Corrosion in condensate lines is mainly caused by:

Corrosion in condensate lines is primarily attributed to the presence of oxygen and carbon dioxide. When steam condenses in the piping, it can dissolve these gases, leading to the formation of carbonic acid in the presence of water. This acid is highly corrosive and can cause significant damage to the metal components of condensate lines over time.

Oxygen is another significant contributor; it can lead to pitting and general corrosion of the metal when it is present in the condensate. The combination of these two gases creates a highly corrosive environment, ultimately compromising the integrity of the piping.

Other factors like nitrogen do not contribute significantly to corrosion as it is inert under these conditions and does not form harmful compounds with water. Similarly, while amine can be involved in steam treatment processes, it does not inherently cause corrosion in the same way that oxygen and carbon dioxide do. Condensed steam itself is not a corrosive agent but is rather a product of the condensation process that can carry potential contaminants but does not directly cause corrosion. Thus, the combination of oxygen and carbon dioxide stands out as the primary cause of corrosion in condensate lines.