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An electrochemical macrocell between repaired and adjacent unrepaired zones has been reported when a local concrete patch is performed. This macrocell seems to lead to the corrosion of neighboring not repaired zones. Previous experiments of the authors in slightly chloride contaminated concrete have shown that the macrocell activity lasts very short time (only during the curing). In present paper the effect to rise the temperature to 40°C maintaining the RH, typical of tropical climates, is studied. The results show that the galvanic effect is not enhanced while the corrosion rate does it, which confirms the independence of the galvanic current from the corrosion rate. 相似文献
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Chemical process installations are exposed to aggressive chemicals and conditions leading to corrosion. The damage from corrosion can lead to an unexpected plant shutdown and to the exposure of people and the environment to chemicals. Due to changes within and on the surface of materials subjected to corrosion, energy is released in the form of acoustic waves. This acoustic activity can be captured and used for corrosion monitoring in chemical process installations. Wavelet packet coefficients extracted from the acoustic activity have been considered to determine whether corrosion occurs, and to identify the type of corrosion process, at least for the most important corrosion processes in the chemical process industry. Feature subset selection is then applied to these wavelet coefficients to achieve a much higher accuracy in the identification of different corrosion processes than when no feature subset selection is applied to the acoustic waves. However, due to the statistical dependencies that potentially exist between the wavelet coefficients, the latter should not be selected independently from each other. Local discriminant basis selection algorithms do not take the statistical dependencies between wavelet coefficients into account. In this paper, we have used several mutual information-based approaches that take these dependencies into account and compared them to the wavelet-specific local discriminant basis selection algorithm. Furthermore, a hybrid filter-wrapper genetic algorithm, which uses a relevance-redundancy approach as a local search procedure, was designed. The highest classification accuracies are obtained with the hybrid filter-wrapper genetic algorithm, for all classifiers used in this paper. Furthermore, the proposed algorithm easily outperformed one of the most commonly used classifiers in chemometrics: partial least squares discriminant analysis (PLS-DA). A naïve Bayes classifier that uses the features selected by the hybrid filter-wrapper genetic algorithm was able to identify the absence of corrosion, uniform corrosion, pitting and stress corrosion cracking, with an accuracy of up to 87.20%. 相似文献
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F. Simonsen J. Weber R. Rennert M. Oechsner 《Materialwissenschaft und Werkstofftechnik》2018,49(6):703-713
Zinc‐based corrosion protection systems provide the user with a favorable and long‐ lasting opportunity to protect steel components from corrosion. Therefore, these systems are used in many different variants and are state of the art. Investigations show that zinc‐based corrosion protection systems can have an influence on the fatigue strength during cyclic loading. This influence is not or only partly taken into account in current design regulations. In this paper, the influence on the fatigue strength and possibilities to consider the influence in the design against material fatigue is shown. 相似文献
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This paper presents experimental data for a 0.2%C steel/artificial seawater system showing the influence of shear loading on corrosion response, via measurements of electrochemical variables, e.g. anodic/cathodic Tafel slopes and polarization resistance. Based on the results of these tests, several corrosion fatigue tests were conducted at different stress levels under potentiostatic control. Analysis of the results shows there to be a dependence of corrosion rate on the ratio of applied/yield strain and test frequency. In addition, the corrosion current associated with corrosion fatigue (CF) damage appears to be dependent upon the crack size, which in turn shows a relationship with fatigue crack growth rate. This paper sets out to determine the influence of stress on electrochemical parameters, i.e. free corrosion potential, Ecorr , polarization resistance, Rp , anodic, τa and cathodic, τc Tafel constants. Based upon these results, it is found that a simple linear relationship between stress and corrosion damage does not exist. Furthermore, analysis of the corrosion current fluctuations during corrosion fatigue crack growth shows a minimum current coincident with the point at which a crack is growing at its slowest rate. 相似文献
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Anatolii Babutskyi Andreas Chrysanthou Marija Smelina Gennadii Stepanov Maciej Ziętara 《Materials Science & Technology》2017,33(12):1461-1472
ABSTRACTResults of corrosion tests of titanium in the initial state and after treatment using pulsed magnetic field are presented. It is shown that samples after treatment have better corrosion resistance due to the formation of denser and finer corrosion products with better adhesion to the substrate. Samples after treatment have more homogeneous microstructure due to a substantial increase of dislocations which are uniformly distributed. Mechanisms of dislocation multiplication and a model explaining the effect of the treatment on the corrosion are discussed.This paper is part of a themed issue on Materials in External Fields. 相似文献
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Polarisation resistance (Rp) technique based on Stern–Geary equation is one of the most widely used methods of measuring corrosion rate of reinforcement in the field. With the aid of a “sensorised guard ring”, this electrochemical technique is claimed to be able to determine corrosion rate (Icorr) within a given measuring area. However, there are three theoretical problems in the application of this technique: (1) the original Stern–Geary equation is applicable in a uniform corrosion system at its corrosion potential, whereas the reinforced concrete structure may be subjected to non-uniform corrosion or strong polarisation by macro-cell galvanic effects or imposed currents; (2) the value of the parameter B in the original Stern–Geary equation has been estimated to fall within the range 25–52 mV. This may not be suitable for all the corrosion cases of reinforced concrete structures; (3) The polarised surface area of steel may theoretically not always be fully confined by the sensorised guard ring when the cover concrete is too thick.
