The long-term use of the air storage tank or after many years of use will inevitably cause rain, air or humid atmospheric corrosion, which is caused by the action of water, oxygen, acidic pollutants and other substances in the atmosphere. It is a common atmospheric corrosion phenomenon that steel rusts in the atmospheric natural environment

There are three types of atmospheric corrosion:

① Dry atmospheric corrosion. At this time, there is basically no water vapor in the atmosphere, and ordinary metals form invisible oxide films at room temperature. The surface of steel is kept glossy.

② Wet atmospheric corrosion. It refers to the corrosion of metal under the thin film layer invisible to the naked eye. At this time, there is water vapor in the atmosphere. When the water vapor concentration reaches the critical humidity (the critical humidity of iron is 65%, and the critical humidity of copper is close to 10 0%), there is a very thin water film on the metal surface, and uniform corrosion will occur. If there are pollutants such as CO2, H2S and SO2 in the atmosphere, the corrosion will be significantly accelerated. The corrosion of steel under atmospheric conditions is actually electrochemical corrosion under water film conditions.

③ It can be seen that the gas tank is corroded under the condition of liquid film. It refers to the corrosion caused by the relative humidity in the air of about 1 00% or in rain and other aqueous solutions. At this time, water forms droplets on the metal surface, and there is a water film visible to the naked eye.