1) Atmospheric relative humidity

The ratio of the amount of water vapor in the atmosphere to the amount of water vapor saturated at the same temperature is called relative humidity. Below a certain relative humidity, the corrosion rate of metal is very small, but above this relative humidity, the corrosion rate increases sharply. This relative humidity is called the critical humidity. The critical humidity for many metals is between 50% and 80%, and for steel it is about 75%. Atmospheric relative humidity has the greatest influence on metal corrosion. When the atmospheric humidity is higher than the critical humidity, the metal surface will appear water film or water droplets, if the harmful impurities contained in the atmosphere dissolve soil water film, water droplets, that is, into the electrolyte, aggravating corrosion.

2) Temperature and humidity

The correlation between atmospheric temperature and humidity affects metal corrosion. Here are the main things: first, the amount of water vapor in the atmosphere increases with temperature; Second, high temperature aggravates corrosion, especially in humid environment. The higher the temperature, the faster the corrosion speed. When the relative humidity is low, the influence of temperature on corrosion is not obvious, but when the relative humidity is higher than the critical humidity, the corrosion amount increases sharply with the increase of temperature. In addition, if there is a temperature difference between the atmosphere and the metal, condensation water will form on the metal surface at a low temperature, which will also lead to metal rust.

3) Corrosive gases

The corrosive gas in the air is sulphur dioxide, which has the greatest influence on the corrosion of metals, especially on steel, copper and its alloys. The sulfur dioxide in the atmosphere mainly comes from the burning of coal. At the same time, the combustion product carbon dioxide also has a corrosive effect. The atmosphere around the plant is mixed with corrosive gases. Such as hydrogen sulfide, ammonia, hydrochloric acid gas, etc. are the factors that promote metal corrosion.