This paper aims at discussing the theoretical problems. A general relationship between the dissolution rate of steel reinforcement and the measured polarisation resistance is deduced under general conditions. The range of B value is also analysed based on all the possible corrosion situations of reinforced concrete. Furthermore, unsatisfactory confinement by sensorised guard ring on a thick cover concrete is demonstrated. 相似文献
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This paper will focus on the study of reinforced concrete beams stored in a chloride environment for a period of 14–23 years
under service loading. According to the experimental results, a Serviceability Limit State (SLS) criteria is proposed based
on an excessive steel–concrete bond reduction. Corrosion of reinforcement in chloride environment leads to a specific local
steel cross-section loss as well as a steel–concrete bond loss. Experimental results have shown that, in the first stage of
corrosion propagation period, the deflection is more sensitive to chloride-induced corrosion than the ultimate capacity due
to the effect of the tension steel–concrete bond loss even if both are correlated. Given this high sensibility of the bending
stiffness to corrosion pitting attacks, it appears that a Serviceability Limit State (SLS) criteria based on excessive deflection
of structural members is an adequate factor for SLS assessment. Later in corrosion propagation period, when the bond is already
significantly reduced, only the ultimate capacity is affected by the steel cross-section loss. This does not affect the serviceability,
because pitting attacks are very localised with an insignificant influence on the global deflection. Then, once the steel–concrete
bond is lost in critical parts of the beams (high bending moment areas), pitting corrosion propagation does not affect anymore
serviceability (stiffness reduction, bending or corrosion cracks patterns) but still leads to an ultimate capacity reduction,
which is not acceptable. As a result, excessive steel–concrete debonding can be considered as the SLS criteria. 相似文献
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Corrosion of steel in reinforced concrete structures is a recurrent problem affecting civil engineering structures and costing the world billions of dollars per year. This physical phenomenon mainly results from chloride ingress or concrete carbonation. Corrosion can be diagnosed through a nondestructive method such as half-cell potential measurements. The present paper studies this method on a reinforced concrete wall containing eighteen unconnected steel bars and subjected to chloride-induced macrocell corrosion. Three corrosion systems with different configurations of connections between the steel bars are generated, involving three different anode-to-cathode surface ratios. Then, half-cell potential variations are observed versus macrocell corrosion current. The results lead to a critical discussion regarding the physical relevance of the usual potential threshold method to detect corroding rebars in reinforced concrete structures. In addition, the experiments demonstrate that electrical continuity between reinforcing steel bars is not necessary to get meaningful information about the macrocell corrosion system. At last, the paper show that the electric field (potential gradient) relative to a macrocell corrosion system may be measured by connecting the measurement system (reference electrode?+?voltmeter) to any electrochemical system in electrolytic contact with the concrete. 相似文献
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文章对服役于某天然气井的20^#钢弯管进行了成分、组织、力学性能及腐蚀产物分析,并与未服役的20^#钢弯管进行了对比,评价研究了其抗H2S腐蚀的程度。研究结果表明:20^#钢弯管发生了H2S腐蚀,但并没有引起氢致损伤;H2S腐蚀后,腐蚀区域硬度降低,塑性下降。 相似文献
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This paper advocates for the adoption of performance-based limiting crack widths with respect to steel corrosion in reinforced concrete structures. The authors argue that, from both durability and sustainability viewpoints, the practice of adopting a universal limiting crack width for a wide range of in-service exposure conditions and concrete cover conditions and quality is not valid. As new performance-based concrete design codes are being developed and/or improved, the influence of cover cracking on steel corrosion needs to be incorporated in these codes. An experimental set-up was designed to investigate the influence of cover cracking, cover depth and concrete quality on chloride-induced corrosion. Beam specimens (120?×?130?