What Is Atmospheric Corrosion?

From a global perspective, the main composition of the atmosphere remains basically unchanged. According to experimental measurements, the composition of air by volume is approximately: 78% nitrogen, 21% oxygen, 0.94% rare gases, 0.03% carbon dioxide, and 0.03% other gases and impurities [ 4]. Due to natural location, climate and other conditions as well as man-made environmental pollution, the composition of the atmosphere has become complex and diverse, and some harmful components have a tendency to gradually increase. In particular, the global acid rain caused by sulfur dioxide and nitrogen dioxide in the air has aggravated the corrosion of steel materials, although there are no naturally occurring sulfur dioxide and nitrogen dioxide. However, the vast majority of these basic air pollutants are produced by human activities. Once the sulfur dioxide and nitrogen dioxide pollution gases emitted by humans enter the atmosphere, they may be converted into secondary pollutants nitric acid and sulfuric acid. These pollutants are easily soluble in water and form acidic water droplets that return to the ground to form acid rain, acid snow, etc.
Different types of impurities in the atmosphere have different effects on the corrosion rate of steel. Sulfur dioxide in the industrial atmosphere and salt particles in the marine atmosphere have the greatest impact on the corrosion rate of steel. In a pure rural atmosphere, the corrosion rate of steel is very low. Atmospheric corrosion of steel is a complex system. In addition to man-made environmental pollution, the corrosion rate is also related to wind speed and direction, temperature and rainfall, dew period, solar radiation, seasonal changes and even natural dust in the atmosphere. Even under the same external conditions, the corrosion rate on the back side of the steel due to rainwater deposition is significantly higher than that on the sunny side.