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The Chemistry of Oxygen Corrosion in Wet Pipe Fire Sprinkler Systems and WPNI for Corrosion Control

The Chemistry of Oxygen Corrosion in Wet Pipe Fire Sprinkler Systems and WPNI for Corrosion Control (195 kb)

There is a lot of misinformation circulating within the fire sprinkler industry regarding oxygen corrosion of steel sprinkler piping and the mechanisms associated with that process. Oxygen is a highly reactive gas constituent of the air we breathe (21%) and is the primary cause of corrosion in fire sprinkler piping. There are three physical attributes of oxygen gas that greatly affect the corrosion reaction with steel pipe.

    1. Oxygen gas exhibits very low solubility in water.
    2. Once the dissolved oxygen in water contacts the steel pipe, the reaction between the oxygen and the iron occurs in minutes.
    3. Oxygen molecules that are dissolved in water have very poor mobility in stagnant water.

These three physical attributes clearly explain why almost all of the corrosion that occurs in wet pipe fire sprinkler systems occurs in close proximity to pockets of trapped air within the water filled piping.

Some in the industry who are unfamiliar with oxygen corrosion chemistry have suggested that it is necessary to remove the dissolved oxygen from fire sprinkler supply water before it is used to fill the sprinkler system piping. However, a simple analysis of the total amount of oxygen in the piping reveals there is at least 5,000 times more oxygen available for corrosion in the trapped gas of a wet pipe fire sprinkler system than there is in the fill water. Focusing on the very small amount of oxygen contained in the incoming water supply is costly, inefficient, and unproductive.