What are the five types of corrosion environment for coating anticorrosion?

Atmospheric corrosion

Atmospheric corrosion is a process that occurs inside a wet film on the surface of steel structures. The wet film layer may be too thin to be visible to the naked eye.
The following factors will cause the corrosion rate to increase:

The rise in relative humidity;
Condensation occurs (when the surface temperature is at or below the dew point);
The total amount of air pollutants is rising (corrosive pollutants can react with steel and may form deposits on the surface).
Experience has shown that severe corrosion usually occurs when the relative humidity is greater than 80% and the temperature is higher than 0°C. However, if pollutants and hygroscopic salts are present, corrosion will also occur at lower humidity. The atmospheric humidity and air temperature in a particular area on the earth depend on the local climatic conditions. The location of the various components of the steel structure also affects corrosion. Therefore, the steel structure exposed to the open air will corrode under the influence of climatic parameters such as rain, sunlight, gas or suspended pollutants. The influence of indoor air pollutants is reduced, and there may also be local high corrosion due to insufficient ventilation, high humidity or condensation. For the judgment and evaluation of corrosion stress, the correct identification of local environment and microenvironment is very important. Some decisive micro-environments such as the underside of the bridge (especially on the water), the roof of an indoor swimming pool, the sun and shade of the building.

Corrosion in water and soil
Pay special attention when a part of the steel structure is immersed in water or buried in the soil. In this case, the corrosion is usually concentrated in a small part of the location where the corrosion rate is high. It is not recommended to use exposure tests to assess the corrosivity of water and soil environments. However, different flooding and burial situations can be described.

Structure submerged in water
The types of water include fresh water, salt water or sea water, which have a serious impact on the corrosion of steel. Corrosion is also affected by the oxygen content in the water, the type and amount of dissolved substances, and the water temperature. The growth of animals and vegetables will also accelerate corrosion. The water immersion environment can be divided into the following three types of areas:
Underwater area: a place permanently submerged in water;
Intermediate area (fluctuating water level): The area where the water level fluctuates due to natural or man-made factors and is aggravated by the intermittent cooperation of water and atmosphere;
Wave splash area: The area splashed by waves and water mist can cause abnormally high corrosion stress, especially salt water.

Structure buried in soil
The corrosiveness of soil is related to the mineral content and physical properties, organic content, water content and oxygen content in the soil. The corrosiveness of the soil is greatly affected by aeration. Changes in oxygen content can cause corrosion to form a galvanic effect. In most steel structures such as pipelines, tunnels, storage tanks, etc., in different types of soils, soils with different oxygen content, soils with different groundwater levels, etc., local corrosion (pitting corrosion) is enhanced due to the corrosion battery effect. ) Began to worsen.

Special case
When choosing a coating protection system, the special corrosion stress of the steel structure and the special position of the steel structure must be considered, such as corrosion by acid, alkali, salt and other corrosive media.