钢芯铝绞导线大气腐蚀产物层的结构及腐蚀机理

在模拟大气腐蚀环境中,采用干/湿NaHSO3+NaCl水溶液盐雾试验研究钢芯铝绞(ACSR)导线腐蚀产物的相组成及腐蚀层结构,讨论其腐蚀机理。结果表明:ACSR导线中单股铝线或镀锌钢芯线的腐蚀主要表现为点蚀,腐蚀产物组成复杂,主要为锌和铝的氢氧化物、硫酸盐与氯化物的复式盐;在腐蚀初期,内外层铝股线及钢芯线表面镀锌层开始形成点蚀坑,逐步形成连续的腐蚀层;由于镀锌层和内层铝股线之间构成原电池,因为牺牲阳极效应,镀锌层腐蚀速率最大;而内层铝股线受到保护,腐蚀速率最小,外层铝股线腐蚀速率居中。     

Enhanced predictive corrosion modeling with implicit corrosion products

An advanced mathematical approach to describe the influence of corrosion products on the corrosion rate is presented here. The related model can be used as input equation for numerical predictive corrosion simulations or simply as an empirical model, to extrapolate experimental data of corrosion tests to longer times and to interpret the physical parameters behind. This semiempirical model assumes that a constant share of the dissolved metal precipitates on the surface and hinders the diffusion processes. Hence, the effective corrosion rate decreases exponentially with increasing dissolution. The explicit corrosion progress over time is derived by time integration on a newly developed, time dependent corrosion rate equation. The derived expression can be effortlessly implemented in existing for example finite element method, which is demonstrated for the uniform corrosion of a zinc surface. Furthermore, this approach is qualitatively compared with other empirical models for corrosion products and the validity is demonstrated by fitting of experimental data. A very good agreement between experiment and theory can be achieved for various materials and environments considering no change of the driving corrosion mechanism.     

Marine corrosion

Abstract

The accelerating effect of nitrates on the dissolution of tin sometimes observed in tinplate cans of acid products has been investigated by measurements of cathodic polarisation and by direct measurements of corrosion rate in oxygen-free solutions of sulphates and organic acids. The rate of reduction of nitrate, and hence the corrosion rate, increased as the corrosion potential of tin became more positive, possibly as a result of potential dependence of nitrate adsorption on tin. This finding may explain the known influences of pH, of dissolved tin and of the nature of the organic acids present, on the stimulation of corrosion produced by nitrate. The addition of anionic surface active agents created a negative shift of potential and inhibited corrosion but cationic agents caused a positive shift and stimulated corrosion. Sodium lauryl sulphate had a strong inhibitive effect at a concentration of 5 ppm and at 30 ppm almost completely suppressed the effect of nitrate.     

Adsorption characteristics of corrosion inhibitors from corrosion rate measurements

Corrosion rate data have been used for the determination of the adsorption parameters of the Frumkin isotherm in the system steel/acid solution/inhibitor. The inhibitors are derivatives of benzimidazole. The maximal amount of adsorbed inhibitor, the interaction parameter a and the equilibrium constant B of the isotherm are found simultaneously by using the SOLVER option of Excel. The statistical analysis of the results shows that this isotherm describes well the adsorption behaviour in the systems studied.     

AC corrosion. Part 2: Parameters influencing corrosion rate

Pipelines and AC power transmission lines frequently share corridors leading to AC interference corrosion problems, as documented by pipeline failures that have occurred in the USA, Canada and Europe, even when cathodic protection is applied. In order to investigate these phenomena, weight loss tests on carbon steel samples were performed in soil-simulating conditions (aerated and de-aerated sulphate solutions) at various AC current densities from 10 to about 900 A/m². Tests on freely corroding samples showed that the corrosion rate increased as AC current density increased; the effect of AC on corrosion rate was also detected at current densities lower than 30 A/m². The results obtained are analyzed and discussed together with polarization test results, which were presented in a previous paper by Goidanich et al. (submitted for publication) [1].     

The prediction of corrosion by statistical analysis of corrosion profiles

The corrosion of carbon manganese steel in CO₂-acidified sea water has been assessed by a statistical analysis of corrosion profiles. The total population of depth data was multi-modal and could not be fitted to any well known statistical models. However the deepest pits in the profile followed a type I extreme value distribution. The time dependence of the extreme value distribution parameters has been determined and used to predict the rate of penetration of steel components under pitting conditions.     

