Structures atmospheric corrosion

Kucera, V. and Mattson, E., Atmospheric Corrosion of Bimetallic Structures, ex Atmospheric Corrosion, 561, J. Wiley and Sons, (1982)... 

In principle, cathodic protection can be used for a variety of applications where a metal is immersed in an aqueous solution of an electrolyte, which can range from relatively pure water to soils and to dilute solutions of acids. Whether the method is applicable will depend on many factors and, in particular, economics — protection of steel immersed in a highly acid solution is theoretically feasible but too costly to be practicable. It should be emphasised that as the method is electrochemical both the structure to be protected and the anode used for protection must be in both metallic and electrolytic contact. Cathodic protection cannot therefore be applied for controlling atmospheric corrosion, since it is not feasible to immerse an anode in a thin condensed film of moisture or in droplets of rain water. 

A wide range of paints and other organic coatings is used for the protection of mild steel structures. Paints are used mainly for protection from atmospheric corrosion. Special chemically resistant paints have been developed for use on chemical process equipment. Chlorinated rubber paints and epoxy-based paints are used. In the application of paints and other coatings, good surface preparation is essential to ensure good adhesion of the paint film or coating. 

The influence of mainly SO on the corrosion rate of several materials has been shown in numerous national exposure programs. During the last decades a number of empirical relations have been derived from measurements of atmospheric corrosion rates of the most important structural metals and from measurements of environmental factors. The results are usually presented in form of equations including pollution and meteorological parameters (5.). 

The accumulation of salts within the concrete pore structure can also lead to the corrosion of reinforcing steel, the fourth form of deterioration identified above. This corrosion is accompanied by an increase in the volume of the steel, which eventually causes the concrete to crack and spall. In discussing the atmospheric corrosion of concrete reinforcements, Skoulikidis (21) notes "The increase of atmospheric pollution Intensifies the corrosion tendency of the reinforcements in the atmosphere. The cracking of the concrete was observed more frequently with an increase of the atmospheric pollution (SO2, CO2, NH3, NOx> etc.) and the acceleration of the corrosion by the formation of a more conductive environment, that also chemically attacks the metals."... 

ASTMA32S Type 3 See Note 3 High-strength structural bolts Atmospheric corrosion resisting steel, quenched and tempered... 

External corrosion problems in oil and gas production normally are similar to those found in the pipeline industry, but as the lines are shorter and smaller in diameter, their economic impact on the total cost of production is limited. Atmospheric corrosion of structures and vessels is a problem for offshore fields and those operating near marine environments. 

The most important methods for preventing atmospheric corrosion are 1) to select a corrosion-resistant structural material, 2) to use a corrosion-resistant coating (metallic, inorganic, organic or composite), and 3) to close internal cavities in order to avoid access of humid air, or conversely, 4) to make sure that there is ample ventilation and drainage, and possibly 5) to supply oil, grease, or special substances such as tectyle to the cavities. 

In the realization of a structure or of a plant, we can make use of different metallic materials that, although not in contact and therefore not in galvanic coupling, must cross each other or, in any case, be positioned one above the other. In the case in which the products of the atmospheric corrosion of a material may constitute cathodic reagents for the dissolution of a material onto which they can leach out, the relative positions of the materials (i.e., above or below) are not equivalent from the corrosion point of view this is the case, for example, for the products of the atmospheric corrosion of copper, which can act as a cathodic reagent for the dissolution of iron and especially of zinc. It is therefore preferable that zinc and iron components are located above the copper ones. 

In the case, that pipes cross other metallic components, even if they are made of the same material, the choice about which one must be located above the other can be influenced by considerations about the possible damage caused on the underlying material, not only by the percolation of atmospheric corrosion products but also by the accidental spillage of liquids for example, it is preferable that electrical cables and gas pipes pass over and not under the sewage. In case of fire, stainless-steel structures can be anbrittled from contact with molten zinc it is therefore appropriate that the... 

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