×?375?mm) were cast using five concretes made using two w/b ratios (0.40 and 0.55) and three binders (100?% CEM I 42.5?N (PC), 50/50 PC/GGBS and 70/30 PC/FA). Other variables in the experiments included cover depth (20 and 40?mm), crack width (0, 0.4 and 0.7?mm). A total of 105 beam specimens were cast and exposed to cyclic 3-days wetting (with 5?% NaCl solution) and 4-days air-drying in the laboratory (23?°C, 50?% relative humidity). Corrosion rate was monitored bi-weekly in the specimens. The results relevant to this paper are presented and discussed. For a given concrete quality and cover depth, corrosion rate increased with increasing crack width. If crack width and cover depth are kept constant, corrosion rate increases with decreasing concrete quality, and vice versa. A model framework that can be used to objectively select cover depth, concrete quality and crack width is proposed. Such a model can be improved into, for example, a nomograph and used in the design process for RC structures prone to corrosion. Performance-based crack width limits should be adopted in the design of RC structures prone to steel corrosion. These crack width limits should be dependent on a complex interaction of, inter alia, concrete quality, cover depth, crack characteristics and prevailing exposure conditions. This study showed the inter-relationship between crack width, cover depth and concrete quality in affecting chloride-induced corrosion rate. Accurate corrosion rate prediction models incorporating the influence of cover cracking on corrosion are a pre-requisite to implementing the influence of cover cracking in future concrete design codes. 相似文献
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Koichi Kobayashi Takahiro Iizuka Hoshito Kurachi Keitetsu Rokugo 《Cement and Concrete Composites》2010,32(6):411-420
This paper regards the corrosion protection performance of High Performance Fiber Reinforced Cement Composites (HPFRCC) as a repair material. For the purpose of improving workability, the volumetric fiber content in HPFRCC was decreased from its usual rate of 1.5% to as low as 0.75%. The applicability of HPFRCC as a repair material for preventing steel corrosion was investigated using specimens that simulated either surface coating repair or patch repair. The results can be summarized as follows: Patch repair with HPFRCC to depths beyond the backside of the reinforcement effectively suppressed chloride penetration and prevented reinforcement corrosion, whereas surface coating with HPFRCC could not prevent corrosion of the steel in the RC substrate. As long as the fiber content is set so that only fine cracks are formed under service conditions, differences in fiber content did not affect the corrosion preventing performance of HPFRCC as a repair material. 相似文献
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管道运输以其经济成本低、安全性及自动化程度高等显著优势,被广泛应用于油气领域。管线钢是一类运输油气资源的特种钢材,表现出较为优异的服役性能。腐蚀作为影响材料的三大主要因素之一,会对管道材料产生巨大影响,进行管线钢腐蚀行为和机理研究极具意义。管线钢服役环境繁杂,既用于埋地管道铺设,也在海洋环境中具有较大发展潜力。影响管线钢耐蚀性能的因素主要包括材料自身性质、服役环境(土壤及海洋)、单一酸性气体、油气性质、缓蚀剂和外加载荷等。不同因素之间存在一定程度的协同与拮抗作用,相比于单因素作用,多因素之间的耦合效果会大幅改变管线钢的腐蚀情况。概述了管线钢最新腐蚀研究现状,阐述了单因素的单独作用和多因素之间的耦合作用,简要分析了管线钢在腐蚀研究方面所面临的困难,以及对未来研究的展望,以期为管线钢腐蚀防护提供一定的思路和解决措施。 相似文献
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This paper is aimed at investigating the corrosion behaviour, microstructure and phase transitions of Zn-based alloys with
different compositions. The corrosion tests are carried out both in acidic medium using 1 N HCl solution and in temperature
dependence of thermogravimetric analysis (TGA). In the two different media, in particular, the corrosion behaviour of Zn-based
alloys with respect to Al and Si contents is examined, and microstructure in acidic and TGA and phase transformations in TGA
are also studied. Corrosion mechanism in TGA is also examined in terms of oxidation parameters and activation energies. The
study reveals that corrosion behaviour of Zn-based alloys in acidic medium shows sometimes an increase and sometimes a decrease
with time due to Al content which assists in delaying the corrosion by forming a oxide layer on the surface of Zn-based alloys.
This property does not appear in temperature dependence of TGA. Further, Si content appears to remain in main matrix without
being affected by acidic solution. On the other hand, it is observed that in microstructure, AlO(Al2O3), ZnO oxides and Zn-Cu phase precipitations are formed in main matrix, grain boundaries and partially inside the grains. 相似文献
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对比研究了静态铝热SHS陶瓷涂层在不同组成,不同冷却保温条件和腐蚀阶段的耐蚀性,试验得出,腐蚀在第一阶段最为严重以后趋于平缓稳定,添加SiO2和保温缓冷的涂层可减少孔隙,改善组织分布,从而提高耐蚀性。 相似文献