Unlike the corrosion of duplex steel pipes immersed in a liquid solution, atmospheric corrosion refers to the corrosion of duplex stainless steel pipes exposed to the air.

Atmospheric corrosion summarizes a wide range of conditions, so the classification of atmospheric corrosion is diverse. Some are classified according to geography and the air containing trace elements (industrial, marine and rural); some are classified by climate (tropical, humid tropical, temperate, etc.); and some are classified according to the attachment state of water vapor on the metal surface.

From the perspective of corrosion conditions, the main components of the atmosphere are water and oxygen, and the water vapor in the atmosphere is the main factor that determines the corrosion rate and history of the atmospheric duplex stainless steel pipe. Therefore, atmospheric corrosion can be divided into three types: “dry”, “moist” and “wet” according to the degree of humidity of the corroded metal surface.

Dry atmospheric corrosion is also called dry oxidation and low humidity corrosion, that is, atmospheric corrosion when there is basically no water film on the surface of the duplex steel pipe. This kind of corrosion belongs to room temperature oxidation in chemical corrosion. In a clean and dry room temperature atmosphere, most metals form an extremely thin invisible oxide film with a thickness of 10-40A.

When the relative humidity is below 100%, metal corrosion occurs under a thin water film that is invisible to the naked eye. Such as iron rusting when it is not exposed to rain or snow. This layer of water film is formed on the metal surface due to the action of dual-phase steel pipe, adsorption or chemical aggregation. Therefore, the concentration of this corrosive water vapor must exceed a certain minimum value (critical humidity). In addition, it also requires the presence of a small amount of gas contamination or solid contamination. When the critical humidity is exceeded, the presence of contamination greatly increases the corrosion rate of the surface of the duplex steel pipe.

Posted by stainless steel pipe and fittings supplier, KAYSUNS.