What Does Dew Point Corrosion Mean?
Dew point corrosion is corrosion damage that occurs when the air reaches a temperature at which the evaporating and condensing rate of its moisture content are the same at a constant pressure. This is experienced when the air is humid, foggy, moist, sticky and misty.
Since moisture is produced at the dew point, knowledge of this weather element helps in the selection of metals. Moisture is an important factor in corrosion types such as rusting. Additionally, the moisture can react with airborne gases like sulfur and chloride, which form acids that attack metallic surfaces, particularly in oil refineries.
Corrosionpedia Explains Dew Point Corrosion
Acid dew point corrosion is very common in the oil industry. The acidity is formed by flue gases which are produced in the refinery. The flue gases combine with the moisture content in the air and form a specific dew point. When the temperature reaches the dew point, the acid becomes liquid and attacks the surface of metallic materials.
Dew point corrosion is largely an internal corrosion that occurs in storage equipment and structures. If the gases escape to the atmosphere, the external surfaces of pipes might corrode. Common flue gases include:
- Sulfuric oxides
- Carbon monoxide
- Nitrogen oxides
Preventing dew point corrosion by moderating temperatures and pressures reduces the rate at which pipes must be replaced.