Atmospheric corrosion sulfur-containing compounds

One of the most important factors affecting atmospheric corrosion is the presence of specific pollutants. In areas having low atmospheric pollution, corrosion rates are correspondingly low. The presence of atmospheric pollutants such as the various oxides of nitrogen, sulfur-containing compounds, chlorine-containing compounds, and other less common pollutants will stimulate corrosion. 

Based on experience with atmospheric corrosion. Table 3.3 indicates that hard acids like and Ti form oxygen-containing films whereas soft acids such as Cu and Ag coordinate with reduced sulfur compounds. Intermediate acids such as Fe, Cu, and Zn would be expected to coordinate with a broader range of bases. 

It is obvious that atmospheric oxygen alone is not corrosive at normal climate temperatures. An aqueous electrolyte on the metal surface is essential for atmospheric corrosion. Depending on the climate the atmosphere contains a varying amount of water vapor (depending on the relative humidity). The corrosion severity is increased when salt, sulfur compounds and other contaminants are present. 

Many industrial atmospheres contain contaminants such as silicones, organic lead, sulfur compounds, and halogens which can poison catalytic sensors. Manufacturers go to great lengths in the design of these units to minimize loss of sensor activity from such influences.1 Means taken to keep water, corrosive liquids, and dirt from entering sensors involve the installation of membranes before the flame arrestor in front of the detector filament.2... 

The sulfur content of petroleum is an important property and varies widely within the rough limits 0.1% w/w to 3.0% w/w, and a sulfur content up to 8.0% w/w has been noted for tar sand bitumen. Compounds containing this element are among the most undesirable constituents of petroleum because they can give rise to plant corrosion and atmospheric pollution. Petroleum can evolve hydrogen sulfide during distillation as well as low-boUing sulfur compounds. 

Carbon monoxide is a colorless, odorless, flammable toxic gas. Liquid carbon monoxide is a cryogenic liquid, which exists at a temperature of -313°F (-192°C) and atmospheric pressure. It becomes a flammable vapor upon addition of heat. If inhaled, concentrations of 0.4 percent in air prove fatal in less than 1 hour, while inhalation of high concentrations can cause sudden collapse with little or no warning. Pure carbon monoxide has a negligible corrosive effect on metals at atmospheric pressures. Impure carbon monoxide, containing water vapor, sulfur compounds, or other impurities causes stress corrosion to ferrous metals at elevated pressures. 

In many cases, microbially influenced corrosion can be reduced or even completely prevented by adopting adequate constructive measures. This is exemplified below for a sewage pipeline system. If the atmosphere above the sewage contains a large quantity of volatile sulfur compounds like H2S, then if concrete pipes must be used, they should be protected with an inert material that cannot be attacked by the microbially formed... 

Industrial environments contain sulfur compounds, nitrogen compounds, and other acidic agents that can promote the corrosion of steels. In addition, industrial environments contain a heavier loading of airborne particles, which also contribute to corrosion. Urban environments are comparable with industrial, but the amount of pollution will be less intense. Marine environments are characterized by the presence of chloride, an ion that is particularly detrimental to the corrosion resistance of steels. Rural and indoor environments are the least corrosive of the atmospheric environments. 

Corrosion can proceed in a dry environment without any moisture if traces of sulfur compounds or H2S or other pollutants are present in the air. Tarnishing of silver in dry air in the presence of H2S traces is an example of dry corrosion. Industrial atmospheres contain SO2 as the major contaminant. 

Sulfur dioxide stimulates oxidation. It is the major driving force for corrosion in metropolitan areas. Most of the sulfur acquired by surface is not in the form of gas but as dry deposition. In an urban atmosphere, SO is abundantly found in aerosol particles. Large particles containing ammonia are also found. H2S, SO2 and COS in all these participate directly in the corrosion process. The sulfur compound, COS, hydrolyzes to form H2S and it may form CU2S if the quantity of COS is abundant on the other hand, SO2 may hydrolyze to form a bisulfate ion. 

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