Atmospheric corrosion description

The parameters that determine time of wetness and composition of surface electrolyte have been surveyed by Kucera and Mattson [8.1]. They present also a thorough description of the mechanism, with thermodynamic and kinetic aspects of corrosion on various materials. For instance, they consider potential-pH diagrams as a useful thermodynamic basis for understanding atmospheric corrosion. 

The following sections contain a brief description of the atmospheric corrosion performance of some metallic materials commonly used in atmospheric conditions. 

Of utmost importance in atmospheric corrosion is the presence of particles and aerosols (an ensemble of particles suspended in the air) of mostly chlorides, sulfates, and nitrates. The size, shape, and chemical and physical properties of these particles and aerosols can vary widely. A more detailed description of particles and their role in (indoor) atmospheric corrosion is given elsewhere [20]. 

The prevailing opinion was that stress corrosion should occur in atmospheric storage tanks [1278]. Therefore, it was somewhat surprising when cases of stress corrosion in atmospheric ammonia tanks were reported [1279]-[1281], Descriptions of further incidents, inspection techniques, and repair procedures can be found in [1276], [1282]-[1289], [1290],... 

Abstract Quality control of corrosion test results implies the validation of the corrosion test method and estimation of the uncertainty of corrosion rate measurement. The corrosion test in an artificial atmosphere of the salt spray mist needs evaluation of corrosivity of the test cabinet by reference specimens. Such calibration of corrosion environment raises very strict requirements for the method description and details of all procedures and used specimens. Reliable corrosion measurements by spray tests require validation of the experimental device together with the experimental procedure and determination of corrosivity uncertainty of the test cabinet environment. 

Several reviewers have given typical corrosion rates for these atmospheres (Table 2.1). Vazquez and Damborenea (1991) in particular point out the subjective nature of these descriptions and the different associated numerical values of corrosion rates such materials are used in this book because often that is the only description initially available for a location. In general terms, Scandinavia and the Iberian peninsula have purer air than central and northwestern Europe North America aligns more with the less polluted parts of Europe. This distribution is reflected in the use of the subjective terms thus corrosion in an industrial atmosphere in Finland may be little worse than in some rural atmospheres in England. 

Because corrosion occurs differently in different parts of the world, qualitative descriptions of atmospheres as urban, industrial, marine, or rural are of significance only within a specific geographic region, and multiplication factors need to be determined for any other region. Nevertheless, it can be helpful to show the range of zinc corrosion rates in this form (Tables 2.3-2.6). SO2 content and time of wetness should be obtained wherever possible (see Tables 2.7A and B). 

Section V on Testing in Environments (H. Hack, Section Editor) includes chapters on outdoor and indoor atmospheres, seawater, fresh water, soils, concrete, industrial waters, industrial chemical, petroleum, high-temperature gases, organic liquids, molten salts, liquid metals, corrosion inhibitors, in-vivo, and microbiological effects. Each chapter provides a descriptive overview of the environment and factors and variables affecting corrosion rates and mechanisms. 

General Description. Uniform or general corrosion, as the name implies, results in a fairly uniform penetration (or thinning) over the entire exposed metal surface. The general attack results from local corrosion-cell action that is, multiple anodes and cathodes are operating on the metal surface at any given time. The location of the anodic and cathodic areas continues to move about on the surface, resulting in uniform corrosion. Uniform corrosion often results from atmospheric exposure (especially polluted industrial environments) exposure in fresh, brackish, and salt waters or exposure in soils and chemicals. 

Description and corrosion resistance. Alloy 800 is a nickel-iron-chromium alloy with good strength and excellent resistance to oxidation and carburization in high-temperature atmospheres. It also resists corrosion by many aqueous environments. 

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