Corrosion in boilers generally occurs when the alkalinity of boiler water is low, or when the metal is exposed to oxygen during service or idle times.
In the case of high temperatures and high stresses in the boiler, the metal tends to accelerate the corrosion mechanisms. In steam and condensing systems, corrosion is generally the result of carbon dioxide or oxygen contamination.
Specific contaminants such as ammonia or sulfide carried by gases can increase the attack on copper in the system.

Corrosion is caused by the combination of an oxide layer and continuous oxidation carried by oxygen. The protection of steel in a boiler system depends on temperature, Ph, and oxygen content. Generally speaking, higher temperatures, high or low pH levels and high oxygen concentrations increase the corrosion rate of steel.