media is proposed.     

On the role of hydrogen in the stress corrosion cracking behavior of Q345R steel in HF vapor environment

The stress corrosion cracking (SCC) behavior of Q345R steel in hydrofluoric acid (HF) vapor environment was investigated. It is shown that Q345R has a high susceptibility to SCC in HF vapor environment, which is negatively correlated with the strain rate. Several different crack morphologies and cracking factors are verified: flat cracks in ferrite are associated with anodic dissolution triggered by micro-galvanic corrosion, and porous cracks at the pearlite and pearlite-ferrite interfaces are mainly influenced by hydrogen. The results of hydrogen charging tests show that pre-charging has little effect on the hydrogen embrittlement of Q345R steel, while in-situ charging leads to severe brittle fracture of the material, because hydrogen interacts with large number of moving dislocations generated by in-situ stretching process and penetrates more readily into the material. The synergistic relationship between hydrogen and dislocation motion is found to be the main mechanism for the transition from ductile to brittle fracture.     

Analysis of a carbon composite overwrap pipeline repair system

A relatively new method has been developed to stop external corrosion and structurally reinforce steel pipes by external wrapping of damaged sections using fibre reinforced polymer (FRP) materials. Several different defect geometries representing corrosion patches on steel pipe were characterized using finite-element analysis, by changing the circumferential length of the defect. Pipe vessels containing these defects along with the composite structural repairs were modeled and the results were compared to field tests to determine the effectiveness of the repairs. It was found that the defect width around the circumference had little impact on the ultimate rupture pressure of the repaired vessel, but influenced the stress state in the underlying pipe substrate.     

The effect of nanosized NbC precipitates on electrochemical corrosion behavior of high-strength low-alloy steel in 3.5%NaCl solution

The effect of nanosized NbC precipitates on electrochemical corrosion behavior of high-strength low-alloy (HSLA) steels in 3.5%NaCl solution has been investigated by the means of precipitate modulation, microstructure observation, electrochemical and immersion tests. The results showed that NbC precipitates markedly enhance the corrosion resistance of the H-contained steel, and the mechanism is that the plentiful and highly dispersed nanosized NbC particles acting as massive and effective hydrogen traps play a decisive role in the resistance to hydrogen activated corrosion. Moreover, it is evident that the inhibiting effect is related with the amount, size and distribution of the precipitates, and the optimized microstructures and precipitated phases improve the mechanical properties and resistance to hydrogen activated corrosion of HSLA steel.     

304不锈钢管凝汽器腐蚀原因研究

进行了不锈钢管、水处理药剂和酸洗液的腐蚀性能试验。凝汽器304不锈钢管发生点蚀的主要原因是不锈钢管质量不合格和使用的酸洗液不当。不锈钢酸洗液腐蚀性能的评价不能采用腐蚀失重法。订合同时应写入按照ASTM A249中S7条款检验不锈钢管焊缝质量。     

Corrosion of platinum catalyst in alkaline solutions

The corrosion behavior, as affected by time and potential, of platinum black in alkaline solution at 20 and 70 °C has been studied. It is shown that over the potential range 0.85 – 1.37 V platinum undergoes dissolution, the maximum corrosion rate being observed at E = 0.93 – 0.95 V. With time, the corrosion current decreases to 10^?6–10^?7 A/m². When platinum passes into solution the complex ion [Pt(OH)₆]^2? is formed. The influence of platinum pretreatment, leading to removal of surface oxygen compounds, on the rate of corrosion has been investigated. It has been found that Ba²⁺ ions slow down the dissolution process, while Cl^? ions increase its rate. The relationship between the platinum corrosion process and the shift of the oxygen electrode potential from the equilibrium value is discussed. Some conclusions are drawn about the mechanism of platinum corrosion.     

Effect of sodium sulfite on acid pretreatment of wheat straw with respect to its final conversion to ethanol

A pretreatment process that combines dilute acid and sodium sulfite has been applied to wheat straw to study the effect of temperature (120–180 °C) and sodium sulfite concentration (0–3%) on the yield of glucose in subsequent enzymatic hydrolysis and ethanol production by fermentation. The results were compared with both dilute acid pretreatment (without Na₂SO₃ addition) and hot water pretreatment. Formation of furfural and hydroxymethylfurural, which can inhibit ethanol-producing microorganisms, were measured and the ethanol yield in a subsequent fermentation was evaluated. The results indicate that a combination of 180 °C, 30 min, 1% H₂SO₄ and 2.4% Na₂SO₃ during pretreatment produced the highest ethanol yield; 17.3 g/100 g dry weight of initial biomass, which corresponds to 75% of the theoretical yield from glucose. 28 mg of furan inhibitors (sum of furfural and hydroxymethylfurfural) per gram dry weight of initial wheat straw were generated under this condition. Increasing sulfite loading up to 2.4% decreased inhibitor formation, leading to increased delignification and preservation of cellulose from dissolution. On the other hand, an elevated temperature in combination with low pH reduced the amount of solid phase after pretreatment, increased the level of inhibitors and reduced the concentration of ethanol produced by fermentation.     

Influence of mechanical and environmental variables on crack growth in PWR pressure vessel steels

Knowledge of the propagation rates of sub-critical cracks exposed to primary circuit coolant is essential for the use of defect assessment procedures for validation of PWR pressure vessel integrity. The results of research programmes conducted by the UKAEA to assess the conditions under which the PWR environment influences crack propagation of low alloy steels under cyclic and steady loading are described. The measured corrosion fatigue crack propagation rates for low and medium sulphur steels in good quality flowing water were well below those predicted by the ASME Section XI, Appendix A assessment curves, but higher rates were attainable for high sulphur steel or under adverse environmental conditions. No influence of material microstructure due to welding was observed in high flow water.No susceptibility to stress corrosion has been observed in bolt-loaded specimen tests on a range of parent steels and weldments. Cracking in slow strain rate tests was observed only at high potentials, such as were produced by the presence of dissolved oxygen, unless the specimen orientation was such as to maximise access of PWR coolant to sulphide inclusions in the steel.The implications of the data for operating plant and progress with the development of improved methods for assessing crack growth in operating plant are discussed.     

Propagation behaviour of general and localised corrosion of carbon steel in simulated groundwater under aerobic conditions

Abstract

Carbon steel is one of the candidate overpack materials for geological disposal of high-level radioactive waste in Japan. Corrosion of carbon steel is classified into two types: general corrosion and localised corrosion. In this study, propagation of general and localised corrosion (pitting corrosion and crevice corrosion) were investigated by immersion tests of carbon steel under the aerobic conditions. The results of the immersion tests showed that the corrosion growth rate was strongly dependent on the environmental conditions and type of steel. However, the upper limit of the pitting factor, the ratio between the maximum corrosion depth and the average corrosion depth, was determined approximately using only average corrosion depth. Based on the experimental and literature data, an empirical model that predicts the maximum corrosion depth of an overpack from average corrosion depth was developed by applying the extreme value statistical analysis using the Gumbel distribution function.