Manuel Morcillo

The prediction of atmospheric corrosion from meteorological and pollution parameters—I. Annual corrosion

Abstract Worldwide atmospheric corrosion and environmental data, compiled in a comprehensive literature survey were statistically processed for establishing general corrosion damage functions for mild steel, zinc, copper and aluminium, in terms of simple meteorological and pollution parameters. The regression equations thus developed account for 83, 62, 59 and 41% of the variance in the annual corrosion data for zinc, steel, aluminium and copper, respectively. The goodness of the fits of data from rural atmospheres is considerably lower.

THE PREDICTION OF ATMOSPHERIC CORROSION FROM METEOROLOGICAL AND POLLUTION PARAMETERS--II. LONG-TERM FORECASTS

Abstract Long-term atmospheric corrosion forecasts often rely on the fulfilment of equations of the form C = At n , where C is the corrosion after t years and A represents corrosion after the first year of exposure. Appropriate values must be assigned to constants A and n . In the first part of the work an analysis was performed on the possibility of expressing A as a function of usually available environmental parameters. In this second part data compiled in a comprehensive literature survey are used to determine whether the exponent n of the above equation can also be expressed as a function of such environmental parameters.

The charge transfer reaction in Nyquist diagrams of painted steel

Abstract When applying the AC impedance technique to metal-paint systems, it is of interest to identify the corrosion reaction of the metallic substrate in the arcs appearing on the complex plane of the Nyquist diagrams. This article shows how difficult it sometimes is to obtain direct information on this reaction on the basis of the diagrams obtained. The use of peelable films has been demonstrated to be very useful for this research. With these films it is possible to separate the effect of the metallic substrate from that of the film in the impedance diagrams, first measuring with the film adhered to the metallic surface and then with the same film detached from the substrate.

The atmospheric corrosion mechanism of 55%Al-Zn coating on steel

This paper presents the results of a study aimed at understanding the atmospheric corrosion mechanism of the 55%Al-Zn coating (Galvalume) on steel and a comparison with the behaviour of galvanized sheets (Sendzimir). Research has been carried out in different types of atmosphere in Spain, Brazil and Portugal. Unlike the galvanized coating, which suffers a generalized attack of its surface, the 55%Al-Zn coating undergoes a localized type of attack which commences in the interdendritic regions of the material. An analysis is also made of the additional protection which may be provided by a chemical passivating treatment applied on both types of coating.

Effect of Distance from Sea on Atmospheric Corrosion Rate

Abstract The influence of the distance from sea constitutes one of the most important aspects of atmospheric corrosion in coastal areas. Empirically, it is known that the effect of marine atmospher...

Artificial neural network modeling of atmospheric corrosion in the MICAT project

This paper presents an Artificial Neural Network(ANN)-based solution methodology for modeling atmospheric corrosion processes from observed experimental values, and an ANN model developed using the cited methodology for the prediction of the corrosion rate of carbon steel in the context of the Iberoamerican Corrosion Map (MICAT) Project, which includes seventy-two test sites in fourteen countries throughout Iberoamerica. The ANN model exhibited superior performance in terms of goodness of fit (sum of square errors) and residual distributions when compared against a classical regression model also developed in the context of this study, and is expected to provide reasonable corrosion rates for a variety of climatological and pollution conditions. Furthermore, the proposed methodology holds promise to be an effective and efficient tool for the construction of analytical models associated with corrosion processes of other metals in the context of the MICAT project, and, in general, in the modeling of corrosion phenomena from experimental data.

Atmospheric corrosion of bare and anodized aluminium in a wide range of environmental conditions. Part I: Visual observations and gravimetric results

Abstract This study compares the behaviour of aluminium in the bare condition and when protected with anodic films of approximately 7, 17 and 28 μm thickness for 42 months of exposure in 11 atmospheres of very different aggressivities, with salinity values ranging from between 2.1 and 684 mg Cl − m −2 d −1 . The anodic films, obtained in a sulfuric acid bath and sealed for 60 min in boiling deionized water, were characterised before and after different exposure times by means of: visual inspection; observation with a magnifying glass; and using classic gravimetric techniques. Optical and electron microscopy were occasionally used with some specimens that showed symptoms of localised corrosion. Aluminium behaves as a passive material in atmospheres of low salinity but exhibits pitting corrosion after 1 year at chloride pollution levels of ≥50 mg Cl − m −2 d −1 and after 2 years at levels of ≥10 mg Cl − m −2 d −1 . Anodising and sealing prevents the risk of pitting corrosion even in the most aggressive atmospheres, except in the case of the coatings of the lowest thickness.

Soluble salts : their effect on premature degradation of anticorrosive paints

Abstract The presence of soluble salts (particularly sulphates and chlorides) at the metal/paint interface is known to have a detrimental effect on the integrity of most paint systems. Though this is a long-standing problem, it has recently come to receive greater attention from the protective coatings industry. International standards organization (ISO) has for some time been trying to develop a standard about guidance levels for water-soluble salt contamination before the application of paints and related products. In the paper the following points are reviewed: degradation mechanisms of the metal/paint system, the role of the metallic substrate, the nature, origin and detection of soluble salts, expected levels of soluble salts in practice, critical thresholds of soluble salts and risk levels for premature failures, role of the type and thickness of paint systems and exposure conditions, and prevention measures. The author presents an overview of the subject, making reference to the related research that has been carried out by him and his co-workers over the last 15 years.

Atmospheric corrosion of copper in Ibero-America

Abstract Within the framework of the American Map of Atmospheric Corrosiveness (MICAT) project, 4 years of field research on atmospheric corrosion carried out in 14 countries of Ibero-America, this paper reports atmospheric copper corrosion in 21 unpolluted rural atmospheres and 45 marine atmospheres covering a broad interval of climatic conditions. High temperatures and relative humidities seem to promote greater copper corrosion in rural atmospheres; attack rates are found in the range of 0.1 μm/y to 2 μm/y, and corrosion product layers, generally comprising only cuprite (Cu2O), are discontinuous and have open structures with patinas acquiring increasingly darker colors (from salmon pink to dull brown) with exposure time. From the results obtained at marine sites, a critical deposition rate threshold is inferred for atmospheric salinity (20 mgCl−/m2 per day), after which the atmospheric corrosion of this material is intensified.

A SEM study on the galvanic protection of zinc-rich paints

The research is focused directly to the cahodic protection mechanism of zinc-rich paints (ZRP). It is based on a systematic scanning electron microscope (SEM) observation of cross-sections of several ZRP coatings exposed for different time intervals to a 3% (by weight) sodium chloride solution. The effect of vehicle (binder) used in the paint formula and the effect of zinc particle content are considered.As the anodic behaviour of zinc particles depends very closely on coating microstructure, SEM observation of the latter is very useful to investigate the galvanic performance of ZRP. This study confirms that high zinc particle contents and the use of ethyl silicate as a vehicle favour the degree and duration of the cathodic protection.Depending upon whether the zinc particles act anodically or not their attack mechanism is radically different. Accordingly, two attack mechanisms of the zinc particles are proposed.