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Inspectioneering Journal

99 Diseases of Pressure Equipment: Boiler Feed Water Corrosion

By John Reynolds at Intertek. This article appears in the May/June 2005 issue of Inspectioneering Journal

Boiler feed water (BFW) corrosion is mostly the result of dissolved oxygen in the feedwater, but is also related to the quality of the BFW and the quality of the treatment system. If the treatment system is effective, then a layer of iron oxide (magnetite) will provide the protection needed to minimize boiler corrosion. If the treatment is not effective or the quality varies from time-to-time then pitting type corrosion can occur in the entire front end of the boiler, including the treating system, deaerator, feedwater lines/ pumps, and preheat coils. Higher pressure and temperature boiler systems tend to be more difficult to control to the specifications required for minimizing BFW corrosion. Chemical treatment for scale and deposit control must be tuned to coordinate with the oxygen scavenger (typically sodium sulfite or hydrazine) and tuned for the specific water quality and BFW treating system. Routine water analysis is the best monitoring tool to make sure that treatment systems are functioning properly. There is no economical or effective pro-active inspection method for BFW corrosion. Ineffective BFW treatment usually reveals itself with leaks or tube ruptures in the water sections of the boiler. Be careful not to let your BFW treatment program become “out-of-sight - out-of-mind”, as it will surely “bite you” if it does. The other related problem that occurs in BFW systems (especially deaerators) is corrosion fatigue (covered separately).

Do you know if your BFW treatment is economical and effective 100% of the time? If not, you may pay the price in reduced boiler reliability.


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