What Does Industrial Atmosphere Mean?
An industrial atmosphere is an atmosphere in an area of heavy industry with soot, fly ash and sulfur compounds as the principal constituents.
Industrial atmospheres are generally the most aggressive in terms of corrosion. Air emissions may contain some sulfides and phosphates that cause coating consumption. Automobile, truck and plant exhaust are examples of these emissions. Most city or urban areas are classified as moderately industrial.
Corrosionpedia Explains Industrial Atmosphere
An industrial atmosphere is characterized by pollution composed mainly of sulfur compounds such as sulfur dioxide (SO2) and nitrogen oxides (NOx). Sulfur dioxide from burning coal or other fossil fuels is picked up by moisture on dust particles as sulfurous acid. This is oxidized by a catalytic process on the dust particles to sulfuric acid, which settles in microscopic droplets and falls as acid rain on exposed surfaces. It has been identified as one of the most important air pollutants which contributes to the corrosion of metals. Contaminants in an industrial atmosphere, plus dew or fog, produce a highly corrosive, wet, acid film on exposed surfaces.
Other corrosive pollutants may be present in or near chemical plants. These are usually various forms of chloride, which may be much more corrosive than the acid sulfates. The reactivity of acid chlorides with most metals is more pronounced than that of other pollutants such as phosphates and nitrates.
Less recognized as corrosion promoters, are the nitrogen oxides (NOx), which are also products of combustion. A major source of NOx in industrial atmosphere is the exhaust fumes from vehicles. Sulfur dioxide, NOx and airborne aerosol particles can react with moisture and UV light to form new chemicals that can be transported as aerosols. A good example of this is the summertime haze over many large cities. Up to 50% of this haze is a combination of sulfuric and nitric acids.
Carbon content in steel also has an impact of corrosion in industrial atmosphere. For example, structural carbon steel showed a penetration of about 20 µm, a copper structural steel about 10 µm, and low-alloy steel about 4 µm after five years of exposure.