J. Simancas

Corrosion of Rusted Steel in Aqueous Solutions of Tannic Acid

Abstract The use of tannic acid to inhibit metal corrosion has been a controversial issue, particularly in relation to its application to rusted steel prior to painting. In this work, the protectiv...

Long-term atmospheric corrosion in Spain: results after 13-16 years of exposure and comparison with worldwide data

Available information on atmospheric corrosion over long periods of time (10-20 years or longer) is unfortunately very scanty despite its great usefulness; in fact, only from such type of data can reliable long-term atmospheric corrosion predictions be made. This paper reports the results obtained after 13-16 years of field exposure tests at various Spanish test sites including several types of atmosphere: rural (E1 Escorial), urban (Madrid, Zaragoza), industrial (Bilbao), and marine (Barcelona, Cadiz, Cabo Negro, Alicante). Panels of low-carbon steel, zinc, copper, and aluminum were removed from open-air racks after 1-6, 8, 10, 13, and 16 years of exposure, and their weight losses used to determine the corrosion rate. Long-term corrosion data were found to conform to a general equation, C = At n , where A and C are the corrosion losses after one and t years of exposure, respectively, and n is a constant. Only mild steel in scarcely aggressive atmospheres of central Spain was found to fit a more complex equation. The results are compared with those found throughout the world, which were compiled in a comprehensive literature survey. Finally, an attempt was made at correlating exponent n with the type of atmosphere for each metal studied.

Effect of variable amounts of rust at the steel/paint interface on the behaviour of anticorrosive paint systems

This paper analyses the effect of the presence of rust at the metal/paint interface on the behaviour of different paint systems used for protecting the structural steel exposed to the atmosphere. The paint systems were applied as films of variable thickness over rusted steel surfaces cleaned to different grades of surface preparation (Sa3, Sa2(1/2), Sa2 and St2). Pre-rusting of steel was carried out in a clean (uncontaminated) rural atmosphere. Atmospheric exposure tests were conducted for 14 years at three Spanish test sites of different atmospheric corrosivity. Exposed specimens were evaluated for rusting and blistering, as well as for delamination of the paint system on both sides of a scribe made in the paint film. The results reveal that in some cases the presence of rust has a negligible influence on the durability of the paint system applied. Those systems including a zinc-rich (ethyl silicate) primer were found to provide the most effective protection against corrosion under all types of conditions tested.

Rust exfoliation on carbon steels in chloride-rich atmospheres

Abstract The exposure of carbon steel in marine atmospheres can lead in certain circumstances to the formation of thick rust layers (containing a number of compact laminas) that are easily detached (exfoliated) from the steel substrate, leaving it unprotected and considerably accelerating the corrosion process. This deterioration phenomenon is of particular concern in steel infrastructures located close to the sea (civil constructions, bridges, etc.), whose service lifetime can be extraordinarily limited. High times of wetness of the metallic surface and high chloride ion deposition rates play a decisive role in the formation of this type of rust. Research has been carried out for 1 year in eight pure marine atmospheres with annual average chloride deposition rates of 70–1906 mg Cl-/m2 day. The studied carbon steels consisted of one mild steel, one conventional weathering steel (Corten A), and one high nickel (~3 wt.%) advanced weathering steel (AWS). The paper describes the environmental conditions that lead to the formation of these thick multilaminar rust layers and presents a characterisation study of this singular type of rust using a variety of analysis techniques: scanning electron microscopy/energy-dispersive X-ray spectroscopy, X-ray diffraction, Mössbauer spectroscopy, and transmission electron microscopy/electron diffraction. The Ni-AWS shows greater resistance to the occurrence of rust exfoliation.

Looking Back on Contributions in the Field of Atmospheric Corrosion Offered by the MICAT Ibero-American Testing Network

The Ibero-American Map of Atmospheric Corrosiveness (MICAT) project was set up in 1988 sponsored by the International Ibero-American programme “Science and Technology for Development (CYTED)” and ended in 1994 after six years of activities. Fourteen countries were involved in this project: Argentina, Brazil, Chile, Colombia, Costa Rica, Cuba, Ecuador, Mexico, Panama, Peru, Portugal, Spain, Uruguay, and Venezuela. Research was conducted both at laboratories and in a network of 75 atmospheric exposure test sites throughout the Ibero-American region, thus considering a broad spectrum of climatological and pollution conditions. Although with its own peculiarities, the project basically followed the outline of the ISOCORRAG and ICP/UNECE projects, with the aim of a desirable link between the three projects. This paper summarizes the results obtained in the MICAT project for mild steel, zinc, copper, and aluminum specimens exposed for one year in different rural, urban, and marine atmospheres in the Ibero-American region. Complementary morphological and chemical studies were carried out using scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and fourier transform infrared Spectroscopy (FTIR) techniques, in order to correlate climatic and atmospheric conditions and properties of the corrosion products.