Monitoring corrosion rates and localised corrosion in low conductivity water

Monitoring of low corrosion rates and localised corrosion in a media with low conductivity is a challenge. In municipal district heating, quality control may be improved by implementing on-line corrosion monitoring if a suitable technique can be identified to measure both uniform and localised corrosion. Electrochemical techniques (LPR, EIS, crevice corrosion current) as well as direct measurement techniques (high-sensitive electrical resistance, weight loss) have been applied in operating plants. Changes in the corrosion processes are best monitored in non-aggressive, low conductivity media with sensitive electrical resistance technique and crevice corrosion current measurements.     

Forthcoming corrosion events

Abstract

The XX International Materials Research Congress (IMRC) 2011 was held during August in the tropical paradise of Cancun, in the Yucatan peninsula, Mexico. This is a joint event sponsored by the Sociedad Mexicana de Materiales (MRS-Mexico) and the Materials Research Society (MRS-USA).     

Forthcoming corrosion events

Abstract

Pitting potentials have been measured and some gravimetric testing has been carried out on a series of experimental austenitic stainless steels with varying chromium, molybdenum and nitrogen contents. All three of these elements were found to contribute to the resistance to the initiation of pitting corrosion, and synergistic effects have been noted. The effect of nitrogen is especially potent in a steel with 22% chromium and 3% molybdenum.     

Industrial corrosion monitoring

The paper describes the experience accumulated on electrochemical methods for corrosion monitoring. Electrical resistance, linear polarization, electrochemical potential and amperometric measurements are described and their reliability is evaluated together with that of the related commercial equipments. The main drawbacks of each method (e.g. sensibility, linear or non linear response, causes of error and correction…) are discussed.     

Co-operative corrosion phenomena

The corrosion of aluminium alloy 2024-T3 (AA2024-T3) was studied as a function of immersion time from 2.5 to 120 min in 0.1 M aqueous NaCl solution. At immersion times as short as 5 min, rings of corrosion product of 100 to 200 μm diameter, containing smaller domes of corrosion product, were observed using SEM. The domes of corrosion product had greater chloride concentrations than elsewhere on the surface and represented sites of anodic attack. As the immersion time was increased, significant grain boundary attack was observed within the rings of corrosion product. Analyses of Particle Induced X-ray Emission (PIXE) maps of the corroded surfaces showed a significantly higher number of IM particles around the chloride attack sites than the average particle density for the maps, indicating clustering of IM particles. These results suggest a co-operative corrosion effect as a result of clustering of the IM particles. A mechanism for the generation of the corrosion rings is discussed.     

A new perspective on measuring the corrosion rate of localized corrosion

Many corrosion phenomena are nonuniform, which means that anodic and cathodic locations are spatially separated. An example is macrocell corrosion of steel in concrete. Under these conditions, determining the corrosion rate from polarization resistance measurements and using the Stern–Geary equation is fundamentally not possible. We present a novel theoretical approach for the interpretation of galvanostatic pulse measurements, to make them applicable as a method for corrosion rate measurements in situations of localized corrosion. Experiments show that it is important to consider that (a) only a fraction of the applied current flows through the anode of the macrocell, and (b) this current is not constant over time. We propose an approach to quantify and consider these two effects, based on information generally accessible in condition assessment of concrete structures. Our results show that galvanostatic pulse measurements are a robust method to determine the corrosion current. With the traditional empirical approach, the measurement error was generally below factor 3, and occasionally up to factor 10. With the novel approach, this error could be reduced to a factor of maximum 2 in all cases.     

Study on corrosion of steels in marine environment by corrosion simulation device

Three kinds of steels were studied using electrically connected hanging specimen in the corrosion simulation device and offshore long scale hanging specimen. The experimental results obtained by the two methods show that the device can better reflect the offshore corrosion environment. A Ni‐Cu‐P steel specimen was studied through analysis of the specimen's corrosion products and corrosion types. The surface of the samples before and after the removal of the rust layer produced by these two methods were observed and compared after some experiments. The microstructure of the corrosion products under different marine environments were analyzed and compared through IR. It indicated good correlation between the electrically connected hanging specimen method and the long scale hanging specimen method.