Corrosive Gases in Steam and Condensate Systems

Oxygen, nitrogen, carbon dioxide, ammonia, hydrogen sulfide, sulfur dioxide, and other contaminant gases are generally present to some degree in all steam and condensate systems. 

Depending on the degree of oxygen infiltration, the temperature of the condensate and the presence of other gases such as carbon dioxide, various corrosion reactions may take place in the steam distribution and CR systems. The most basic reaction associated with oxygen infiltration results in oxygen corrosion, which can produce deep pitting in the pipework and is described later in this chapter. 

Oxygen infiltration coupled with (steam volatile) carbon dioxide produces enhanced condensate line corrosion. The corrosion rate of steel in the system is particularly high when both gases are present. 

Copper and brasses in the systems are more resistant to corrosion because of a stable oxide film however, if ammonia is present together with oxygen, corrosion of copper and copper oxide rapidly occurs. The corrosion is an oxidation process and results in the formation of the ammonia-copper complex [Cu(NH3)42+], Corrosion of nickel and zinc components also may occur in like fashion. 

oxygen infiltration gives rise to a range of localized steam and condensate system corrosion reactions and products. These reactions may, in turn, lead to further downstream problems of corrosion debris transport when the condensate returns to the FW system. 

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