X-Ray Photoelectron Spectroscopy Study of the Effect of Nitrogen Dioxide and Sulfur Dioxide on the Atmospheric Corrosion of Copper at Low Relative Humidity Values

Abstract A study has been made of the individual and combined roles of nitrogen dioxide (NO2) and sulfur dioxide (SO2) atmospheric pollutants on corrosion and patina formation on copper in atmospheres with comparatively low water contents (70% and 50% relative humidity [RH]) for exposure times of up to 28 days. X-ray photoelectron spectroscopy (XPS) analysis has revealed some important compositional changes in the outermost atomic layers of films formed on copper, depending on the nature of the atmospheric pollutant, the humidity level, and the exposure time. After 7 days of exposure to NO2, a significant nitrogen content is detected (mainly as nitrates). In contrast, in exposure to SO2, copper oxides are present on the patina surface even after 21 days of exposure. In exposures to the mixture of NO2 + SO2, a nitrate layer grows on a copper sulfate film. As with NO2 alone, the appearance of nitrates leads to an appreciable increase in mass gain values.

Marine Atmospheric Corrosion of Carbon Steel: A Review

The atmospheric corrosion of carbon steel is an extensive topic that has been studied over the years by many researchers. However, until relatively recently, surprisingly little attention has been paid to the action of marine chlorides. Corrosion in coastal regions is a particularly relevant issue due the latter’s great importance to human society. About half of the world’s population lives in coastal regions and the industrialisation of developing countries tends to concentrate production plants close to the sea. Until the start of the 21st century, research on the basic mechanisms of rust formation in Cl−-rich atmospheres was limited to just a small number of studies. However, in recent years, scientific understanding of marine atmospheric corrosion has advanced greatly, and in the authors’ opinion a sufficient body of knowledge has been built up in published scientific papers to warrant an up-to-date review of the current state-of-the-art and to assess what issues still need to be addressed. That is the purpose of the present review. After a preliminary section devoted to basic concepts on atmospheric corrosion, the marine atmosphere, and experimentation on marine atmospheric corrosion, the paper addresses key aspects such as the most significant corrosion products, the characteristics of the rust layers formed, and the mechanisms of steel corrosion in marine atmospheres. Special attention is then paid to important matters such as coastal-industrial atmospheres and long-term behaviour of carbon steel exposed to marine atmospheres. The work ends with a section dedicated to issues pending, noting a series of questions in relation with which greater research efforts would seem to be necessary.

Differences between apparent polarization resistance values obtained in the time and frequency domains

Abstract Anomalously large differences between values of the polarization resistance R p measured in the time and frequency domains pose a serious problem in determination of the corrosion rate from the Stern-Geary equation. A theoretical model is used to derive expressions for a quantitative interpretation of the effect of a number of parameters on the apparent R p values obtained by dc and ac measurements. Problems associated with the determination of the true R p value are discussed, and some relevant questions concerning the minimum frequency needed for impedance measurements are identified.

Electrochemical determination of rusted steel surface stability

The stability of a rusted steel surface exposed to a 0.11 M sodium sulphate solution has been studied. Electrochemical impedance spectroscopy, polarization resistance and atomic absorption analysis techniques were used in conjunction with mild steel specimens rusted in a rural atmosphere and treated with different concentrations of phosphoric acid. Since most of the impedance diagrams obtained differ from the typical semicircle, it is not clear how to obtain kinetic information on the corrosion process. The polarization resistance technique gives more useful data.

Accelerated degradation of a chlorinated rubber paint system applied over rusted steel

Abstract Chlorinated rubber coatings have proved to be effective anticorrosion materials for steel structures. However, their formulation and manufacture must be undertaken with extreme care — particularly as regards the chlorination process and the stabilizers and plasticizers added — in order to avoid early failures. This paper reports on the premature failure of a chlorinated rubber system that was applied directly over uncontaminated rusted steel. The accelerated formation of rust at the steel/paint interface rapidly resulted in complete degradation of the organic coating. Interfacial rust appears to catalyze the cleavage of the C-Cl covalent bonds in the polymer, which gives rise to the formation of chloride ions. These in turn have a dramatic accelerating effect on the corrosion of the base steel, thereby deteriorating the paint system.