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White Paper: Chemistry of Corrosion in Wet Pipe Sprinkler Systems

Note: this information appeared in a white paper featured in a previous issue of FPC Magazine.

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 and the primary cause of corrosion in fire sprinkler piping. Oxygen gas has three physical attributes that greatly affect its corrosion reaction with steel pipe:

Source of Oxygen in Wet Pipe Fire Sprinkler Systems

Source of Oxygen in Wet Pipe Fire Sprinkler Systems

  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 takes place in close proximity to pockets of trapped air and not at other locations that are completely water filled.

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 the water 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.