Atmospheric corrosion

In the outdoor environment there are a variety of negative aspects of environment - air pollution, rainfall, humidity, sun radiation, etc., which act upon products, machinery, equipment, constructions, etc. As a result metal materials are attacked by corrosion and paint or metal coatings are being degraded. The corrosion process under atmospheric conditions is influenced by a variety of factors. In most cases electrochemical reactions are involved in atmospheric corrosion processes - anode and cathode reactions. The basic condition for the formation and course of atmospheric corrosion is therefore the formation of a moisture layer by the condensation of air moisture. The time of surface exposure to moisture is dependant upon many factors - temperature, relative air moisture, the type and amount of rainfall, wind speed, intensity of sun radiation, surface shape, its roughness and cleanness, degree of surface covering, etc. The rate of corrosion is strongly influenced by the concentration of pollutants in the atmosphere - most importantly SO₂ and chlorides. The rate of corrosion attack can be estimated from the data of atmospheric-aggressive action. For the estimation of corrosion attack on material the following is estimated:

• mass losses of a metal by an uniform corrosion over a period of time
• the danger of occurrence of an non-uniform corrosive attack and its type
• development of corrosion products on the surface and its character
• possibility of surface treatment of material to decrease corrosion failure